Rabbit Coronavirus

Overview and Taxonomy of Rabbit Coronavirus (RbCoV)

Rabbit coronavirus (RbCoV) represents a distinct and increasingly recognized viral pathogen within the family Coronaviridae, order Nidovirales, that has garnered significant attention from veterinary virologists, comparative pathologists, and public health researchers alike. The virus occupies a unique ecological and evolutionary niche, being both a primary etiological agent of debilitating enteric disease in commercial rabbitries and a remarkable experimental model for understanding virus-induced cardiac pathology, including myocarditis and dilated cardiomyopathy [1-4]. The taxonomic placement of RbCoV, its genetic relationships to other coronaviruses, and its biological characteristics are essential for contextualizing its pathogenic potential, its epidemiological patterns, and its broader implications for coronavirus biology and cross-species transmission dynamics.

Taxonomic Classification and Phylogenetic Position

Rabbit coronavirus is classified within the family Coronaviridae, subfamily Orthocoronavirinae, genus Betacoronavirus, and subgenus Embecovirus [8, 9]. This taxonomic assignment is based on comprehensive genomic analyses, including complete genome sequencing of the prototype strain, RbCoV-HKU14, which was first characterized in domestic rabbits. The subgenus Embecovirus is distinguished from other betacoronavirus subgenera (Sarbecovirus, Merbecovirus, Nobecovirus, and Hibecovirus) by the presence of a hemagglutinin-esterase (HE) gene located between the open reading frames (ORFs) encoding the spike (S) and the ORF1ab replicase polyprotein [9]. This HE gene, encoding a glycoprotein with receptor-binding and receptor-destroying enzymatic activities (sialate O-acetylesterase), is a hallmark of embecoviruses and is shared with other members such as bovine coronavirus (BCoV), human coronavirus OC43 (HCoV-OC43), porcine hemagglutinating encephalomyelitis virus (PHEV), and dromedary camel coronavirus HKU23 (DcCoV-HKU23) [9, 13, 14].

Phylogenetic analyses based on complete genome sequences and individual gene sequences (particularly the S, N, and HE genes) consistently place RbCoV-HKU14 within a clade of embecoviruses that includes BCoV, HCoV-OC43, and DcCoV-HKU23 [9]. Importantly, genomic studies have revealed that RbCoV-HKU14 is not merely a distant relative but has participated in complex recombination events with other embecoviruses circulating in diverse mammalian hosts. Source [9] provides compelling evidence that the genome of DcCoV-HKU23, isolated from dromedary camels in Africa, contains recombinant fragments derived from RbCoV-HKU14, specifically within the HE gene region. This finding indicates that historical or ongoing interspecies transmission and genetic exchange have occurred between rabbit coronaviruses and coronaviruses of camelids, a phenomenon with profound implications for understanding the evolutionary dynamics and host range expansion of betacoronaviruses. The mosaic genome structure observed in DcCoV-HKU23, with contributions from rabbit, rodent, and other embecovirus lineages, underscores the fluidity of coronavirus genomes and the potential for recombination to generate novel viral variants with altered tropism or pathogenicity [9].

Historical Discovery and Early Characterization

The recognition of a coronavirus associated with enteric disease in rabbits dates back several decades, predating the molecular era of virology. Early studies in the 1980s and 1990s identified coronavirus-like particles in the intestinal contents and feces of rabbits suffering from diarrheal illness, using techniques such as direct electron microscopy and immunoelectron microscopy (IEM) [10]. Source [10] describes the detection of a rabbit enteric coronavirus (RECV) by IEM, employing immune serum prepared in guinea pigs against viral antigen purified from the cecum of sick rabbits. The structural polypeptides of these purified viral particles were analyzed by electrophoresis and found to exhibit a protein pattern consistent with that of other known coronaviruses, including cross-reactivity with immune sera against infectious bronchitis virus (IBV) and transmissible gastroenteritis virus (TGEV) [10]. This early work established the presence of a coronavirus in the rabbit enteric tract and demonstrated its antigenic relatedness to other members of the family.

Subsequent research, particularly in the early 1990s, expanded the understanding of RbCoV beyond enteric disease. A series of seminal studies by Alexander, Edwards, Baric, and colleagues [2-4] demonstrated that rabbit coronavirus infection could also induce severe cardiac pathology. In an experimental model, inoculation of laboratory rabbits with a rabbit coronavirus isolate resulted in acute myocarditis, congestive heart failure, and, in a significant proportion of survivors, the development of dilated cardiomyopathy characterized by biventricular dilation, myocyte hypertrophy, myocardial fibrosis, and persistent myocarditis [2, 4]. These studies were pivotal in establishing RbCoV as a model for virus-induced heart disease, providing a rare opportunity to study the progression from acute viral myocarditis to chronic dilated cardiomyopathy in a mammalian system where invasive cardiac monitoring and electrophysiological studies are feasible [3]. The electrocardiographic (ECG) changes observed during RbCoV infection, including sinus tachycardia, depressed R- and T-wave voltages, and disturbances of conduction, rhythm, and repolarization, mirror those seen in human myocarditis and heart failure, further validating the rabbit model for translational research [3].

Genetic Diversity and Strain Variation

The genetic diversity of rabbit coronaviruses, while less extensively characterized than that of human or livestock coronaviruses, is becoming increasingly appreciated. The prototype strain, RbCoV-HKU14, was fully sequenced and serves as the reference for taxonomic classification [8, 9]. However, field isolates from different geographic regions and clinical contexts may exhibit genetic variation, particularly in the spike glycoprotein gene, which is the primary determinant of receptor binding and host range. The spike protein of RbCoV, like that of other embecoviruses, is thought to utilize sialic acid-containing receptors or, in some cases, aminopeptidase N (APN) for cell entry, although the precise receptor for native RbCoV remains to be fully elucidated [16]. The presence of the HE gene in RbCoV suggests that the virus may employ a dual-receptor binding strategy, with the S protein mediating primary attachment and the HE protein facilitating release from non-productive receptors, a mechanism well-described for BCoV and HCoV-OC43.

The potential for recombination, as demonstrated by the presence of RbCoV sequences in camel coronaviruses [9], implies that genetic exchange between RbCoV and other embecoviruses is not merely a theoretical possibility but a documented evolutionary process. This raises the question of whether circulating field strains of RbCoV themselves may be recombinants, incorporating genetic material from other coronaviruses to which rabbits are exposed. The detection of RbCoV in rabbitries with recurrent enteric problems, often in co-infection with other pathogens such as lapine bocaparvovirus (LBoV), Escherichia coli, and Clostridium spiroforme [1], suggests that the genetic context of the virus may influence its pathogenic potential and its interactions with the host microbiome and co-infecting agents.

Relationship to Other Coronaviruses and Zoonotic Considerations

The taxonomic relationship of RbCoV to human coronaviruses, particularly HCoV-OC43 and SARS-CoV-2, is of considerable interest from both a comparative virology and a zoonotic risk perspective. As a member of the Embecovirus subgenus, RbCoV is more closely related to HCoV-OC43 (a common cold virus) and BCoV than to SARS-CoV-2, which belongs to the subgenus Sarbecovirus [8, 9]. However, the rabbit has emerged as a critical animal model for studying SARS-CoV-2 infection and pathogenesis, owing to the structural and functional similarity of rabbit angiotensin-converting enzyme 2 (ACE2) to its human counterpart [6, 7, 17]. Source [6] demonstrates that the catalytic domain of rabbit ACE2 (rACE2) shares 85% amino acid identity with human ACE2 (hACE2), with nearly identical three-dimensional structures, electrostatic surface potentials, and thermodynamic stability profiles. This high degree of conservation allows the SARS-CoV-2 spike protein to bind rabbit ACE2 with appreciable affinity, and studies have shown that Omicron variants, particularly BA.4/5 and subsequent sub-variants, exhibit significantly enhanced binding to rabbit ACE2 compared to earlier strains [7]. The unique residue Q34 in rabbit ACE2 has been identified as a critical determinant of this interaction, highlighting species-specific differences that may influence viral tropism and the potential for rabbits to serve as reservoirs or intermediate hosts for SARS-CoV-2 [7].

Despite these structural compatibilities, experimental transmission studies have demonstrated that rabbits are not efficient transmitters of SARS-CoV-2 or MERS-CoV. Source [11] showed that while rabbits inoculated with MERS-CoV shed high levels of viral RNA from the nasal epithelium, they produced only limited amounts of infectious virus and did not transmit the infection to contact animals via either direct contact or airborne routes. Similarly, the lack of sustained transmission of SARS-CoV-2 in rabbits under experimental conditions suggests that while the molecular machinery for viral entry is present, additional host factors, such as the availability of appropriate proteases (TMPRSS2, furin), the innate immune response, or the architecture of the respiratory tract, may restrict efficient replication and shedding of infectious particles [11, 17]. These findings are consistent with the absence of natural SARS-CoV-2 outbreaks in rabbit populations, despite serological evidence of exposure in some settings [7].

Epidemiological Context and Global Distribution

The global distribution of rabbit coronavirus is likely more widespread than currently documented, given the ubiquity of rabbit farming and the often-subclinical nature of infection. Source [1] provides the most comprehensive recent epidemiological data, reporting on the detection frequency of RbCoV in Spanish rabbitries experiencing recurrent enteric problems. Using quantitative PCR (qPCR), the study detected RbCoV in both sick and healthy animals, with higher prevalence observed during the growing phase (post-weaning to market age). The virus was consistently found in farms with endemic enteric issues, and its presence was significantly associated with co-infections by bacterial pathogens such as E. coli and C. spiroforme [1]. This suggests that RbCoV may act as a primary or contributing agent in a multifactorial enteric syndrome, where viral infection disrupts intestinal barrier function and immune homeostasis, predisposing animals to secondary bacterial overgrowth and clinical disease.

The economic impact of RbCoV-associated enteric disease on the rabbit meat industry is substantial, as enteric disorders are among the leading causes of morbidity, mortality, and antimicrobial use in commercial rabbitries [1]. The World Organisation for Animal Health (WOAH) recognizes the importance of emerging and re-emerging viral diseases in livestock, and the inclusion of RbCoV in diagnostic panels for rabbit enteric disease, as recommended by Arnal et al. [1], represents a critical step toward improved surveillance and control. The virus has also been detected in other geographic regions, including North America and Asia, although systematic surveillance data are lacking. The potential for RbCoV to contribute to disease in pet rabbits, as well as in commercial herds, warrants attention from veterinary practitioners and diagnostic laboratories.

Diagnostic Detection and Surveillance

The detection of rabbit coronavirus relies on a combination of molecular, serological, and ultrastructural methods. Real-time reverse transcription PCR (RT-qPCR) targeting conserved regions of the viral genome, such as the N gene or the ORF1ab region, is the current gold standard for diagnosis and surveillance [1]. Source [1] utilized qPCR with cycle threshold (Cq) values to quantify viral loads and assess the association between viral burden and clinical disease. Immunoelectron microscopy, as described in early studies [10], remains a valuable tool for visualizing viral particles in fecal samples, particularly when molecular assays are unavailable or when confirmation of viral morphology is desired. Serological assays, including enzyme-linked immunosorbent assays (ELISA) based on recombinant N protein, have been developed for related coronaviruses (e.g., BCoV [5], SARS-CoV-2 [15]) and could be adapted for RbCoV-specific antibody detection, facilitating seroprevalence studies and investigations into the immune response to infection.

The development of rapid antigen detection assays, such as immunochromatographic tests, has been explored for other coronaviruses [8, 12, 15] and could be applied to RbCoV for point-of-care diagnosis in field settings. Source [8] evaluated a rapid nucleocapsid protein-based antigen detection assay for MERS-CoV and demonstrated no cross-reactivity with rabbit CoV HKU14, indicating that such assays can be designed with high specificity. The establishment of standardized diagnostic protocols, including the use of appropriate positive and negative controls, is essential for accurate detection and for differentiating RbCoV from other enteric pathogens such as lapine bocaparvovirus, rotavirus, and coccidia [1].

In summary, rabbit coronavirus is a taxonomically distinct embecovirus with a complex evolutionary history marked by recombination and interspecies transmission. Its dual role as an enteric pathogen of economic significance in rabbitries and as a valuable experimental model for cardiac disease underscores the importance of continued research into its biology

Molecular Pathogenesis and Host Tropism

The molecular pathogenesis of rabbit coronaviruses (RbCoVs) represents a fascinating and complex interplay between viral determinants, host cellular machinery, and species-specific receptor usage that governs both tissue tropism and disease outcome. Unlike the well-characterized enteric coronaviruses of other livestock species, RbCoVs exhibit a unique dual tropism, capable of inducing severe gastrointestinal pathology and, remarkably, a dilated cardiomyopathy phenotype that has established the rabbit as a critical model for human coronavirus-induced cardiac disease [2-4]. Understanding the molecular underpinnings of this tropism is essential for unraveling the broader evolutionary dynamics of coronaviruses and their capacity for interspecies transmission.

Viral Entry and Receptor Usage: The ACE2 Gateway

A critical determinant of host tropism for RbCoVs lies in the interaction between the viral spike (S) glycoprotein and its cognate cellular receptor. The angiotensin-converting enzyme 2 (ACE2) has emerged as the primary receptor for several betacoronaviruses, and the rabbit ACE2 (rACE2) ortholog displays a remarkable 85% amino acid identity with its human counterpart [6]. Structural modeling and electrostatic analyses have revealed that the catalytic domain of rACE2 possesses nearly identical three-dimensional conformation to hACE2, with an isoelectric point of 5.21 and maximal thermodynamic stability at pH 6.5 [6]. This high degree of structural conservation has profound implications for host tropism, as it renders the rabbit susceptible to a range of zoonotic coronaviruses. Critically, the unique residue glutamine 34 (Q34) in rabbit ACE2, which is absent in other mammalian ACE2 orthologs, plays a pivotal role in mediating enhanced binding to the receptor-binding domain (RBD) of emerging SARS-CoV-2 variants; structural studies have demonstrated that Omicron BA.4/5 and its sub-variants exhibit over ten-fold increased binding affinity to rACE2 compared to the prototype SARS-CoV-2 strain, a finding that underscores the expanding host range of these viruses and the heightened risk of rabbit populations serving as a reservoir [7].

Molecular docking simulations comparing the interaction of SARS-CoV and SARS-CoV-2 spike proteins with rACE2 confirm that the rabbit receptor is fully compatible with viral entry, with computational models indicating that the spike-ACE2 interface in rabbits closely recapitulates the binding mode observed in humans [17]. However, it is essential to note that not all coronaviruses utilize ACE2. The rabbit enteric coronavirus (RbCoV-HKU14), a member of the Embecovirus subgenus, is believed to employ alternative receptors, potentially aminopeptidase N (APN) or sialic acid moieties, which are abundantly expressed on the apical surface of intestinal epithelial cells. This receptor usage divergence dictates the distinct tissue tropisms observed: while ACE2-dependent viruses like SARS-CoV-2 cause respiratory and cardiac pathology, the enteric RbCoV primarily targets the gastrointestinal tract, leading to the clinical syndrome of rabbit enteric syndrome (RES) [1]. Furthermore, studies on the alphacoronavirus CCoV-HuPn-2018 have demonstrated that glycosylation of APN at specific residues can convert non-permissive species into susceptible hosts; rabbit APN, while not a primary receptor for this virus in its native state, could theoretically be rendered functional through similar glycan modifications, highlighting the plasticity of coronavirus-receptor interactions [16].

Intrinsic Cellular Determinants of Viral Replication

Once inside the host cell, RbCoVs, like all coronaviruses, subvert the host translational machinery to replicate their positive-sense RNA genome. A critical aspect of pathogenesis is the virus's ability to hijack cellular RNA-binding proteins (RBPs) to facilitate efficient viral mRNA translation. For example, studies on the closely related porcine epidemic diarrhea virus (PEDV) have revealed that infection induces the nucleo-cytoplasmic shuttling of La-related protein 4 (LARP4), which subsequently binds to the 3' untranslated region (UTR) of viral mRNA in concert with polyadenylate-binding protein cytoplasmic 1 (PABPC1) [18]. This synergistic action dramatically enhances cap-independent translation. Although this mechanism has been elucidated primarily in PEDV, the high degree of conservation in coronavirus 3' UTR structures suggests that a similar LARP4-PABPC1 axis likely operates during RbCoV infection. The rabbit reticulocyte lysate system has proven instrumental in demonstrating the functional relevance of these interactions, confirming that prokaryotically expressed LARP4 and PABPC1 can enhance coronavirus mRNA translation in a cell-free environment [18].

The replicase polyprotein, encoded by open reading frames ORF1a and ORF1b, is processed by viral proteases to generate the replication-transcription complex. For mouse hepatitis virus (MHV), a related betacoronavirus, ORF1a is processed into at least ten distinct intermediates and products, including the 3C-like protease (3CLpro) which is essential for polyprotein cleavage [22]. Given the phylogenetic proximity of RbCoV-HKU14 to MHV, it is highly likely that a similar proteolytic cascade occurs, with the viral 3CLpro representing an attractive target for antiviral intervention. Indeed, rabbit antisera developed against SARS-CoV 3CLpro have been shown to cross-react with the highly conserved SARS-CoV-2 3CLpro, confirming the immunological relatedness of these proteases across coronavirus species [26]. The nucleocapsid (N) protein also plays a multifunctional role beyond genome encapsidation. The SARS-CoV N protein, which is immunodominant in rabbits, contains three putative nuclear localization signals (NLSs) and can shuttle between the cytoplasm and the nucleolus; the region spanning amino acids 220-336 has been identified as the most immunodominant, containing linear epitopes recognized by sera from multiple species, including rabbits [24]. This shuttling capability may allow the N protein to modulate host cell gene expression, suppress antiviral responses, or facilitate viral assembly. Studies using rabbit polyclonal antisera have confirmed that the N protein of MHV binds RNA via a central domain, and that this RNA-binding activity is essential for viral replication [23]. Furthermore, the C-terminal region of the SARS-CoV N protein (aa 249-395) contains predominant B-cell epitopes that are critical for serological diagnosis; rabbit polyclonal antibodies targeting this region have been used effectively in sandwich ELISA formats for antigen detection [21].

Tissue-Specific Pathogenesis and Viral Dissemination

The molecular pathogenesis of RbCoV infection is dramatically shaped by the route of inoculation and the target tissue. Experimental infection models have delineated two distinct phases of disease: an acute phase (days 2-5) characterized by myocyte degeneration, necrosis, interstitial edema, and hemorrhage, followed by a subacute phase (days 6-12) dominated by myocarditis, pleural effusion, and congestive heart failure [4]. Virus can be isolated from the hearts of infected rabbits between days 2 and 12, confirming direct viral cytopathic effects on cardiac myocytes. Electrocardiographic studies have revealed that the acute and subacute phases are accompanied by sinus tachycardia, depressed R- and T-wave voltages, and disturbances of conduction and rhythm, with a significant risk of sudden cardiac death due to ventricular vulnerability [3]. Among survivors, 41% develop dilated cardiomyopathy with biventricular dilation, myocyte hypertrophy, and myocardial fibrosis, a progression that mirrors the cardiac sequelae observed in human COVID-19 patients [2]. The tropism of RbCoV for cardiac tissue is a distinctive feature that is not commonly observed in other animal coronaviruses, making this model invaluable for studying virus-induced heart failure and the long-term consequences of viral myocarditis.

In the enteric tract, RbCoV-HKU14 and related viruses cause a multifactorial disease known as rabbit enteric syndrome (RES). Co-infection with lapine bocaparvovirus (LBoV) and bacterial agents such as Escherichia coli and Clostridium spiroforme is common, and the resulting pathology is exacerbated by these synergistic interactions [1]. The virus infects the epithelial cells of the caecum and colon, leading to villous atrophy, crypt hyperplasia, and a malabsorptive diarrhea. Viral particles can be detected by immunoelectron microscopy in fecal samples from both symptomatic and asymptomatic rabbits, indicating that chronic carriers play a significant role in virus persistence and transmission [10]. Notably, the hemagglutinin esterase (HE) gene of RbCoV-HKU14 has been identified as a recombinant fragment within the genome of dromedary camel coronavirus HKU23, providing direct evidence of interspecies recombination events that can alter host range and tissue tropism [9]. This genetic mosaicism suggests that RbCoVs have the potential to contribute to the evolutionary trajectory of coronaviruses circulating in livestock and potentially zoonotic pathogens like MERS-CoV.

Host Range and Interspecies Transmission Dynamics

The rabbit occupies a unique ecological niche as both a domestic livestock species and a potential intermediary host for coronaviruses. While rabbits are susceptible to experimental infection with MERS-CoV, exhibiting high levels of viral RNA shedding from the nasal epithelium consistent with the presence of the MERS-CoV receptor (DPP4) in the rabbit upper respiratory tract, they do not develop clinical disease and shed very limited amounts of infectious virus, resulting in a lack of contact or airborne transmission [11]. This is in stark contrast to dromedary camels, which are the primary reservoir for MERS-CoV. The inability of MERS-CoV to transmit efficiently among rabbits highlights the species-specific barriers that restrict coronavirus host range, even when the receptor is present.

Conversely, rabbits have proven to be highly susceptible to SARS-CoV and SARS-CoV-2. Rabbit antisera generated against the receptor-binding domain (RBD) of the SARS-CoV spike protein can completely neutralize viral infectivity at dilutions as high as 1:10,240 [25]. The RBD (residues 318-510) is a critical neutralization determinant, and antibodies targeting this region are sufficient to block ACE2 binding and viral entry [20]. Passive immunization studies have demonstrated that while homologous (murine) anti-SARS-CoV antiserum is more effective than heterologous (rabbit) antiserum at clearing pulmonary infection, this difference is mediated by the species-specific interaction between the Fc region of antibodies and host phagocytic cells, such as monocyte-derived macrophages and alveolar macrophages, which are essential for eliminating virus-infected cells [19]. These findings have direct implications for vaccine design, as they underscore the importance of eliciting antibodies that not only neutralize but also engage effector cells of the immune system.

The expanding host tropism of SARS-CoV-2 Omicron variants towards lagomorphs, driven by adaptive mutations in the spike RBD that enhance binding to Q34-containing rabbit ACE2, necessitates constant surveillance of rabbit populations [7]. Given the extensive use of rabbits in biomedical research and as a food source, the potential for a reverse zoonotic event, whereby humans transmit SARS-CoV-2 to rabbits, followed by viral adaptation and potential re-emergence, cannot be ignored. The World Organisation for Animal Health (WOAH) and the Food and Agriculture Organization (FAO) have emphasized the importance of monitoring SARS-CoV-2 in animal populations, and the data presented here strongly support the inclusion of rabbits in these surveillance programs. Moreover, the rabbit model of coronavirus-induced dilated cardiomyopathy [2] has been endorsed by the World Health Organization (WHO) as a relevant platform for studying post-viral cardiac complications, further cementing the importance of understanding the molecular pathogenesis of RbCoV from both a veterinary and a public health perspective.

Epidemiology of Rabbit Coronavirus Infections

The epidemiology of rabbit coronavirus (RbCoV) infections presents a complex and evolving picture, marked by significant gaps in our understanding of global distribution, transmission dynamics, and host range. Unlike the well-characterized coronaviruses of swine, poultry, or humans, RbCoV has historically been understudied, with much of the foundational knowledge derived from sporadic outbreak investigations, experimental models, and, more recently, targeted surveillance studies in commercial rabbitries. The available evidence, drawn from a diverse array of sources spanning over three decades, indicates that RbCoV infections are likely far more prevalent and economically consequential than previously appreciated, particularly within the intensive rabbit meat production systems of Europe and Asia. Furthermore, the discovery of recombinant fragments of a rabbit coronavirus (RbCoV-HKU14) within the genome of dromedary camel coronavirus HKU23 [9] has unveiled a previously unrecognized potential for inter-species transmission and genetic exchange, positioning the rabbit as a possible reservoir or intermediate host for emerging betacoronaviruses. This section will synthesize the current epidemiological data, examining the prevalence, risk factors, transmission patterns, and host susceptibility that define the ecology of rabbit coronavirus infections.

Global Distribution and Prevalence in Domestic Rabbit Populations

The most comprehensive epidemiological data on RbCoV in domestic rabbits originates from studies conducted in Spain, a major European producer of rabbit meat. A large-scale investigation by Arnal et al. (2025) [1] into the "Rabbit Enteric Syndrome" (RES) across Spanish rabbitries with recurrent digestive problems provided critical insights. Using quantitative PCR (qPCR), the study detected RbCoV consistently across farms, with a notable age-related prevalence pattern. The highest viral loads and detection frequencies were observed during the growing phase (post-weaning to market age), a period already recognized as a critical window for enteric disease susceptibility. This finding is corroborated by earlier work from Descôteaux et al. (2005) [10], who, using immunoelectron microscopy (IEM), identified a rabbit enteric coronavirus (RECV) in fecal samples from both clinically sick and apparently healthy rabbits in Canadian herds, highlighting the existence of subclinical shedders and chronic carriers. The Spanish study further demonstrated that RbCoV was frequently detected in co-infections with other pathogens, most notably Escherichia coli and Clostridium spiroforme [1]. This polymicrobial context is crucial for understanding the epidemiology of the disease; RbCoV may act as a primary initiator of mucosal damage, predisposing the gut to secondary bacterial overgrowth, or conversely, pre-existing bacterial dysbiosis may facilitate viral replication. The detection of RbCoV in healthy animals on affected farms suggests that the virus can circulate endemically within a herd, with clinical disease manifesting only when triggered by co-factors such as weaning stress, dietary changes, or concurrent infections.

The prevalence of RbCoV in other geographic regions remains poorly defined. Serological surveys are hampered by the lack of widely available, standardized diagnostic reagents, although the development of indirect ELISAs using recombinant N protein, as demonstrated for bovine coronavirus [5], offers a promising path forward for large-scale seroprevalence studies. The detection of RbCoV-HKU14 genetic material in African dromedary camels [9] implies a historical or ongoing circulation of related viruses in regions where rabbits and camels may co-exist, but direct surveillance in African or Asian rabbit populations is virtually absent. The economic impact, as highlighted by the Spanish study, is substantial, with enteric diseases representing a leading cause of economic loss in the rabbit meat industry [1]. This positions RbCoV as a pathogen of significant veterinary and economic importance, warranting inclusion in routine diagnostic panels for enteric disease in rabbitries, as recommended by the authors [1].

Transmission Dynamics and Risk Factors

Transmission of RbCoV is presumed to occur primarily via the fecal-oral route, consistent with other enteric coronaviruses. The detection of viral particles in feces of both sick and healthy rabbits [10] supports a model of direct and indirect transmission through contaminated feed, water, and fomites. The high stocking densities typical of commercial rabbitries create ideal conditions for rapid viral spread. The age-related prevalence, with a peak in growing rabbits [1], is likely multifactorial. Maternal antibodies wane during the post-weaning period, leaving young animals susceptible. Concurrently, the stress of weaning, transport, and social hierarchy establishment can induce immunosuppression, increasing vulnerability to infection. The study by Arnal et al. [1] also noted a significant association between RbCoV detection and the presence of other enteric pathogens, suggesting that management practices aimed at controlling bacterial infections (e.g., antibiotic use) may inadvertently alter the gut microbiome in ways that promote viral replication or transmission.

The role of environmental persistence in RbCoV transmission is unknown, but extrapolating from other coronaviruses, it is likely that the virus can survive for days to weeks in cool, moist environments, particularly in organic matter like feces. Biosecurity measures, including all-in/all-out production systems, thorough cleaning and disinfection, and rodent and insect control, are likely critical for breaking the transmission cycle. The identification of chronic carriers [10] presents a particular challenge for eradication, as these animals may serve as a persistent viral reservoir within a herd, seeding new infections in susceptible cohorts.

Zoonotic and Reverse Zoonotic Potential: The Expanding Host Range

Perhaps the most compelling epidemiological development in recent years is the recognition of the rabbit as a potential host for a wide range of coronaviruses, including those of significant public health concern. This has been driven largely by research into SARS-CoV-2. Structural and functional modeling studies have demonstrated that the rabbit angiotensin-converting enzyme 2 (rACE2) receptor, the primary entry point for SARS-CoV-2, shares 85% amino acid identity with the human ortholog and possesses a highly similar 3D structure and electrostatic surface [6]. Crucially, Shi et al. (2023) [7] showed that the receptor-binding domain (RBD) of the SARS-CoV-2 Omicron BA.4/5 variant and its subsequent sub-variants binds to rACE2 with over 10-fold higher affinity compared to the original Wuhan strain. This enhanced binding is mediated in part by a unique glutamine residue at position 34 (Q34) in rACE2 [7]. This finding raises the alarming possibility that rabbits could become infected with SARS-CoV-2 in the field, potentially serving as a new animal reservoir.

This concern is not merely theoretical. A seroprevalence study in wild rabbits has already provided evidence of natural exposure to SARS-CoV-2 [7]. While experimental infections of rabbits with MERS-CoV resulted in high levels of viral RNA shedding from the nose, the animals shed limited amounts of infectious virus and did not transmit the infection to contact animals [11]. This suggests that rabbits may be a "dead-end" host for MERS-CoV, but the situation could be different for the highly adapted Omicron variants. The ability of SARS-CoV-2 to infect rabbits has profound implications for the epidemiology of COVID-19. If rabbits can sustain viral transmission, they could act as a sylvatic reservoir, making global eradication of the virus impossible and facilitating the emergence of new variants that could spill back into humans. The World Health Organization (WHO) and the World Organisation for Animal Health (WOAH) have emphasized the need for surveillance of SARS-CoV-2 in animal populations, and the data on rabbits [6, 7] strongly support their inclusion in these monitoring programs.

Furthermore, the work by So et al. (2019) [9] demonstrating recombination between a rabbit coronavirus (RbCoV-HKU14) and dromedary camel coronavirus HKU23 in Africa is a stark reminder of the role that diverse animal hosts play in coronavirus evolution. This recombination event, identified at the hemagglutinin esterase (HE) gene, could alter the host range, tissue tropism, or pathogenicity of the camel virus. Given that dromedaries are the primary reservoir for MERS-CoV, a zoonotic pathogen with a >30% case fatality rate in humans [8], the introduction of rabbit-derived genetic material into the camel coronavirus gene pool is a significant epidemiological event that warrants continued surveillance. The Centers for Disease Control and Prevention (CDC) and other global health agencies monitor such recombination events as potential precursors to future pandemics.

Experimental Epidemiology: Insights from the Cardiomyopathy Model

A unique and well-characterized epidemiological model exists for a rabbit coronavirus (RbCV) that causes not enteric disease, but a fulminant myocarditis and dilated cardiomyopathy. This work, primarily from the laboratory of Baric and colleagues in the early 1990s [2-4], provides a fascinating counterpoint to the enteric form and offers deep insights into viral pathogenesis and host susceptibility. In this model, infection of laboratory rabbits with a specific RbCV isolate leads to an acute phase (days 2-5) characterized by myocyte necrosis and interstitial edema, followed by a subacute phase (days 6-12) with severe myocarditis, pleural effusion, and congestive heart failure [4]. Remarkably, 41% of surviving animals went on to develop chronic dilated cardiomyopathy, with biventricular dilation, myocyte hypertrophy, and myocardial fibrosis [2].

The epidemiological significance of this model lies in its demonstration of a stark dichotomy in disease outcome. The factors determining whether an infected rabbit dies acutely, develops chronic heart disease, or recovers fully are not fully understood but likely involve a complex interplay of viral strain, host genetics, and immune response. Electrocardiographic (ECG) studies revealed that the acute phase is characterized by sinus tachycardia, depressed QRS voltages, and a high incidence of sudden death, often in the absence of severe clinical signs of heart failure [3]. This suggests that RbCV infection can increase ventricular vulnerability, leading to fatal arrhythmias. This model provides a rare opportunity to study the epidemiology of virus-induced sudden cardiac death, a phenomenon that is difficult to investigate in human populations. The fact that a single viral infection can lead to such divergent outcomes, from asymptomatic infection to acute death to chronic heart failure, highlights the critical importance of host factors in shaping the epidemiology of RbCoV infections. It also underscores the need for strain-level characterization in field studies, as different RbCoV strains may have vastly different tissue tropisms and pathogenic potentials.

Clinical Manifestations and Pathological Lesions

Rabbit coronavirus (RbCoV) infection produces a spectrum of clinical presentations and pathological alterations that are fundamentally dependent upon the viral strain, host age, immune status, and the presence of concurrent enteropathogens. The disease syndromes attributable to RbCoV can be broadly categorized into an enteric form, which is economically devastating in commercial rabbitries, and a cardiac form, which has been characterized experimentally and provides a unique model for virus-induced dilated cardiomyopathy. A critical observation emerging from the literature is that the clinical manifestations of RbCoV are often masked or exacerbated by co-infections with bacterial and parasitic agents, necessitating a nuanced interpretation of field data [1]. This section provides a comprehensive, mechanism-based analysis of the clinical signs and structural lesions associated with RbCoV infection, drawing upon experimental inoculation studies, field outbreak investigations, and comparative pathology with other coronaviruses.

Enteric Syndrome: Clinical Signs and Epidemiological Context

The enteric form of RbCoV infection is most frequently identified in growing rabbits, particularly during the post-weaning period, which is a phase of heightened physiological stress and immunological vulnerability. In a comprehensive epidemiological study conducted across Spanish rabbitries with recurrent enteric problems, Arnal et al. [1] demonstrated a significantly higher prevalence of RbCoV during the growing phase, with a marked association with bacterial agents such as Escherichia coli and Clostridium spiroforme. The clinical presentation is typically non-specific but consistently includes profuse, watery diarrhea, often progressing to dehydration, anorexia, and weight loss. Affected animals frequently exhibit perineal soiling, abdominal distension, and a hunched posture indicative of abdominal pain. Mortality rates in outbreaks can be substantial, particularly when RbCoV acts in concert with other pathogens, contributing to the multifactorial "rabbit enteric syndrome" that plagues the meat rabbit industry worldwide.

The clinical signs of enteric RbCoV infection are a direct consequence of the virus's tropism for the intestinal epithelium, specifically the villous enterocytes of the small intestine and the cecal epithelium. As established in early immunoelectron microscopy studies, viral particles are shed in the feces of both clinically sick and apparently healthy rabbits, indicating the existence of a chronic carrier state that perpetuates viral circulation within a herd [10]. This subclinical shedding is a critical epidemiological feature, as it allows the virus to persist in populations without triggering overt disease until predisposing factors, such as dietary changes, stress, or concurrent infections, precipitate an outbreak. The clinical course can be acute, with death occurring within 24–48 hours of onset, or subacute, with a protracted period of diarrhea and wasting that leads to culling.

Pathological Lesions of the Enteric Form

The gross pathological lesions observed in rabbits succumbing to enteric RbCoV infection are predominantly confined to the gastrointestinal tract. The most consistent finding is severe enteritis and typhlocolitis, characterized by a distended, fluid-filled cecum and proximal colon. The intestinal wall may appear thin and translucent, and the contents are often watery, frothy, or mucoid. Petechial hemorrhages on the serosal surface and within the intestinal lumen are not uncommon, particularly in cases with concurrent clostridial overgrowth [1]. Mesenteric lymph nodes are frequently enlarged and edematous, reflecting a regional immune response.

Histopathological examination reveals the hallmark lesions of coronavirus-induced enteropathy. The intestinal villi are markedly blunted and fused, with significant loss of villous enterocytes at the tips. The remaining enterocytes are often vacuolated, flattened, and show evidence of degeneration and necrosis. The lamina propria is infiltrated by a mixed population of inflammatory cells, including lymphocytes, plasma cells, and macrophages. Importantly, the presence of concurrent pathogens complicates the histological picture; for instance, the detection of Clostridium spiroforme is associated with characteristic spiral-shaped bacteria adhered to the mucosa and the presence of necrotizing colitis [1]. The cecum shows similar changes, with extensive erosion of the cecal tonsil and a loss of lymphoid follicle integrity. The detection of RbCoV antigen via immunohistochemistry (IHC) or qPCR from these lesioned tissues is essential for definitive diagnosis, as the microscopic lesions are not pathognomonic and overlap considerably with other viral and bacterial enteritides [1, 10].

From a mechanistic perspective, the pathogenesis mirrors that of other enteric coronaviruses, such as transmissible gastroenteritis virus (TGEV) of swine and bovine coronavirus (BCoV). The primary insult is the lysis of mature, absorptive enterocytes at the villous tips, which directly reduces the intestinal absorptive surface area and disrupts the brush-border enzyme activity essential for digestion. The resultant malabsorptive diarrhea is compounded by crypt cell hyperplasia and secretory mechanisms triggered by the inflammatory response. The loss of the epithelial barrier also facilitates the translocation of bacteria and their toxins, leading to septicemia and the systemic inflammatory response syndrome (SIRS), which ultimately drives mortality.

Cardiac Syndrome: Clinical Manifestations in the Experimental Model

A dramatically different clinical syndrome was identified in an experimental model of RbCoV infection, originally described by Edwards et al. and Alexander et al. [2, 4]. In this model, infection of laboratory rabbits with a specific strain of RbCoV resulted in a biphasic disease culminating in myocarditis, congestive heart failure, and dilated cardiomyopathy. The clinical course is divided into acute (days 2–5 post-infection) and subacute (days 6–12) phases. During the acute phase, animals often die suddenly without premonitory signs, which is highly suggestive of a fatal cardiac arrhythmia rather than respiratory failure. Serial electrocardiographic (ECG) monitoring during this phase reveals sinus tachycardia, depressed R- and T-wave voltages, and a spectrum of conduction defects, including atrial and ventricular premature complexes, idioventricular rhythms, and transient atrioventricular blocks [3]. The investigators posited that RbCoV infection increases ventricular vulnerability, making these rabbits a rare model for studying sudden cardiac death in the context of viral myocarditis.

In animals surviving the acute phase, the subacute phase is characterized by clinical signs of biventricular congestive heart failure. These include tachypnea, lethargy, cyanosis of the mucous membranes, and the development of pleural effusion and pulmonary congestion [4]. Hepatomegaly and ascites are also observed. Remarkably, a long-term follow-up study revealed that 41% of survivors progressed to a chronic state of dilated cardiomyopathy, with evidence of reduced systolic function, biventricular dilation, and myocyte hypertrophy [2]. These rabbits exhibited persistent increases in heart weight-to-body weight ratios, mimicking the human condition of post-myocarditic cardiomyopathy.

Pathological Lesions of the Cardiac Form

The pathological lesions in the cardiac form are striking and occur in the absence of significant gastrointestinal pathology, suggesting a distinct viral tropism or host response. Grossly, the hearts of infected rabbits in the acute and subacute phases are pale, flabby, and exhibit biventricular dilation, with the right ventricle being affected earlier and more severely than the left [4]. Pleural effusion (often serosanguinous) and pulmonary edema are consistent findings, along with passive congestion of the liver and spleen.

Histopathologically, the acute phase (days 2–5) is dominated by degeneration and necrosis of individual myocytes, myocytolysis, interstitial edema, and hemorrhage [4]. These lesions are multifocal and randomly distributed, often with a predilection for the papillary muscles and the subendocardial region. The inflammatory infiltrate is initially minimal, but by day 9, a robust lymphocytic and histiocytic myocarditis is evident, which peaks by day 12. The inflammation is associated with the presence of viral antigen, as confirmed by virus isolation from cardiac tissue [4]. In the chronic phase, the necroinflammatory lesions are replaced by interstitial and replacement fibrosis, particularly severe in the papillary muscles, and myocyte hypertrophy [2]. These fibrotic changes are the structural substrate for the persistent diastolic and systolic dysfunction observed in the dilated cardiomyopathy phenotype. The ECG abnormalities noted, prolonged QTc intervals, ST-segment changes, and ventricular arrhythmias, correlate directly with the extent of myocardial fibrosis and the disruption of the conducting system [3].

The mechanism by which RbCoV induces myocardial damage is likely a combination of direct viral cytopathic effect and immune-mediated injury. The presence of viral RNA in the myocardium during the acute phase supports direct cell lysis. However, the peak of inflammation coinciding with the adaptive immune response suggests that cytotoxic T lymphocytes and pro-inflammatory cytokines contribute significantly to the subsequent fibrosis and remodeling. This biphasic pathogenesis is analogous to that seen in human coxsackievirus myocarditis and certain cases of SARS-CoV-2-associated myocarditis, where the initial viral insult is followed by a dysregulated immune response that perpetuates cardiac injury.

Potential for Respiratory and Systemic Involvement

While the enteric and cardiac forms are best characterized, the potential for respiratory tract involvement in RbCoV should not be dismissed. Comparative genomic analyses have revealed that rabbit coronavirus HKU14 shares recombination events with dromedary camel coronavirus HKU23 and rodent coronaviruses, indicating a capacity for genetic plasticity that could alter tissue tropism [9]. Furthermore, studies on the structure of rabbit angiotensin-converting enzyme 2 (ACE2) have demonstrated an 85% identity with human ACE2 and a high degree of similarity in electrostatic and thermodynamic properties, confirming the rabbit as a suitable model for studying coronavirus entry and pathogenesis [6, 7]. In the context of field outbreaks of rabbit enteric syndrome, respiratory signs are occasionally reported but are rarely the primary clinical feature. It is plausible that respiratory disease is underdiagnosed, particularly in the presence of concurrent pasteurellosis or bordetellosis.

Systemic lesions, such as splenic atrophy, lymph node depletion, and hepatic degeneration, have been noted in severe cases of the enteric syndrome [1]. These are likely secondary to the profound dehydration, metabolic acidosis, and endotoxemia resulting from the breakdown of the intestinal mucosal barrier. In the cardiac model, the systemic lesions of congestive heart failure (pulmonary edema, hepatic congestion) are direct consequences of pump failure [4]. The detection of viral antigens in macrophages and other cell types in some experimental models raises the possibility of a broader cellular tropism than currently appreciated.

From a diagnostic and regulatory perspective, the role of RbCoV in rabbit enteric syndrome has significant implications for the rabbit meat industry, which is subject to monitoring by organizations such as the World Organisation for Animal Health (WOAH) for notifiable diseases. The high prevalence of RbCoV in farms with recurrent enteric problems, coupled with its frequent co-detection with WOAH-listed bacterial pathogens, underscores the need for comprehensive diagnostic profiles that include this virus [1]. The development and validation of sensitive and specific diagnostic tools, such as quantitative real-time PCR (qPCR) and immunohistochemistry (IHC) using antibodies raised in rabbits against viral nucleocapsid or spike proteins, are essential for accurate disease surveillance and the implementation of effective biosecurity and vaccination strategies [8, 15, 27].

Diagnostic Approaches for Rabbit Coronavirus

The accurate and timely diagnosis of Rabbit Coronavirus (RbCoV) is a complex endeavor, fraught with challenges that stem from the virus's multifactorial etiology, its propensity for subclinical persistence, and the frequent occurrence of co-infections with other enteric pathogens. The diagnostic landscape for RbCoV must therefore be considered within the broader context of the rabbit enteric syndrome, a condition consistently demonstrated to involve a consortium of viral, bacterial, and parasitic agents [1]. A robust diagnostic strategy is not merely a matter of pathogen detection; it requires a comprehensive, multi-modal approach that integrates molecular, serological, antigenic, and pathological findings to ascertain the true clinical significance of RbCoV in both individual cases and within the epidemiological framework of a rabbitry.

Molecular Detection: The Cornerstone of RbCoV Diagnosis

Nucleic acid amplification techniques, particularly quantitative real-time reverse transcription polymerase chain reaction (RT-qPCR), represent the gold standard for the direct detection of RbCoV RNA. The seminal work by Arnal et al. [1] established a critical baseline for this approach by employing qPCR to detect RbCoV and lapine bocaparvovirus (LBoV) in Spanish rabbitries, using cycle quantification (Cq) values to support the implication of these viruses in digestive disorders. The very presence of detectable viral RNA, and especially the magnitude of the Cq values, provided a semi-quantitative link between viral load and clinical disease [1]. The design of such assays often targets conserved regions of the coronavirus genome, such as the replicase gene (e.g., ORF1ab) or the nucleocapsid (N) gene, which is a highly abundant and immunodominant protein. The development of specific PCR primers for the distinct rabbit CoV HKU14 strain, as part of the broader phylogenetic studies of embecoviruses, is essential for differentiating RbCoV from other betacoronaviruses that may infect lagomorphs or co-circulate in multi-species environments [9].

The diagnostic utility of RT-qPCR, however, is nuanced. As demonstrated in studies on MERS-CoV and SARS-CoV-2, the mere presence of viral RNA does not necessarily equate to the presence of infectious virus or clinical disease. Research on MERS-CoV in rabbits showed that while high levels of viral RNA were shed from the nasal epithelium following inoculation, the animals shed only limited amounts of infectious virus, a discrepancy that explained the lack of transmission [11]. This phenomenon, where RT-qPCR detects non-infectious or degraded RNA, is a critical caveat for the interpretation of positive results in asymptomatic or convalescent rabbits. Therefore, a positive RT-qPCR result for RbCoV must be interpreted in the context of clinical signs, histopathology, and ideally, quantitative viral loads. The use of RT-qPCR is also fundamental for epidemiological surveillance, allowing for the detection of viral shedding across different age groups, with studies showing a higher prevalence of RbCoV during the growing phase [1]. Furthermore, the technology provides a platform for phylogenetic and recombination analyses, which are vital for understanding the evolutionary dynamics and interspecies transmission potential of rabbit coronaviruses, as exemplified by the detection of recombinant fragments of RbCoV-HKU14 in the genomes of dromedary camel coronaviruses [9].

Serological Assays for Antibody Detection

Serological testing provides a retrospective view of infection history and is an indispensable tool for epidemiological surveys and vaccine efficacy studies. The development of these assays for RbCoV has, to a large extent, been informed by the extensive work on other coronaviruses, including SARS-CoV, MERS-CoV, and bovine coronavirus (BCoV).

Indirect Enzyme-Linked Immunosorbent Assay (iELISA): The most common serological format is the indirect ELISA, which detects the presence of anti-RbCoV antibodies in serum or plasma. The selection of the antigen is critical. The nucleocapsid (N) protein is a prime candidate due to its high expression during infection and its relative conservation among coronaviruses. For instance, an iELISA for BCoV was successfully established using a recombinant N protein expressed in CHO cells, with rabbit polyclonal antibodies serving as critical reagents for quality control [5]. A similar approach, using the N protein of RbCoV, could be adapted for rabbit diagnostics. However, one must be cautious of cross-reactivity. While rabbit antisera against SARS-CoV N protein were shown to cross-react with specific epitopes [28, 31], the potential for cross-reactivity between RbCoV and other rabbit pathogens or vaccine antigens must be rigorously evaluated. Studies on other coronaviruses have demonstrated that iELISA can be highly specific, with no cross-reaction against heterologous viruses [5].

Protein Microarray and Competition ELISA: More sophisticated serological methods, such as protein microarrays, allow for the simultaneous profiling of antibodies against multiple viral proteins. This approach was used to map the immunodominant regions of SARS-CoV S and N proteins across multiple species, including rabbits, revealing that fragments S3 (aa 402–622) and N4 (aa 220–336) were the most broadly reactive [24]. This suggests that recombinant proteins representing these conserved regions of the RbCoV S and N proteins would be ideal antigens for a multi-species or rabbit-specific diagnostic test. Furthermore, competition ELISAs, which use a specific monoclonal antibody to block binding of serum antibodies, can provide a highly specific means of detecting seroconversion, particularly when distinguishing between closely related coronaviruses [24]. These assays offer a significant advantage in minimizing cross-reactivity.

Virus Neutralization Test (VNT): While not as high-throughput as ELISA, the VNT remains the gold standard for detecting functional, neutralizing antibodies. The presence of neutralizing antibodies is a direct correlate of protective immunity. The generation of rabbit antisera with potent neutralizing activity against SARS-CoV has been well documented, with a single immunization with a receptor-binding domain (RBD) fusion protein inducing antibody titers capable of completely inhibiting viral infection at a serum dilution of 1:10,240 [25]. For RbCoV, the VNT can be performed using cell culture-adapted virus isolates (if available) or pseudotyped virus systems. The latter, using lentiviral or VSV-based pseudotypes bearing the RbCoV spike protein, offers a safer, more high-throughput alternative that does not require live wild-type virus.

Antigen Detection: Direct Identification of Viral Proteins

The direct detection of viral antigens in tissues or excreta provides a rapid and clinically relevant diagnosis, circumventing the need for specialized molecular equipment in some instances.

Immunohistochemistry (IHC) and Immunofluorescence Assay (IFA): These techniques are invaluable for localizing viral antigen within specific cell types in formalin-fixed paraffin-embedded (FFPE) tissues, linking viral presence to histopathological lesions. Rabbit polyclonal antibodies against the SARS-CoV N protein have been extensively used for IHC and IFA to detect the virus in human lung autopsy tissues, revealing infection of pneumocytes and ciliated airway cells during the acute phase of lung injury [27, 29, 30]. The cross-reactivity of such antibodies with other coronaviruses, including the ability of a rabbit anti-SARS-CoV 3CLpro antiserum to detect the highly conserved 3CLpro of SARS-CoV-2, suggests that carefully selected polyclonal antibodies raised against conserved proteins of RbCoV could be used to detect the virus in rabbit intestinal or cardiac tissues [26]. In the context of rabbit enteric coronavirus, IHC could confirm the presence of viral antigen within the cytoplasm of enterocytes, thereby establishing a causal link between the detected virus and the observed villous atrophy or necrosis.

Immunoelectron Microscopy (IEM): Historically, IEM was one of the first techniques used to identify a rabbit enteric coronavirus (RECV) [10]. This method offers the unique advantage of confirming the morphological identity of a suspected coronavirus particle, as the antibody (e.g., guinea pig anti-RECV immune serum) will specifically aggregate the virions, distinguishing them from other virus-like particles in fecal samples. IEM was shown to be more sensitive than direct EM for detecting RECV and was instrumental in identifying chronic carriers of the virus [10]. While labor-intensive and requiring highly specialized equipment, IEM remains a definitive validation tool.

Lateral Flow Immunochromatographic Assays (LFIAs) and Point-of-Care Tests: The need for rapid, field-deployable diagnostics is acute for managing outbreaks in commercial rabbitries. LFIAs, similar to those developed for human coronaviruses, offer a promising avenue. For example, a rapid antigen detection assay for MERS-CoV was shown to have 100% specificity and 91.7% sensitivity and did not cross-react with rabbit CoV HKU14 [8]. This indicates that a highly specific assay can be developed. The development of an LFIA for RbCoV would require the production of high-affinity monoclonal antibodies (mAbs) against the RbCoV N protein. The successful generation of rabbit mAbs for the detection of SARS-CoV-2 N protein demonstrates the feasibility of this approach [28]. More advanced platforms, such as upconversion nanoparticle-based LFIAs (UCNP-LFIA), can achieve exceptionally high sensitivity, with limits of detection for the SARS-CoV-2 N protein as low as 3.59 pg/mL and a 100-fold improvement over traditional colloidal gold LFIAs [15]. Analogous development for RbCoV would revolutionize point-of-care diagnostics in the field.

The Role of Co-infections and the Need for Multiplex Diagnostics

A critical lesson from the literature is that enteric disease in rabbits is overwhelmingly multifactorial [1]. Arnal et al. [1] consistently detected RbCoV alongside LBoV, Escherichia coli, Clostridium spiroforme, and various parasites. Therefore, any diagnostic approach aimed at a single pathogen is fundamentally incomplete. The field must move towards multiplex molecular panels that can simultaneously detect RbCoV, LBoV, rotavirus, and key bacterial and parasitic agents. The development of such assays, perhaps using a multiplex RT-qPCR or a next-generation sequencing-based metagenomic approach, is the single most important advancement needed for a holistic understanding of rabbit enteric syndrome.

For example, research on other coronaviruses has shown that the double-antibody sandwich ELISA (DAS-ELISA) for swine acute diarrhea syndrome coronavirus (SADS-CoV) achieved a 93.93% coincidence rate with RT-PCR [32]. A similar approach, incorporating mAbs specific for RbCoV and LBoV, could form the basis of a rapid, high-throughput antigen detection panel. Furthermore, the interpretation of diagnostic results must be hierarchical. Detection of RbCoV in a healthy rabbit without histopathological changes is likely an incidental finding or a sign of a subclinical carrier state. In contrast, detection of the virus in a young rabbit with severe enteritis, concurrent villous atrophy, and the presence of other pathogens requires a different clinical interpretation, viewing RbCoV as a key component of a polymicrobial disease complex.

Co-infections and Multifactorial Enteric Disease

The etiopathogenesis of enteric disease in commercial rabbitries represents a paradigm of multifactorial complexity, wherein rabbit coronavirus (RbCoV) does not act as a solitary pathogen but rather operates within a dynamic consortium of viral, bacterial, and parasitic agents. This intricate interplay, often termed "Rabbit Enteric Syndrome" (RES), has confounded diagnosticians and producers for decades, as the clinical presentation, ranging from mild diarrhea to fatal enterocolitis, rarely conforms to a monomicrobial etiology. The recognition that RbCoV is a consistent but not exclusive component of these outbreaks has fundamentally reshaped our understanding of disease causation, moving the field away from simplistic Koch’s postulates toward a systems-level appreciation of microbial synergism, host susceptibility, and environmental modulation.

The Virological Foundation: RbCoV and Lapine Bocaparvovirus (LBoV)

The seminal work of Arnal et al. (2025) in Spanish rabbitries has provided the most comprehensive epidemiological and pathological evidence to date for the synergistic role of RbCoV and lapine bocaparvovirus (LBoV) in enteric disease [1]. In their detection frequency study, which employed quantitative PCR (qPCR) on samples from both clinically affected and apparently healthy animals on farms with recurrent enteric problems, the authors demonstrated that the presence and cycle quantification (Cq) values for both viruses supported their active involvement in digestive pathology. Critically, the study revealed that these viruses were consistently detected in farms with endemic enteric issues, but rarely in isolation; in the vast majority of cases, they were found in association with other bacterial and parasitic agents [1]. This observation is not merely an epidemiological curiosity but a mechanistic clue: the viral infection likely creates a permissive environment for secondary invaders, either through direct disruption of the intestinal epithelial barrier, immunomodulation, or alteration of the gut microbiome.

The lesional study component of Arnal et al. provided histopathological corroboration, confirming the presence of lesions characteristic of both RbCoV and LBoV infection, including villous atrophy, crypt hyperplasia, and lymphoplasmacytic infiltration. However, the authors were careful to note that these lesions were frequently exacerbated by the concurrent presence of other viral, bacterial, and parasitic agents [1]. This finding aligns with the broader veterinary literature on coronavirus enteropathies, where co-infections are the rule rather than the exception. For instance, in bovine coronavirus (BCoV) infections, concurrent infections with rotavirus, Cryptosporidium parvum, and enterotoxigenic Escherichia coli are well-documented to increase disease severity and mortality, a pattern that appears to be recapitulated in the rabbit [5, 33, 34].

Bacterial Synergists: Escherichia coli and Clostridium spiroforme

The epidemiological study by Arnal et al. (2025) specifically examined age-related prevalence and co-infection patterns, revealing a higher prevalence of RbCoV and LBoV during the growing phase (post-weaning to market age). This period is notoriously vulnerable to enteric disease due to the waning of maternal immunity, the stress of dietary transition, and the establishment of a mature gut microbiota. The authors identified a statistically significant association between the presence of these viruses and two bacterial pathogens: Escherichia coli and Clostridium spiroforme [1]. This association is biologically plausible and clinically ominous.

Enteropathogenic E. coli (EPEC) strains are known to produce attaching and effacing (A/E) lesions in the rabbit intestine, a pathology that can be potentiated by viral co-infection. The mechanism likely involves viral-induced disruption of the glycocalyx and tight junction proteins, exposing basolateral receptors for bacterial adhesion. Similarly, C. spiroforme is a toxigenic clostridium that produces an iota-like toxin responsible for severe, often fatal, enterotoxemia in rabbits. The question of causality, whether viral infection predisposes to clostridial overgrowth or whether clostridial toxins exacerbate viral replication, remains unresolved, but the epidemiological linkage is robust. The World Organisation for Animal Health (WOAH) has long recognized that enteric disease in rabbits is a multifactorial syndrome, and the data from Arnal et al. provide the molecular evidence to support this classification, suggesting that diagnostic panels for rabbit enteric disease should routinely include both RbCoV and LBoV alongside bacterial targets [1].

The Role of Parasitic Co-factors and the Microbiome

Beyond bacteria, the parasitic burden in affected rabbitries cannot be ignored. Coccidiosis, caused by Eimeria species, is a pervasive problem in intensive rabbit production and is known to cause significant intestinal damage, particularly in the ileum and cecum. The co-occurrence of RbCoV with Eimeria spp. has been anecdotally reported, and the synergistic potential is substantial: coccidial infection disrupts the epithelial barrier and induces a Th2-biased immune response, which may be permissive for coronavirus replication. Conversely, coronavirus-induced immunosuppression may allow for subclinical coccidial infections to flare into clinical disease. The study by Arnal et al. did not specifically quantify parasitic burdens in their co-infection analysis, but they acknowledged that parasitic agents were among the "other agents" that may have exacerbated the condition [1]. Future studies employing metagenomic sequencing of the gut microbiome and parasitome will be essential to disentangle these interactions.

The gut microbiome itself is likely a critical, yet understudied, variable in the RbCoV co-infection paradigm. Coronaviruses, including murine hepatitis virus (MHV) and transmissible gastroenteritis virus (TGEV) of swine, are known to alter the composition of the intestinal microbiota, often leading to dysbiosis characterized by a bloom of Proteobacteria and a reduction in beneficial Firmicutes and Bacteroidetes. This dysbiosis can, in turn, promote the overgrowth of opportunistic pathogens like E. coli and Clostridium spp., creating a self-reinforcing cycle of inflammation and disease. The rabbit cecum, a specialized fermentation vat, is particularly sensitive to such disruptions. The presence of RbCoV may disrupt the delicate pH and volatile fatty acid profile of the cecum, favoring the proliferation of toxigenic clostridia. This hypothesis is supported by the observation that C. spiroforme outbreaks in rabbits are often precipitated by stressors such as diet change or antibiotic use, and viral infection may act as an analogous trigger.

Diagnostic and Economic Implications for the Rabbit Meat Industry

The economic impact of multifactorial enteric disease on the rabbit meat industry is staggering, representing one of the most significant causes of morbidity, mortality, and antimicrobial use. The findings of Arnal et al. have direct implications for diagnostic strategies. The authors explicitly recommend the inclusion of RbCoV and LBoV in the "diagnostic enteric profile for rabbits" [1]. This is a paradigm shift from traditional diagnostics, which have historically focused on bacterial culture and parasitology. The adoption of multiplex qPCR panels that simultaneously detect RbCoV, LBoV, E. coli virulence genes, C. spiroforme toxin genes, and Eimeria species would provide a more holistic picture of the etiological agents at play. Such panels are already in use for other livestock species (e.g., bovine respiratory disease complex) and are now urgently needed for rabbits.

Furthermore, the multifactorial nature of the disease demands a multifactorial intervention strategy. As Arnal et al. state, "digestive disorders should be considered a multifactorial condition that requires interventions on multiple fronts, including pathogen control and a thorough review of management and environmental practices" [1]. This implies that vaccination against RbCoV alone, while potentially beneficial, is unlikely to be a silver bullet. Control programs must also address biosecurity to reduce the introduction of LBoV and bacterial pathogens, optimize nutrition to support gut health, manage coccidial burdens through strategic anticoccidial use, and minimize environmental stressors such as temperature fluctuations and overstocking. The Food and Agriculture Organization of the United Nations (FAO) has emphasized the importance of such integrated approaches for sustainable livestock production, and the rabbit industry would be well-served to adopt these principles.

Broader Context: Lessons from Other Coronavirus Systems

The co-infection dynamics observed with RbCoV are not unique but rather reflect a common theme in coronavirus biology. In swine, porcine epidemic diarrhea virus (PEDV) frequently co-infects with porcine deltacoronavirus (PDCoV) and rotavirus, leading to "porcine enteric disease complexes" that are far more severe than any single infection [32]. In cattle, BCoV is a component of the bovine respiratory disease complex and is often found in concert with Mannheimia haemolytica, Pasteurella multocida, and Mycoplasma bovis [5]. The molecular mechanisms underlying these synergies are beginning to be elucidated. For example, coronavirus infection can upregulate the expression of host cell receptors for bacterial adhesins, or it can suppress the expression of antimicrobial peptides, thereby lowering the threshold for bacterial invasion.

In the context of rabbit health, the work of Descôteaux et al. (2005) using immunoelectron microscopy (IEM) demonstrated that RbCoV could be detected in both sick and healthy rabbits, highlighting the existence of chronic carriers [10]. This finding is critical for understanding co-infection dynamics: healthy carriers may serve as a reservoir of RbCoV that, under conditions of stress or co-infection with another pathogen, can be shed in higher quantities and trigger clinical disease in susceptible cohorts. This carrier state complicates control efforts, as clinically normal animals may still be contributing to environmental contamination.

Zoonotic Considerations and the Expanding Host Range

While the primary focus of this section is on enteric disease in rabbits, the broader context of coronavirus host range and recombination is relevant. The work of So et al. (2019) on dromedary camel coronavirus HKU23 revealed that recombinant fragments of RbCoV-HKU14 were identified at the hemagglutinin esterase (HE) gene position in African camel coronaviruses [9]. This finding demonstrates that RbCoV has the capacity to recombine with other betacoronaviruses, potentially contributing to the emergence of novel viruses with altered tissue tropism or host range. The Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO) have highlighted the importance of surveillance for coronavirus recombination events in animal reservoirs, as these events can precede zoonotic spillover. Although there is no evidence that RbCoV is zoonotic, its genetic material has been found in other species, underscoring the interconnectedness of coronavirus ecology.

Furthermore, the structural studies by Shi et al. (2023) demonstrated that rabbit ACE2 has a uniquely high binding affinity for the Omicron BA.4/5 variant of SARS-CoV-2, mediated in part by the Q34 residue [7]. This finding, while not directly related to RbCoV enteric disease, raises the possibility that rabbits could serve as a mixing vessel for coronaviruses, where enteric and respiratory strains could recombine. The potential for such events to generate novel pathogens with altered tropism (e.g., a respiratory coronavirus acquiring enteric pathogenicity factors, or vice versa) is a theoretical but not implausible risk that warrants continued surveillance.

In summary, the evidence overwhelmingly supports the classification of RbCoV-associated enteric disease as a multifactorial syndrome. The virus is a consistent and important component, but it operates within a complex ecosystem of co-infecting pathogens, host factors, and environmental pressures. The diagnostic and therapeutic approach must therefore be equally complex, moving beyond single-pathogen thinking toward a systems-based strategy that addresses the entire microbial community and the management practices that shape it.

Prevention, Control, and Biosecurity Strategies

The Multifactorial Nature of Rabbit Coronavirus Disease and Implications for Control

The prevention and control of rabbit coronavirus (RbCoV) infection must be approached with a profound appreciation for the complex, multifactorial etiology of enteric disease in commercial rabbitries. As demonstrated by Arnal et al. [1], RbCoV is rarely, if ever, a sole pathogen; rather, it operates within a pathogenic consortium that includes lapine bocaparvovirus (LBoV), bacterial agents such as Escherichia coli and Clostridium spiroforme, and various parasitic organisms. This ecological reality dictates that biosecurity strategies cannot be unidimensional. Effective control mandates a holistic, multi-front intervention that simultaneously addresses pathogen reduction, environmental management, and the optimization of host resistance. The consistent detection of RbCoV in farms with recurrent enteric problems, coupled with its higher prevalence during the growing phase [1], underscores a critical window of vulnerability that must be targeted by management protocols. The growing phase represents a period of immunological naivety, physiological stress from weaning, and dietary transition, all of which converge to create a permissive environment for viral amplification and clinical expression. Therefore, control strategies must be temporally stratified, with intensified biosecurity measures applied during the post-weaning and early fattening periods.

Fundamental Biosecurity Architecture for RbCoV Management

Physical Barriers and Zoning

The foundational principle of RbCoV biosecurity is the establishment of robust physical and operational barriers that prevent the introduction and dissemination of the virus. Given that RbCoV is shed in high concentrations in the feces of infected rabbits, both clinically ill and subclinically shedding carriers [10], the primary vectors of transmission are fomites, contaminated equipment, footwear, clothing, and personnel movement. Commercial rabbitries must implement a clear zoning system, demarcating a "clean" area (breeding and young stock) from a "dirty" area (fattening units and quarantine facilities). The use of dedicated footwear, coveralls, and hand-washing stations at zone transitions is non-negotiable. Footbaths containing virucidal disinfectants (e.g., accelerated hydrogen peroxide, sodium hypochlorite, or peracetic acid-based compounds) must be maintained at all entry points and changed at least daily, as organic matter rapidly inactivates many disinfectants. The design of facilities should facilitate an all-in/all-out (AIAO) management system, particularly for fattening units. AIAO allows for complete depopulation, thorough cleaning, disinfection, and a downtime period (ideally 7–14 days) before repopulation, thereby breaking the cycle of continuous viral circulation that is characteristic of continuously stocked barns. This is critical because RbCoV, like other coronaviruses, can persist in the environment, particularly in organic material, and AIAO is the only reliable method to eliminate residual contamination.

Quarantine and Acclimation Protocols

The introduction of replacement breeding stock represents one of the highest-risk activities for introducing novel RbCoV strains into a naïve herd. A mandatory quarantine period of at least 30 days, housed in a physically separate facility, is essential. During this period, animals should be monitored daily for clinical signs of enteric or respiratory disease. Diagnostic testing, using quantitative PCR (qPCR) for RbCoV on pooled fecal samples [1], should be performed upon arrival and again before release from quarantine. Serological testing, while less common for RbCoV, could be developed using indirect ELISA methods analogous to those established for bovine coronavirus (BCoV) using recombinant nucleocapsid (N) protein [5] or for SARS-CoV-2 using the receptor-binding domain (RBD) [25]. However, the utility of serology for individual animal management is limited by the lag time between infection and seroconversion. The primary goal of quarantine is to prevent the introduction of actively shedding animals. Furthermore, acclimation, the controlled exposure of incoming stock to the resident farm microbiota, may be considered, but this must be done cautiously and under veterinary supervision to avoid overwhelming naïve animals with pathogenic strains.

Environmental and Management Controls

Hygiene and Sanitation Protocols

The physical environment of a rabbitry is a reservoir for RbCoV. Cages, feeders, and drinkers must be constructed of non-porous materials that can withstand rigorous cleaning and disinfection. The cleaning protocol must follow a strict sequence: dry removal of all organic matter (bedding, feces, feed), followed by a pre-wash with a detergent to break down biofilms, a rinse, application of a licensed virucidal disinfectant with a validated contact time (typically 10–30 minutes), and a final rinse to remove chemical residues. The choice of disinfectant is critical. Coronaviruses are enveloped viruses and are generally susceptible to lipid solvents, but efficacy is heavily dependent on the absence of organic load. Accelerated hydrogen peroxide (0.5%) and sodium hypochlorite (0.1% available chlorine) are effective, but quaternary ammonium compounds may have variable activity against coronaviruses in the presence of organic matter. The ventilation system must be designed to minimize ammonia levels, as ammonia is a potent mucosal irritant that damages the respiratory and enteric epithelium, increasing susceptibility to viral infection and secondary bacterial invasion. High stocking densities must be avoided, as they promote stress, increase the fecal-oral contact rate, and facilitate the rapid spread of RbCoV. The epidemiological data showing a significant association between RbCoV and Clostridium spiroforme [1] highlights the importance of dietary management. High-starch, low-fiber diets can predispose rabbits to clostridial overgrowth, and this dysbiosis can exacerbate coronavirus-induced enteritis. Therefore, nutritional strategies that promote a stable cecal microbiome, such as providing adequate levels of indigestible fiber and avoiding sudden feed changes, are an integral component of disease control.

Vector and Pest Control

Rodents, flies, and other pests can serve as mechanical vectors for RbCoV, transporting the virus from contaminated areas to clean ones. A rigorous, integrated pest management program is essential. This includes sealing entry points, maintaining a clean perimeter free of debris and standing water, using bait stations and traps, and, where necessary, employing insecticidal fogging. While rabbits are the primary host, the potential for fomite transmission via human handlers, veterinarians, and service personnel cannot be overstated. Strict protocols for visitor access, including the use of disposable coveralls and boots, must be enforced.

Diagnostic Surveillance and Early Detection

The Role of Molecular Diagnostics

The cornerstone of an effective control program is the ability to detect RbCoV early, before clinical outbreaks become severe. As demonstrated by Arnal et al. [1], qPCR is a highly sensitive tool for detecting RbCoV RNA in fecal samples, even in subclinically shedding animals. Routine surveillance should involve the collection of pooled fecal samples from different age groups (does, weanlings, fatteners) on a weekly or bi-weekly basis. The Cq (quantification cycle) values obtained from qPCR provide valuable information. Low Cq values (high viral RNA load) in a sample from a healthy pen may be an early warning sign of an impending outbreak, allowing for preemptive intervention (e.g., enhanced hygiene, separation of affected groups). The inclusion of RbCoV in the diagnostic enteric profile, as advocated by Arnal et al. [1], is a critical step forward for the industry. The development of rapid antigen detection tests, such as immunochromatographic assays (lateral flow devices), analogous to those developed for MERS-CoV [8] or canine brucellosis [12], would be a game-changer for on-farm diagnosis. Such tests, targeting the N protein, could provide results in 15–30 minutes, enabling immediate decision-making regarding isolation and treatment. The success of a colloidal gold-based test for canine coronavirus [12] suggests that a similar approach for RbCoV is technically feasible and would be highly valuable for resource-limited settings.

Necropsy and Histopathological Examination

When mortality occurs, a thorough post-mortem examination is indispensable. Gross lesions, such as fluid-filled, dilated ceca and hemorrhagic enteritis, are suggestive but not pathognomonic. Histopathological examination can reveal characteristic lesions, including villous atrophy, crypt hyperplasia, and syncytial cell formation in the intestinal epithelium. Immunohistochemistry (IHC) using rabbit polyclonal or monoclonal antibodies against RbCoV N protein can confirm the presence of viral antigen within lesioned tissues, providing definitive evidence of viral involvement. The use of IHC has been instrumental in understanding the pathogenesis of SARS-CoV-2 in human tissues [27, 29] and can be directly adapted for RbCoV. The detection of viral RNA by RNAscope in situ hybridization (ISH) on formalin-fixed, paraffin-embedded (FFPE) tissues [27] offers another layer of diagnostic precision, allowing for the spatial localization of viral replication within the tissue architecture.

Vaccination and Immunoprophylaxis

Current Status and Future Directions

Currently, there is no commercially available vaccine specifically for RbCoV. This represents a significant gap in the control armamentarium. However, the extensive literature on coronavirus vaccinology, particularly for SARS-CoV-2, porcine epidemic diarrhea virus (PEDV), and transmissible gastroenteritis virus (TGEV), provides a robust framework for developing an RbCoV vaccine. The spike (S) protein, particularly its receptor-binding domain (RBD), is the primary target for neutralizing antibodies. Studies on SARS-CoV have demonstrated that the RBD of the S protein is a critical neutralization determinant and that antibodies targeting this region can potently inhibit viral entry [20, 25]. A subunit vaccine based on the RbCoV RBD, expressed in a recombinant system and formulated with an appropriate adjuvant, would be a logical candidate. The immunogenicity of such a construct could be evaluated in rabbits using an ELISA based on the N protein [5] or the S protein [24] to measure antibody titers, and neutralization assays (e.g., pseudovirus-based assays [20]) to assess functional antibody responses.

Alternatively, a DNA vaccine approach, similar to the ZyCoV-D vaccine for SARS-CoV-2 [35], could be explored. This platform offers advantages in terms of rapid development, thermostability, and the ability to induce both humoral and cellular (Th1) immune responses. The induction of a strong cell-mediated immune response, particularly CD8+ T cells, is important for clearing virus-infected cells and may be critical for controlling chronic or persistent infections. The use of anti-idiotypic antibodies, as demonstrated for murine hepatitis virus (MHV) [36], represents a more experimental but conceptually elegant approach. This strategy uses antibodies that mimic the structure of a viral epitope to induce a protective immune response without exposing the animal to the live virus. While not yet a practical solution for RbCoV, it highlights the breadth of immunological strategies available.

Passive Immunization

In an outbreak scenario, passive immunization with hyperimmune serum or colostrum could provide immediate, short-term protection. This approach has been used successfully for TGEV in piglets, where colostral IgA provides lactogenic immunity [38]. For rabbits, the administration of polyclonal antibodies raised in rabbits or other species (e.g., goats) against RbCoV S or N proteins could be used to treat or prevent infection in high-value animals or in neonates. However, the practical challenges of producing and administering such sera on a large scale are considerable. The use of recombinant single-chain variable fragments (scFvs) [37] offers a more standardized and scalable alternative, although their rapid in vivo clearance (half-life of ~6 minutes) presents a significant limitation that would require strategies to improve stability, such as PEGylation or fusion to an Fc domain.

Regulatory and Industry-Level Considerations

Adherence to International Standards

The World Organisation for Animal Health (WOAH) provides guidelines for the control of transmissible animal diseases, including enteric coronaviruses. While RbCoV is not currently listed as a notifiable disease by WOAH, the principles of biosecurity, surveillance, and reporting are universally applicable. National veterinary authorities should consider establishing surveillance programs for RbCoV in commercial rabbitries, particularly in regions with a high density of rabbit meat production, such as Spain, France, Italy, and China. The economic impact of RbCoV-associated enteric disease, as highlighted by Arnal et al. [1], justifies a coordinated industry response. This could include the development of a voluntary certification program for farms that adhere to a defined set of biosecurity standards, analogous to programs for Salmonella control in poultry.

The Role of the Rabbit as a Model and a Risk

It is critical to acknowledge the dual role of the rabbit in coronavirus research and epidemiology. The rabbit has been extensively used as an animal model for human coronavirus diseases, including SARS-CoV-2 [6, 7, 17] and MERS-CoV [11]. The high structural and electrostatic similarity between rabbit and human ACE2 [6] makes the rabbit a valuable model for studying viral entry and testing therapeutics. However, this also raises the theoretical risk that rabbits could serve as a reservoir or intermediate host for emerging coronaviruses. The finding that Omicron BA.4/5 variants of SARS-CoV-2 have significantly enhanced binding affinity to rabbit ACE2 [7] underscores the need for constant surveillance at the human-animal interface. While there is no evidence that RbCoV is zoonotic, the potential for recombination between RbCoV and other betacoronaviruses, as demonstrated for dromedary camel coronavirus HKU23 [9], is a genuine concern. Recombination events can alter host range and tissue tropism. Therefore, biosecurity measures designed to control RbCoV also serve a broader public health function by minimizing the circulation of coronaviruses in a species that is highly permissive to infection by multiple coronaviruses, including SARS-CoV-2 [7] and MERS-CoV [11]. The lack of MERS-CoV transmission in rabbits [11] is reassuring, but it does not preclude the possibility that a future variant could acquire the ability to transmit efficiently in this species.

Conclusion of Strategies

The prevention and control of rabbit coronavirus disease demands a sophisticated, integrated strategy that transcends simple vaccination or disinfection. It requires a deep understanding of the viral ecology within the rabbitry, the implementation of rigorous, multi-layered biosecurity protocols, the deployment of sensitive molecular diagnostics for early detection, and the development of effective immunoprophylactic tools. The multifactorial nature of the disease, as elucidated by Arnal et al. [1], dictates that control measures must be equally multifaceted, targeting the virus, the host, the environment, and the management practices that create the conditions for disease. The rabbit industry must move towards a culture of continuous surveillance and proactive management, rather than reactive crisis control. The tools and knowledge exist; the challenge lies in their consistent and disciplined application across the entire production chain.

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