Equine Rotavirus A

Overview and Taxonomy of Equine Rotavirus A

Equine rotavirus A (ERVA) represents a significant etiological agent of neonatal foal diarrhea, imposing a substantial economic burden on the global equine breeding industry. As a member of the family Reoviridae, subfamily Sedoreovirinae, and genus Rotavirus, ERVA is classified within the species Rotavirus A, one of nine distinct rotavirus species (Rotavirus A through I, and the tentative Rotavirus J) recognized by the International Committee on Taxonomy of Viruses (ICTV). The taxonomic distinction is primarily based on the antigenic properties of the inner capsid protein VP6, which defines the group-specific antigen. Group A rotaviruses are the most clinically significant, infecting a broad range of mammalian and avian hosts, including humans, and are the leading cause of severe, dehydrating gastroenteritis in the young of numerous species. The World Organisation for Animal Health (WOAH) recognizes rotavirus infection as a critical cause of neonatal morbidity in foals, and the World Health Organization (WHO) lists rotavirus as a primary target for global vaccination programs in humans, underscoring the pathogen's cross-species relevance.

Genomic Architecture and Classification System

The ERVA virion is a non-enveloped, triple-layered icosahedral particle approximately 70–100 nm in diameter. Its genome consists of 11 segments of linear, double-stranded RNA (dsRNA), each encoding at least one protein. Six segments encode structural viral proteins (VP1–VP4, VP6, VP7), which form the three concentric protein layers: the core (VP1, VP2, VP3), the inner capsid (VP6), and the outer capsid (VP7 and the spike protein VP4). The remaining five to six segments encode non-structural proteins (NSP1–NSP5/6), which are essential for viral replication, morphogenesis, and pathogenesis, including the enterotoxin NSP4, which is a key driver of secretory diarrhea. The segmented nature of the genome is a fundamental driver of ERVA diversity, as it permits genetic reassortment during co-infection of a single cell with two or more distinct rotavirus strains. This mechanism allows for the rapid exchange of entire gene segments, generating novel progeny viruses with unique combinations of phenotypic traits, including altered host range, antigenicity, and virulence.

The standard classification system for rotaviruses, endorsed by the Rotavirus Classification Working Group (RCWG), employs a dual genotyping scheme based on the nucleotide sequences of the two outer capsid proteins: the glycoprotein VP7 (G-type) and the protease-sensitive protein VP4 (P-type). This binary GxP[x] nomenclature is the cornerstone of rotavirus epidemiology. For equine rotaviruses, the predominant genotypes circulating globally are G3P[1] and G14P[1] [2, 1, 3, 4]. The G3 genotype is further subdivided into lineages, with the G3A subtype being the most frequently identified in equine populations [2]. The P[1] genotype is considered the canonical equine P-type, and its VP4 gene exhibits a unique electrophoretic mobility in polyacrylamide gels that can vary depending on acrylamide concentration, a phenomenon not observed in other P genotypes [5]. While G3P[1] and G14P[1] are dominant, the full genotype constellation, which includes the VP6 (I-type), VP1 (R-type), VP2 (C-type), VP3 (M-type), NSP1 (A-type), NSP2 (N-type), NSP3 (T-type), NSP4 (E-type), and NSP5 (H-type) genes, reveals a more nuanced picture. Complete genome sequencing of reference strains such as FI-14 (G3P[1]) and FI23 (G14P[1]) has established that G3P[1] strains typically possess a VP6 genotype of I6, while G14P[1] strains carry an I2 VP6 genotype, a distinction that has implications for diagnostic test performance and viral evolution [1, 6].

Genetic Diversity and the Emergence of Unusual Constellations

The genetic landscape of ERVA is far more complex than the simple predominance of G3P[1] and G14P[1] suggests. Whole-genome sequencing has unveiled a remarkable diversity, including the detection of strains with constellations that challenge the traditional host-species boundaries. A landmark study from India identified two equine rotavirus isolates, ERV4 and ERV6, with a completely unique genotype constellation: G3-P[7]-I8-R3-C3-M3-A9-N3-T3-E3-H6 [8]. This constellation was not only unprecedented in equines but was identical to that of a bat rotavirus strain (MSLH14) from China. Furthermore, several of the individual gene segments (VP3, NSP2, NSP3) shared >95% nucleotide identity with bat RVA strains from Africa, while others (VP1, VP2, VP7, NSP1, NSP4) were closely related to human strains of bat origin [8]. The VP7 gene of these Indian isolates clustered into a new lineage (lineage X) of the G3 genotype, alongside bat, human, and alpaca strains, and the VP4 gene was a distinct P[7] lineage [8]. This finding provides compelling evidence for the inter-species transmission and reassortment of rotaviruses between bats and horses, highlighting the role of horses as potential mixing vessels for viruses from diverse ecological niches. The detection of such a bat-like ERVA underscores the "terra incognita" of rotavirus diversity and the critical need for comprehensive genomic surveillance under a One Health framework, as advocated by the WHO and the Food and Agriculture Organization (FAO) [8].

Further expanding the known diversity, equine rotavirus B (ERVB) has emerged as a significant pathogen in foals, particularly in central Kentucky, USA, since 2021 [9, 10]. While not a Group A virus, its emergence is contextually critical. ERVB strains possess a conserved genomic constellation (G3–P[7]–I3–R3–C3–M3–A4–N3–T3–E3–H3) and are genetically more closely related to ruminant rotavirus B strains than to other equine rotaviruses, suggesting a recent host-jump event from cattle or other ruminants [10]. The virus has demonstrated extreme environmental stability, being detected in soil, water, and even indoor barn equipment on affected farms, and has shown a high seroprevalence (87%) in surveyed horses [10]. The identification of a caprine rotavirus B strain with an identical genotype constellation and high nucleotide identity to ERVB further supports the hypothesis of a common source or ongoing inter-species transmission among livestock [11]. This highlights that the taxonomic and epidemiological picture of equine rotaviruses is not static and that novel pathogens can rapidly establish themselves in new hosts.

The Zoonotic Bridge: Equine-like G3 Strains in Humans

Perhaps the most profound revelation in recent rotavirus research is the global emergence and dissemination of "equine-like G3" strains in the human population. Since 2013, a novel reassortant virus, designated equine-like G3P[12], has been detected on five continents, causing significant outbreaks of acute gastroenteritis in children and adults [13, 14, 15, 16, 17]. These strains are not typical human G3 rotaviruses. Instead, they possess a VP7 gene that is phylogenetically distinct and most closely related to equine G3 rotaviruses, such as the Erv105 strain [18, 17, 19]. Critically, this equine-derived VP7 gene is carried on a DS-1-like genetic backbone (I2-R2-C2-M2-A2-N2-T2-E2-H2), which is typically associated with human G2P[20] strains [14, 16, 17, 21]. This makes them intergenogroup reassortants, combining genetic material from a zoonotic source (equine VP7) with a human-adapted backbone. The equine-like G3P[12] strains have become dominant in many regions, including Brazil, Belgium, Japan, Thailand, and Australia, often replacing previously circulating human G3P[12] strains [14, 15, 22, 23, 24]. In Australia, for example, equine-like G3P[12] accounted for 29.3% of all rotavirus-positive samples in 2023 [24]. The emergence of these strains has been temporally associated with the post-COVID-19 pandemic period, with a notable increase in cases among older children (2–5 years and 7–12 years), suggesting that reduced viral circulation during pandemic lockdowns led to waning population immunity [14, 22].

The public health implications are substantial. Studies have shown that the equine-like G3P[12] strain can cause severe disease, including nosocomial outbreaks in pediatric hospitals and community-wide outbreaks linked to contaminated water sources [25, 26]. Importantly, vaccine effectiveness (VE) studies have yielded mixed but concerning results. A study in Haiti found that two doses of the monovalent Rotarix vaccine were 64% effective against hospitalization due to equine-like G3P[12], which, while protective, was lower than the VE against other strains [27]. In Belgium, vaccinated individuals were significantly overrepresented among those infected with equine-like G3P[12] compared to other genotypes, suggesting that current vaccines may offer suboptimal protection against this emerging strain [14]. This is further supported by antigenic analyses showing that the VP7 protein of equine-like G3 strains possesses several amino acid substitutions in key neutralizing epitopes (e.g., 7-1a, 7-1b, 7-2) when compared to the G3 component of the RotaTeq vaccine [28, 29, 30, 16]. A sibling cluster in Malaysia demonstrated that a fully vaccinated child developed moderate disease from equine-like G3P[12] infection, while two unvaccinated siblings suffered severe, prolonged illness, illustrating that vaccination can attenuate disease but may not prevent breakthrough infection [30]. The ongoing evolution of these strains, including the detection of novel NSP2 lineages and further reassortment events (e.g., G3P[31] and G3P[20] variants), underscores the dynamic nature of this zoonotic threat and the imperative for continuous molecular surveillance as recommended by the WHO Global Rotavirus Surveillance Network [29, 32, 33, 19]. The emergence of equine-like G3 strains in humans serves as a powerful case study in the One Health paradigm, demonstrating how a pathogen circulating in an animal reservoir can acquire the genetic tools to cross the species barrier and pose a significant challenge to public health.

Molecular Pathogenesis of Equine Rotavirus A Infection

The molecular pathogenesis of Equine Rotavirus A (ERVA) infection represents a complex, multi-faceted process that begins with viral entry into the intestinal epithelium and culminates in profound disruption of enterocyte function, fluid homeostasis, and intestinal barrier integrity. Understanding these mechanisms at the molecular level is critical for developing effective countermeasures, particularly given the significant economic impact of ERVA on the global equine breeding industry and the emerging zoonotic potential of equine-derived rotavirus strains [2, 13, 1]. The World Organisation for Animal Health (WOAH) recognizes rotavirus as a major cause of neonatal diarrhea in foals, underscoring its importance as a pathogen of international concern.

Viral Attachment and Cellular Entry: The VP4-VP7 Axis

The initial steps of ERVA infection are governed by the outer capsid proteins VP4 and VP7, which together define the G (glycoprotein) and P (protease-sensitive) genotypes that are fundamental to viral tropism and pathogenesis [1, 4]. The VP4 spike protein, encoded by genome segment 4, is a critical determinant of host cell attachment and entry. For ERVA, the predominant P genotype circulating globally is P[1], though the emergence of P[7] strains of bat origin in equine populations has been documented in India, highlighting the dynamic nature of rotavirus evolution [8, 4, 34]. The VP8* domain of VP4, generated by trypsin cleavage, is responsible for binding to sialic acid-containing receptors on the surface of mature enterocytes lining the small intestinal villi [35]. This interaction is highly specific; neutralizing antibodies targeting VP8* have been shown to prevent ERVA infection in vitro, demonstrating the critical role of this domain in the infectious process [35].

Following receptor binding, VP5*, the other cleavage product of VP4, mediates membrane penetration and viral uncoating. The VP7 glycoprotein, which forms the smooth outer capsid layer, plays a dual role: it stabilizes the virion and is also a major target of neutralizing antibodies [1, 3]. The two dominant ERVA genotypes, G3P[1] and G14P[1], exhibit significant antigenic divergence in their VP7 proteins. Structural modeling has revealed that G3 and G14 VP7 proteins possess distinct antigenic epitopes, which explains the limited cross-neutralization observed between these genotypes [1]. This antigenic divergence has profound implications for vaccine efficacy, as the current commercially available inactivated vaccine is monovalent, containing only a G3P[1] strain [20, 1, 4]. The VP7 of G14P[1] strains possesses a non-conserved N-linked glycosylation site at position D123N, which may alter the antigenic surface and contribute to immune evasion [3].

Intracellular Replication and the Role of the Genomic Constellation

Once internalized, the double-stranded RNA (dsRNA) genome of ERVA, consisting of 11 segments, is transcribed within the cytoplasm by the viral RNA-dependent RNA polymerase (VP1) associated with the capping enzyme VP3 [13]. The segmented nature of the rotavirus genome is the molecular foundation for reassortment, a process whereby gene segments from different parental viruses can mix during co-infection, generating novel strains with altered pathogenic potential [13, 8]. This mechanism is central to the emergence of equine-like G3 strains that have caused widespread outbreaks in human populations [12, 14, 15, 28, 16].

The genotypic constellation of ERVA strains provides critical insights into their evolutionary history and pathogenic potential. Classic equine G3P[1] strains typically possess a VP6 genotype of I6, while G14P[1] strains carry I2 [1, 6]. This difference in VP6, the inner capsid protein that defines rotavirus group and subgroup specificity, may influence interactions with the host immune system. Whole-genome sequencing of ERVA isolates from India (ERV4 and ERV6) revealed a completely unique constellation: G3-P[7]-I8-R3-C3-M3-A9-N3-T3-E3-H6, which was identical to that of a bat rotavirus strain from China [8]. This finding demonstrates that ERVA can acquire entire genomic backbones from non-equine species, dramatically altering its molecular pathogenesis. The VP6 genotype I8, previously unreported in equines, suggests that these strains may have different replication kinetics or immune evasion capabilities compared to conventional equine strains [8].

Enterocyte Damage and Diarrheal Mechanisms

The hallmark of ERVA pathogenesis is the infection and subsequent destruction of mature enterocytes at the tips of small intestinal villi. Experimental infection of neonatal mice with equine G3P[1] and G14P[1] strains has provided a detailed temporal map of the pathological process. Viral replication peaks at approximately 48 hours post-infection (hpi), correlating with the maximum number of infected enterocytes detected by RNAscope in situ hybridization [36]. This peak in viral replication is accompanied by significant microscopic intestinal alterations, including enterocyte vacuolation, scalloping of the villous surface, and crypt hyperplasia [36]. These histological changes persist for at least 96 hpi, even as viral RNA levels decline to below detectable limits by 72–96 hpi, indicating that the structural damage to the intestinal epithelium outlasts active viral replication [36].

The functional consequences of enterocyte infection are profound. Using an organ culture model of equine jejunal explants, researchers demonstrated that ERVA infection, even in the absence of overt ultrastructural damage visible by electron microscopy, causes a significant decrease in the activity of microvillar membrane enzymes [37]. Specifically, analytical subcellular fractionation revealed a loss of the main brush border peak of modal density 1.21 g/ml, indicating that rotavirus impairs the turnover and function of microvillar membrane proteins [37]. This enzymatic dysfunction disrupts the digestive and absorptive capacity of the small intestine, leading to osmotic diarrhea. The non-structural protein NSP4, a viral enterotoxin, further exacerbates fluid loss by acting as a calcium-dependent secretagogue, triggering chloride secretion from crypt cells and disrupting the sodium-glucose cotransport system [13, 8].

Host Restriction and Species Barrier

The ability of ERVA to replicate in heterologous hosts is limited, a phenomenon known as host restriction. In the neonatal mouse model, equine G3P[1] and G14P[1] strains induced diarrhea at rates of 88% and 61%, respectively, but viral replication was short-lived, with viral loads declining rapidly after 48 hpi [36]. This contrasts with the more sustained replication observed with homologous porcine or bovine strains in the same model. The limited intestinal viral replication of equine strains in mice is likely associated with species-specific differences in cellular receptors, host restriction factors, and the innate immune response [36]. This host restriction is a critical barrier to interspecies transmission, but it is not absolute. The emergence of equine-like G3P[12] strains in humans, which have acquired a human P[12] VP4 gene while retaining the equine G3 VP7, demonstrates that reassortment can overcome this barrier [12, 14, 15, 28, 16].

The Molecular Basis of Zoonotic Potential

The most compelling evidence for the zoonotic potential of ERVA comes from the global emergence of equine-like G3P[12] strains. These are intergenogroup reassortants that possess an equine-derived G3 VP7 gene on a human DS-1-like genetic backbone (I2-R2-C2-M2-A2-N2-T2-E2-H2) [12, 14, 15, 28, 16, 17, 21]. Phylogenetic analyses indicate that the equine-like G3 VP7 lineage (lineage IX) is genetically distinct from typical human G3 strains and is most closely related to equine G3 strains such as Erv105 [28, 18, 16, 17]. The acquisition of the equine VP7 by a human rotavirus backbone likely occurred through a reassortment event in a host co-infected with both equine and human rotaviruses, possibly in Asia during the early 2010s [15, 17].

The molecular consequences of this reassortment are significant. The equine-like G3 VP7 protein carries specific amino acid substitutions in neutralizing epitopes compared to human G3 strains and vaccine strains (e.g., RotaTeq). In strains from Benin, substitutions at positions 156 (A156V), 260 (I260V), and 250 (K250E) were identified in the VP7 antigenic regions [29]. Similarly, VP4 of equine-like G3P[12] strains from Malaysia exhibited substitutions N195G, N195D, N113D, and D133N when compared to vaccine strains [29]. These changes may allow the virus to partially escape vaccine-induced immunity, which is supported by epidemiological data showing that vaccinated individuals were significantly overrepresented among patients infected with equine-like G3P[12] rotavirus compared to those infected with typical human G3P[12] strains in Belgium [14]. Despite this, vaccine effectiveness against equine-like G3P[12] remains moderate, with two doses of monovalent rotavirus vaccine in Haiti showing 64% effectiveness against hospitalization due to this genotype [27].

Environmental Stability and Transmission Dynamics

The molecular structure of ERVA contributes to its remarkable environmental stability, which is a key factor in its pathogenesis and transmission. As a non-enveloped virus, ERVA is resistant to many common disinfectants, including amphoteric soaps and quaternary ammonium compounds, which are frequently used in veterinary hygiene [4]. Alcohol-based products, aldehydes, and chlorine- and iodine-based compounds are required for effective inactivation [4]. This stability allows ERVA to persist in the farm environment for extended periods. In central Kentucky, ERVB (a related group B rotavirus) genome fragments were detected in 94% of soil samples and 100% of water samples from affected farms, as well as in 58% of indoor samples from equipment, barns, and hospital wards [10]. While these data are for ERVB, the non-enveloped nature of ERVA suggests similar environmental persistence, facilitating fecal-oral transmission and making biosecurity a critical component of disease control [4]. The detection of equine rotavirus genetic material in surface water used for drinking water production further underscores the potential for environmental contamination to drive outbreaks [38].

Hematological and Biochemical Correlates of Infection

The systemic effects of ERVA infection extend beyond the gastrointestinal tract. Hematological analysis of diarrheic foals reveals a pattern consistent with dehydration and acute phase response. Red blood cell counts, packed cell volume (PCV), and neutrophil counts increase progressively from the first to the sixth month of age in affected foals, reflecting hemoconcentration due to fluid loss [39]. Conversely, hemoglobin levels, lymphocyte counts, and monocyte counts decrease, indicating a shift towards innate immune activation and potential immunosuppression [39]. Serum biochemistry reveals significant electrolyte disturbances, with decreased sodium, potassium, and chloride levels, alongside elevated creatinine, bilirubin, and urea nitrogen, indicative of pre-renal azotemia secondary to dehydration [39]. Elevated liver enzymes (ALT, AST, GGT) and calcium levels suggest hepatic involvement or stress, while decreased glucose and alkaline phosphatase (ALP) reflect reduced intestinal absorptive capacity and enterocyte damage [39]. These molecular and biochemical alterations collectively contribute to the clinical syndrome of lethargy, anorexia, and diarrhea that characterizes ERVA infection in foals [2, 4].

Clinical Disease and Pathological Features in Foals and Animal Models

Equine rotavirus A (ERVA) infection manifests as a clinically significant, acute enteric disease primarily affecting neonatal foals, with the most severe consequences observed in individuals between one week and six months of age [4, 39]. The clinical syndrome is characterized by a rapid onset of profuse, watery to semi-liquid diarrhea, often accompanied by systemic signs including pyrexia, lethargy, and anorexia, the latter frequently presenting as a marked decrease in suckling behavior [4]. The pathophysiological cascade underlying these clinical signs is rooted in the virus’s tropism for mature enterocytes lining the small intestinal villi, leading to a characteristic malabsorptive and secretory diarrhea.

Clinical Manifestations in Foals

The hallmark of ERVA infection is acute diarrhea, which can range from mild, self-limiting episodes to severe, life-threatening dehydration and electrolyte imbalance. In a comprehensive epidemiological investigation of 36 outbreaks across Ireland during the 2023–2024 foaling season, the clinical presentation was consistently associated with debilitating diarrhea in neonatal foals, with affected animals often requiring intensive supportive care [2]. The severity of disease is influenced by several factors, including the infecting viral genotype, the level of maternally derived immunity, and the foal’s age at the time of infection. A sero-epidemiological survey in Japan demonstrated that G3P[1] strains were the predominant circulating type, with serological evidence of widespread infection in yearlings, underscoring the endemic nature of the virus and the frequent exposure of young horses [40].

Hematological and serum biochemical alterations in diarrheic foals provide critical insights into the systemic impact of ERVA infection. A study conducted in Khyber Pakhtunkhwa, Pakistan, documented significant deviations in hematological parameters, including elevated red blood cell counts, packed cell volume, and neutrophil numbers, which are indicative of hemoconcentration secondary to fluid loss [39]. Conversely, hemoglobin levels, lymphocyte counts, and monocyte numbers were observed to decrease, reflecting the acute stress response and potential immunosuppression [39]. Serum chemistry profiles in these foals revealed a complex metabolic disturbance: creatinine, bilirubin, albumin, blood urea nitrogen, and liver enzymes (ALT, AST, GGT) were elevated, suggesting prerenal azotemia and hepatic stress, while glucose, alkaline phosphatase, and critical electrolytes such as sodium, potassium, and chloride were decreased, consistent with severe diarrheal losses and metabolic acidosis [39]. These findings underscore the profound physiological derangement that can accompany ERVA infection, necessitating aggressive fluid and electrolyte therapy.

The duration of clinical signs is typically short-lived in uncomplicated cases, with diarrhea often resolving within 2–4 days. However, the economic impact on the equine breeding industry is substantial, driven by the costs of veterinary care, lost nursing time, and the potential for secondary complications such as aspiration pneumonia or septicemia in severely compromised neonates. The World Organisation for Animal Health (WOAH) recognizes rotavirus as a significant cause of neonatal diarrhea in foals, highlighting its importance to global equine health.

Pathological Features and Intestinal Lesions

The pathological hallmark of ERVA infection is the destruction of mature, absorptive enterocytes on the tips of the small intestinal villi, leading to villous atrophy, crypt hyperplasia, and a consequent reduction in the absorptive surface area. This structural damage is the direct cause of the malabsorptive diarrhea observed clinically. Detailed histopathological analyses in experimental models have elucidated the temporal progression of these lesions. In a seminal study using neonatal mice as a model for ERVA pathogenesis, infection with both G3P[1] and G14P[1] strains induced significant microscopic intestinal alterations [36]. These alterations were characterized by enterocyte vacuolation, scalloping of the villous epithelium, and crypt hyperplasia, with the peak of pathological change occurring at 48 hours post-infection (hpi) and persisting until at least 96 hpi [36]. Importantly, these histological changes correlated directly with the clinical presentation of diarrhea and the kinetics of viral replication, as demonstrated by RNAscope® in situ hybridization, which showed a gradual decline in the number of infected enterocytes from 72 to 96 hpi, coinciding with the resolution of diarrhea [36].

The specific genotype of ERVA may influence the severity and nature of the pathological lesions. Comparative studies have revealed that while both G3P[1] and G14P[1] strains cause similar clinical disease, there are notable differences in their replication kinetics and pathological impact. In the neonatal mouse model, G3P[1] infection resulted in a higher rate of diarrhea (88%) compared to G14P[1] (61%), suggesting a potential difference in virulence or host adaptation [36]. This differential pathogenicity may be linked to the distinct VP7 and VP6 genotypes of these strains; G3P[1] strains typically possess a VP6 of genotype I6, while G14P[1] strains carry VP6 genotype I2 [1, 6]. The VP6 protein is a major target of the host immune response and may influence the efficiency of viral replication and the extent of enterocyte damage.

Further insights into the cellular pathology of ERVA have been gained through organ culture studies of equine jejunal explants. These studies demonstrated that while rotavirus replication and assembly occurred within enterocytes, the brush borders and intracellular organelles often appeared ultrastructurally intact [37]. However, despite the absence of overt structural damage, analytical subcellular fractionation revealed a significant decrease in the activities of microvillar membrane enzymes, particularly a loss of the main brush border peak [37]. This finding indicates that ERVA can impair enterocyte function by disrupting the turnover of microvillar membrane proteins, leading to functional deficits in digestion and absorption even before widespread cell lysis occurs. This subcellular pathology helps explain the rapid onset of diarrhea and the profound electrolyte losses seen in affected foals.

Animal Models for Pathogenesis and Preclinical Research

The development of reliable animal models is critical for advancing the understanding of ERVA pathogenesis and for evaluating the efficacy of vaccines and therapeutics. The neonatal mouse has emerged as a particularly valuable model, as it recapitulates many of the key clinical and pathological features of ERVA infection in foals. Experimental oral inoculation of neonatal mice with equine, bovine, and porcine RVA strains consistently induces a short-lived diarrheal illness, with viral replication kinetics characterized by a gradual decline in viral load to undetectable levels by 72–96 hpi [36]. This pattern mirrors the self-limiting nature of the disease in foals and is directly correlated with the reduction in the number of infected enterocytes and the peak of intestinal histological alterations [36]. The mouse model has proven instrumental in demonstrating that the limited intestinal viral replication observed is likely due to host restriction factors, a phenomenon that is also relevant to understanding the species barriers that limit cross-species transmission [36].

The neonatal mouse model has also been used to compare the pathogenicity of different ERVA genotypes. As noted, G3P[1] and G14P[1] strains produce distinct rates of diarrhea and viral shedding, providing a platform for dissecting the molecular determinants of virulence [36]. Furthermore, this model is being explored as a preclinical tool for assessing vaccine efficacy, as it allows for the controlled evaluation of immune protection against homologous and heterologous challenge. The clinical and pathological phenotypes developed by neonatal mice following experimental infection are considered sufficiently robust to serve as a surrogate for the natural disease in foals, facilitating the rapid screening of candidate vaccines and therapeutic interventions [36].

Other in vitro models, such as the organ culture of equine small intestinal explants, have provided complementary insights into the cellular mechanisms of enterocyte damage [37]. While not a whole-animal model, this system allows for the direct observation of viral replication and its effects on brush border enzyme activity, offering a reductionist approach to studying the molecular pathology of ERVA. The successful isolation of ERVA strains, including G14P[1], in cell culture systems using engineered cell lines defective in antiviral innate immunity has further advanced the field, enabling the production of defined viral stocks for experimental infections and vaccine development [1, 3].

Comparative Pathology and Zoonotic Implications

The pathological features of ERVA infection in foals share fundamental similarities with rotavirus-induced gastroenteritis in other mammalian species, including humans. The destruction of villous enterocytes, subsequent villous atrophy, and crypt hyperplasia are conserved pathological responses across species. However, the emergence of equine-like G3P[12] strains in human populations has brought a new dimension to the study of ERVA pathology, as these reassortant viruses have been associated with significant disease in children. Since 2013, equine-like G3P[12] strains carrying a DS-1-like genetic backbone have been detected globally, causing outbreaks of severe acute gastroenteritis in pediatric populations [14, 15, 16, 17, 21]. In some regions, such as Brazil, these strains rapidly became dominant, replacing typical human G3P[12] strains [15, 21]. The clinical severity of these equine-like strains in children is comparable to that of other rotavirus genotypes, with cases often requiring hospitalization due to dehydration and electrolyte imbalance [17, 41]. A notable case in Italy involved an 8-year-old child with severe diarrhea, vomiting, and high fever, leading to pre-renal failure, highlighting the potential for these zoonotic strains to cause serious disease even in older children [41].

The pathological basis for the success of equine-like G3P[12] strains in humans is an area of active investigation. Whole-genome sequencing has revealed that these strains possess a unique constellation of genes, with the VP7 gene derived from an equine rotavirus and the remaining genes from a human DS-1-like backbone [16, 17, 21]. This reassortment event may have resulted in a virus that combines the antigenic novelty of the equine VP7 (allowing it to escape pre-existing immunity in humans) with the replication fitness of a human-adapted backbone. The Centers for Disease Control and Prevention (CDC) has recognized the importance of monitoring these emerging strains, as they may have implications for vaccine effectiveness. Indeed, studies have shown that current rotavirus vaccines, such as Rotarix and RotaTeq, may be less effective against equine-like G3P[12] strains compared to typical human strains, although they still provide significant protection against severe disease [14, 27]. The pathological and clinical data from both foals and human cases underscore the dynamic nature of rotavirus evolution and the critical need for continued surveillance and research into the mechanisms of cross-species transmission and pathogenesis.

Epidemiology and Risk Factors of Equine Rotavirus A Outbreaks

Equine rotavirus A (ERVA) represents one of the most significant infectious disease challenges to the global equine breeding industry, responsible for substantial morbidity, mortality, and economic losses attributable to neonatal foal diarrhea. Understanding the intricate epidemiological patterns and multifactorial risk determinants that govern ERVA outbreaks is paramount for the development of rational, evidence-based control strategies. The epidemiology of ERVA is a complex tapestry woven from viral genetic diversity, host immune dynamics, management practices, and increasingly, the recognition of interspecies transmission events that have implications extending into human public health.

Global Distribution and Prevalent Genotypes

The global epidemiological landscape of ERVA is dominated by two principal genotypes, G3P[1] and G14P[1], which together account for the vast majority of outbreaks in foals worldwide [2, 1, 3, 4, 40]. However, the relative prevalence of these genotypes is neither static nor geographically uniform. Longitudinal surveillance in major Thoroughbred breeding regions reveals dynamic shifts in the dominant circulating strains. For instance, in central Kentucky, a seminal serotyping study had historically reported only G3 genotype strains; however, molecular characterization of samples from the 2017 foaling season demonstrated a marked shift, with the G14P[1] genotype emerging as the predominant strain for the first time in that region [3]. This pattern is mirrored by data from Ireland, where analysis of 377 samples submitted from 36 outbreaks during 2023–2024 identified 37 G3 strains across 26 premises and 7 G14 strains across 6 premises, confirming the co-circulation of both genotypes within a single outbreak season [2]. Critically, the genomic architecture of these strains often reveals a consistent distinction: G3P[1] strains typically possess a VP6 genotype I6, whereas G14P[1] strains carry a VP6 genotype I2, a molecular marker that facilitates epidemiological tracking and suggests divergent evolutionary histories [1, 6]. The implications of this genotypic divergence are profound, particularly regarding vaccine efficacy, as the current commercially available inactivated vaccine is monovalent, containing only a G3P[1] strain [20, 4]. This mismatch between vaccine composition and circulating field strains has been posited as a direct risk factor for breakthrough outbreaks, a hypothesis supported by data from studies demonstrating limited cross-neutralization between these two genotypes in vitro [1]. Indeed, the G14P[1] genotype has been responsible for increased diarrhoea outbreaks in foals born to dams immunized with the monovalent G3P[1] vaccine, underscoring a critical vulnerability in current prevention strategies [1].

Farm-Level Risk Factors and Management Practices

Epidemiological investigations have illuminated critical modifiable risk factors that operate at the farm level. Data from the recent Irish outbreak investigation provide a nuanced view of the interplay between vaccination coverage, hygiene standards, and stocking density [2]. In that study, attending veterinary surgeons assessed farm hygiene standards and stocking rates as “satisfactory” on the majority of affected premises, yet a striking 68% of dams of affected foals were unvaccinated [2]. This finding powerfully identifies inadequate maternal vaccination coverage as the single most impactful, modifiable risk factor for ERVA outbreaks, even on farms with otherwise acceptable biosecurity practices. The failure to vaccinate pregnant mares creates a cohort of foals that enter the world without adequate maternally derived neutralizing antibodies (NAbs), rendering them highly susceptible to infection. The biological basis for this is well-established: vaccination of pregnant mares significantly increases serum NAb titers, which are then passively transferred to the foal exclusively via colostrum, as pre-nursing serum samples from foals contain no detectable NAbs [20]. The protective window afforded by this passive immunity is finite, with serum NAb titers in foals declining steadily over time, reaching their nadir at approximately four months of age [20]. Critically, data from experimental and field studies demonstrate that vaccination of mares can confer protection, albeit with variable efficacy, and that foals born to vaccinated mares which do become infected tend to exhibit milder clinical signs compared to those born to unvaccinated dams [42, 43]. Therefore, the risk of an outbreak is not merely a function of viral presence but is fundamentally determined by the collective susceptibility of the foal population, a state directly governed by herd-level immunity passively transferred from vaccinated mares.

Beyond immunity, the epidemiological role of the farm environment as a viral reservoir and transmission vehicle cannot be overstated. ERVA is a non-enveloped virus, exhibiting exceptional environmental stability and resistance to many common disinfectants, including amphoteric soaps and quaternary ammonium compounds, which are frequently used in veterinary hygiene protocols but are generally ineffective against the virus [4]. This environmental persistence transforms affected premises into long-term risk zones. A comprehensive investigation of equine rotavirus B (ERVB) in Kentucky, a related but distinct group B rotavirus, provides a powerful analogy for ERVA transmission dynamics, demonstrating that viral genomes were detected in 94.12% of soil samples and 100% of water samples from positive farm premises, as well as in 58.33% of indoor samples from barn equipment and hospital wards [10]. This indicates that once introduced, rotaviruses can contaminate the entire farm ecosystem, creating a sustained source of infection for successive foal crops. Stocking density, while assessed as satisfactory in the Irish study, remains a biologically plausible risk factor, as higher densities increase the frequency of foal-to-foal contact, fecal-oral transmission opportunities, and the environmental viral load, thereby accelerating outbreak propagation [2].

Foal Age and Maternal Immunity Dynamics

The age of the foal is a critical intrinsic risk factor, governed by the intersection of waning maternal immunity and the timing of exposure. Diarrhea in equine neonates due to ERVA is typically observed within the first few months of life, with peak susceptibility often coinciding with the decline of passive colostral antibodies [20]. The dynamics of maternally derived immunity involve a complex interplay. While colostral NAbs are highly protective, they can also interfere with the active immunization of foals if vaccination is attempted while titers are still high, a phenomenon documented in studies showing that maternal NAb titers at 30 and 45 days of age are often too high for effective vaccination [31]. This creates a window of vulnerability: as maternal titers wane below a protective threshold, the foal becomes susceptible, but early vaccination may be ineffective due to antibody interference. However, recent innovative protocols have shown that vaccination at two and three months of age, or even at three months alone, can stabilize or increase NAb titers against both G3 and G14 viruses, offering a potential strategy to close this immunological gap [31]. The risk is therefore not uniform across all foals but is concentrated in those whose dams possess either low vaccine-boosted titers or whose colostral transfer was suboptimal. The variation in the ratio of NAbs transferred from the serum of mares to the serum of their foals is a recognized phenomenon that further individualizes risk, as some foals may receive a lower functional dose of protective antibody even from a vaccinated dam [20].

Zoonotic Spillover and One Health Implications: The Equine-Like G3P[12] Paradigm

Perhaps the most paradigm-shifting aspect of ERVA epidemiology is the recognition of its profound zoonotic potential, which has reshaped our understanding of the virus from a purely veterinary concern to a One Health priority. Starting in 2013, an unprecedented global emergence of an “equine-like” G3P[12] rotavirus strain in human pediatric populations was documented, causing severe gastroenteritis and hospitalizations in children across multiple continents [13, 15, 28, 16]. This strain is a reassortant possessing an equine-origin VP7 gene (G3) but inserted into a human DS-1-like genotype backbone (I2-R2-C2-M2-A2-N2-T2-E2-H2) [14, 17, 21, 44, 45]. The epidemiological risk factors associated with this zoonotic emergence are not those of direct foal-to-human transmission on farms but are instead driven by global viral evolution, reassortment, and human population dynamics. The equine-like G3P[12] strain was first detected in Asia in the early 2010s and rapidly disseminated globally, with phylogeographic analyses tracing its spread from Asia to Europe, the Caribbean, and South America [15]. In Brazil, it became the dominant strain between 2017 and 2020, completely replacing the human Wa-like G3P[12] strains in some regions [15, 21]. Similarly, in Thailand, the prevalence of this equine-like G3P[12] genotype increased explosively from 5.5% in 2014 to 89.8% in 2016 [23].

The risk factors for human infection with this equine-derived strain are fundamentally different from those in horses and are linked to human demographic and epidemiological shifts. The COVID-19 pandemic had a profound impact on rotavirus epidemiology, leading to reduced circulation during lockdowns, followed by a massive resurgence [14, 22]. In Belgium and Japan, post-pandemic resurgence was characterized by an unusual and extreme dominance of equine-like G3P[12] strains, accompanied by a marked shift in the age distribution of cases, with older children aged 2–5 years and 7–12 years becoming significantly overrepresented [14, 22]. This is attributed to waning immunity in older children who were not exposed to the virus during pandemic lockdowns, creating a larger pool of susceptible individuals [22]. Furthermore, data indicate that vaccinated individuals are overrepresented among those infected with equine-like G3P[12] compared to other genotypes, suggesting that current human rotavirus vaccines may be less effective against this zoonotic reassortant [14]. These findings underscore a critical risk factor: the emergence of equine-like strains is placing selective pressure on vaccine efficacy in human populations, a phenomenon reported by the World Health Organization (WHO) as a key area for ongoing surveillance. The detection of equine rotavirus sequences in surface water used for drinking water production further highlights a potential environmental transmission pathway for these zoonotic strains [38].

The genomic plasticity of rotaviruses, driven by their segmented RNA genome, is the fundamental biological mechanism underpinning these epidemiological shifts. Reassortment events between equine and human rotaviruses are not infrequent and have generated novel strains such as the human G3P[20] strain in Japan, whose VP7 gene showed high identity to an equine rotavirus [33]. Even more alarmingly, whole-genome sequencing of ERVA isolates from India revealed an unusual genomic constellation (G3-P[7]-I8-R3-C3-M3-A9-N3-T3-E3-H6) that was previously reported only in a bat rotavirus strain, indicating a complex and previously unrecognized cross-species transmission cycle involving bats, horses, and potentially humans [8]. This finding, highlighting the terra incognita of equine rotavirus diversity, suggests that equids can serve as mixing vessels for rotaviruses from diverse mammalian hosts, including wildlife, thus acting as a potential source of novel, pandemic-capable strains [8, 18]. The detection of ERVA VP7 genes in human strains from Thailand that also share ancestry with bat rotaviruses further reinforces this model, illustrating that the equine lineage is a major donor of genetic material in the global rotavirus ecosystem [18].

Vaccination Status and Antigenic Mismatch as a Risk Factor

The status of the dam’s vaccination is the most critical, directly controllable risk factor for ERVA outbreaks in foals. As established, the current inactivated G3P[1] vaccine is safe and immunogenic, capable of raising serum NAb titers in mares, which are then transferred to foals via colostrum [42, 43]. However, the monovalent nature of this vaccine constitutes a significant risk in regions where G14P[1] strains are prevalent or dominant. Serological and neutralization studies have confirmed that while vaccination with G3P[1] does generate some cross-reactive NAbs against G14P[1], the heterologous titers are 2- to 4-fold lower [20, 1]. This quantitative reduction in cross-protection may be sufficient to allow breakthrough infections in foals, particularly under high challenge pressure or when colostral antibody transfer is suboptimal. The field efficacy of the G3 vaccine against heterologous G14 challenge has been described as “limited and controversial,” a conclusion supported by the observation of G14 outbreaks on farms with vaccinated mares [3, 42]. The absence of a G14 antigen in the vaccine represents a critical deficiency in current outbreak prevention strategies. Furthermore, the widespread lack of vaccination uptake, exemplified by the 68% of unvaccinated dams in affected Irish outbreaks, represents a massive missed opportunity for prevention, transforming susceptible foal populations into reservoirs for viral amplification and transmission [2].

The role of diagnostic sensitivity as a risk factor for uncontrolled outbreaks must also be considered. The rapid antigen detection (RAD) kits commonly used in field practice offer high concordance with RT-PCR but exhibit a diagnostic ceiling, failing to detect virus at higher dilutions [7, 46]. This limitation means that weak positive or early-stage infections may be missed, leading to a failure to isolate infected foals promptly and effectively. False negative results are therefore a risk factor for continued within-farm transmission. Reliance on RADs without confirmatory RT-PCR for suspect cases creates a dangerous blind spot in outbreak detection and response [7]. The performance of these kits can also vary by genotype, as demonstrated when one commercial ELISA failed to detect the G3P[1]I6 genotype, highlighting the need for species- and genotype-specific assay validation [46].

In summary, the epidemiology of Equine Rotavirus A is characterized by a dynamic interplay between viral genotype flux, host immunity derived from maternal vaccination, and farm management practices. The emergence of G14P[1] as a globally significant genotype and the zoonotic spillover of equine-like G3P[12] into human populations have fundamentally altered the risk landscape. The World Organisation for Animal Health (WOAH) recognizes rotavirus as a significant equine pathogen, and the data collectively underscore that the most effective risk mitigation strategies must prioritize a high level of vaccination coverage in pregnant mares using a vaccine that adequately reflects the circulating G-type(s), while simultaneously recognizing the broader, interconnected nature of rotavirus ecology that spans animal and human health.

Diagnostic Approaches for Equine Rotavirus A Detection and Genotyping

The accurate and timely detection of equine rotavirus A (ERVA) is paramount not only for the clinical management of neonatal foal diarrhea but also for informing epidemiological surveillance, guiding vaccination strategies, and understanding the zoonotic potential of emerging strains. The diagnostic landscape for ERVA has evolved significantly, moving from classical virological methods to a sophisticated arsenal of rapid antigen detection (RAD) tests, molecular amplification techniques, and high-resolution genomic sequencing platforms. The selection of a diagnostic approach is dictated by the clinical context, the need for rapid turnaround time for isolation and treatment decisions, the requirement for high sensitivity in research or outbreak investigations, and the necessity for comprehensive genotyping to track viral evolution and cross-species transmission events. This section provides a deep analysis of the biological principles, performance characteristics, and strategic applications of each diagnostic modality for ERVA.

Clinical Detection of ERVA: From Rapid Antigen Tests to Molecular Assays

The first line of diagnosis in field settings or clinical veterinary practice typically relies on the detection of viral antigen in fecal samples. Commercially available rapid antigen detection (RAD) kits, often based on immunochromatographic principles originally designed for human rotavirus, have been evaluated for their suitability in equine diagnostics. A comprehensive study comparing two RAD kits against a reference real-time RT-PCR assay demonstrated that these kits can be highly useful for on-site screening, with both evaluated kits showing a high level of concordance (>95%) with PCR [7]. However, a critical biological limitation of these assays is their analytical sensitivity; testing of serial dilutions of RT-PCR-positive feces revealed that the RADs consistently failed to detect the virus at higher dilutions, indicating a higher limit of detection compared to nucleic acid amplification tests [7]. This suggests that while a positive RAD result in a diarrheic foal is highly indicative of ERVA infection, a negative result, particularly from a suspect case with weak clinical signs, cannot rule out infection and should be confirmed by a more sensitive laboratory-based method [7, 47]. The utility of these tests in clinical practice is further supported by evidence that they are simple to perform, require minimal equipment, and can facilitate immediate decisions regarding the isolation of affected foals and the initiation of supportive care [4].

Beyond immunochromatographic strips, enzyme-linked immunosorbent assays (ELISAs) have been a mainstay of rotavirus diagnosis. An in-depth comparative study of two commercial kits (Pathfinder™ Rotavirus and FASTest Rota® strip) and an in-house KERI ELISA revealed profound differences in their ability to detect ERVA, particularly concerning genetic diversity within the VP6 gene [46]. The FASTest Rota® strip demonstrated superior sensitivity (92%) and specificity (97%) for equine RVA detection, while the Pathfinder™ assay showed markedly lower sensitivity (32%). Critically, the study identified that the Pathfinder™ kit, which employs a monoclonal antibody, failed specifically to detect the G3P[1]I6 genotype, a common equine genotype [46]. This finding underscores a fundamental biological principle: the sensitivity of antigen detection methods is intrinsically linked to the antigenic conservation of the target protein (typically VP6). The I6 VP6 genotype, characteristic of many equine G3P[1] strains, possesses a distinct molecular marker (a PP/Q residue at positions 299-300) that differentiates it from the I2 genotype found in equine G14P[1] strains [6]. Therefore, any diagnostic test, whether ELISA or immunochromatographic, must be validated against the specific VP6 genotypes circulating in the target equine population to avoid false-negative results due to antibody-epitope mismatches [46].

Molecular Detection and Quantification: The Role of RT-PCR and Real-Time RT-qPCR

For definitive diagnosis, confirmation of weak positives, and quantitative viral load assessment, reverse transcription polymerase chain reaction (RT-PCR) and its real-time quantitative variant (RT-qPCR) have become the gold standard. These assays target conserved regions of the viral genome, most often the VP7 or VP6 genes, to achieve high sensitivity and specificity. The standard approach in many diagnostic laboratories involves a real-time RT-PCR assay that can detect ERVA nucleic acid even in samples with low viral titers [2, 7]. The sensitivity of these assays is exceptional; for instance, the detection limit for an RT-LAMP assay designed for ERVA was reported at 10³ copies of viral RNA, while semi-nested RT-PCR was less sensitive at 10⁵ copies [34]. However, standard RT-qPCR assays far exceed this, with one equine-like G3-specific TaqMan assay achieving a linear dynamic range from 2.3 x 10² to 2.3 x 10⁹ copies per reaction and a limit of detection of 227 copies [48].

The development of a specific TaqMan-based real-time RT-PCR assay for the equine-like G3 strain is a prime example of diagnostic adaptation to viral evolution [48]. This assay, which uses a universal G forward primer with a specific reverse primer and probe, allows for the simultaneous detection and quantification of the emerging equine-like G3P[12] DS-1-like reassortant strains in human populations, with 100% positive agreement and 99.63% negative agreement in validation studies [48]. In equine diagnostics, real-time RT-PCR is routinely used for surveillance and outbreak investigations. A study of ERVA outbreaks in Ireland used this method to confirm infection in 48 foals from 36 outbreaks, highlighting the technique's reliability for detecting the predominant G3 and G14 genotypes [2]. The ability to quantify viral RNA is not merely academic; it has implications for understanding pathogenesis. Experimental infections in neonatal mice demonstrated a gradual decline in viral load in feces, corresponding with a reduction in infected enterocytes, a pattern that was closely monitored using RT-qPCR [36]. This quantitative data allows researchers to correlate viral replication kinetics with clinical signs and histopathological changes.

An alternative molecular technique, reverse transcription loop-mediated isothermal amplification (RT-LAMP), offers a bridge between the simplicity of RADs and the sensitivity of PCR. An RT-LAMP assay designed to target the P[1] genotype (the predominant VP4 type in equine rotaviruses) demonstrated superior sensitivity compared to semi-nested RT-PCR, detecting the virus in 58 of 96 samples versus 25 by PCR [34]. Its key advantage is its isothermal nature, eliminating the need for a thermal cycler, and the results can be visualized without gel electrophoresis, making it highly applicable for field-based or resource-limited diagnostic laboratories [34]. However, its specificity is genotype-dependent, targeting P[1] specifically, which could be a limitation if novel or reassortant strains with different P genotypes emerge.

Genotyping of ERVA: From Binary G/P Typing to Whole-Genome Characterization

While detection is critical for individual animal management, genotyping is essential for epidemiological surveillance, understanding viral evolution, and assessing vaccine efficacy. The binary classification system based on the VP7 (G-type) and VP4 (P-type) outer capsid proteins is the standard initial approach. Genotyping is typically achieved by amplifying the complete VP7 and VP4 genes via RT-PCR followed by Sanger sequencing. Phylogenetic analysis of these sequences allows for the assignment of specific lineages and the differentiation of strains from different geographical regions and time periods. For example, in Ireland, sequencing of VP7 and VP4 genes from 2023-2024 outbreaks classified all detected viruses as G3A subtype and P[1] genotype, closely related to European and Japanese strains [2]. Similarly, the co-circulation of G3P[1] and G14P[1] strains in central Kentucky was confirmed through molecular characterization of fecal samples [3]. This binary typing is crucial for identifying the most prevalent genotypes and detecting shifts, such as the increasing dominance of G14P[1] in some regions, which has implications for vaccine composition, given that current vaccines are monovalent G3P[1] formulations [1, 4, 42].

However, the dynamic nature of rotavirus evolution, driven by point mutations, genetic drift, and importantly, reassortment of the segmented genome, necessitates a more comprehensive approach. Whole-genome sequencing (WGS) and complete genome constellation analysis, as recommended by the Rotavirus Classification Working Group (RCWG), have become indispensable for fully characterizing circulating strains and tracing their origins [13, 8]. WGS has unveiled unusual and potentially zoonotic constellations. For instance, the complete genome analysis of two ERVA isolates from India (ERV4 and ERV6) revealed a unique constellation (G3-P[7]-I8-R3-C3-M3-A9-N3-T3-E3-H6) that was identical to a bat rotavirus strain from China [8]. This finding, which included a VP6 of genotype I8 never before reported in equines, suggests a recent cross-species transmission event from bats, highlighting the power of WGS in uncovering "hidden" diversity and zoonotic pathways [8, 18]. Similarly, the widespread global emergence of the equine-like G3P[12] strain in humans was only fully understood through WGS, which confirmed a DS-1-like genetic backbone (I2-R2-C2-M2-A2-N2-T2-E2-H2) with an equine-origin VP7, a reassortment event that likely occurred in Asia in the early 2010s [13, 12, 15, 16, 17, 21, 44, 45].

The use of WGS also allows for the detailed analysis of antigenic epitopes, which is critical for vaccine design. For equine RVA, the two dominant genotypes, G3P[1] and G14P[1], share the same overall genomic constellation except for the VP7 and VP6 segments [1, 6]. Structural modeling of VP7 from these two genotypes has identified key amino acid substitutions in neutralizing epitopes (e.g., a non-conserved N-linked glycosylation site D123N in G14 strains) that explain the limited cross-neutralization observed in vitro [1, 3]. This genetic basis of antigenic divergence provides a molecular rationale for the failure of the monovalent G3P[1] vaccine to fully protect against heterologous G14P[1] challenge, supporting the urgent need for a bivalent vaccine [1, 4, 42].

Furthermore, amplicon-based next-generation sequencing (NGS) of specific genes (VP7, VP4, VP6) from environmental samples, such as surface water used for drinking, has enabled the tracking of RVA diversity across host species. This approach has successfully identified sequences from human, porcine, bovine, equine, and even feline rotaviruses in water sources, underscoring the role of environmental surveillance in monitoring the One Health dimension of rotavirus transmission [38]. The integration of these advanced genomic tools into routine surveillance programs, as recommended by organizations such as the World Organisation for Animal Health (WOAH) and the World Health Organization (WHO), is essential for detecting emerging strains like the equine-like G3 and for evaluating the long-term effectiveness of vaccination programs in both horses and humans [13, 14, 29, 22, 21]. The diagnostic and genotyping pipeline, therefore, must be a tiered system, where rapid, low-cost screening tests are complemented by high-sensitivity molecular confirmation and, ultimately, by whole-genome sequencing to provide the deep genomic insights necessary to combat this genetically agile pathogen.

Vaccination Strategies and Control Measures for Equine Rotavirus A

Equine Rotavirus A (ERVA) represents one of the most economically and clinically consequential infectious disease challenges confronting the global equine breeding industry. The pathogenesis of ERVA, characterized by acute, debilitating diarrhea in neonatal foals, is compounded by the virus’s remarkable environmental stability, its capacity for genetic reassortment, and the demonstrable limitations of current vaccination paradigms [2, 1, 3]. The development and implementation of effective vaccination strategies, coupled with rigorous biosecurity control measures, therefore constitute the cornerstone of ERVA management in endemic regions, particularly in high-density breeding operations such as those found in central Kentucky, Ireland, Japan, and Argentina [2, 3, 49]. This section provides an exhaustive analysis of the current state of ERVA vaccination, the immunological underpinnings of maternal antibody transfer, the critical issue of genotype mismatch between vaccines and circulating field strains, and the comprehensive control measures required to mitigate both clinical disease and viral spread.

The Monovalent G3P[1] Vaccine: Mechanisms, Immunogenicity, and Limitations

The cornerstone of ERVA prophylaxis for the past two decades has been the administration of inactivated, adjuvanted vaccines to pregnant mares, with the objective of boosting colostral immunoglobulin levels and thereby conferring passive immunity to the neonatal foal via the ingestion of colostrum [42, 43]. The vast majority of commercially available ERVA vaccines are formulated with a single G3 serotype, typically the G3P[1] genotype, reflecting the historical predominance of this genotype in global equine populations [4, 40]. Early field studies, including the pivotal randomized controlled trial by Powell et al. (1997), demonstrated that a three-dose regimen administered to mares at 8, 9, and 10 months of gestation was safe and immunogenic, producing a significant elevation in serum neutralizing antibody (NAb) titers in vaccinated mares compared to placebo controls [43]. These titers were effectively transferred to foals, persisting for up to 90 days post-partum, and were associated with a reduction in the incidence of rotaviral diarrhea, although the difference did not reach statistical significance in that initial study [43]. Subsequent work by Imagawa et al. (2005) corroborated these findings, showing that a two-dose vaccine regimen could induce NAb titers of 1:320 to 1:10,240 in foals, and while it did not prevent infection by a heterologous G14 strain, it significantly ameliorated the clinical severity of diarrhea [42].

The immunological mechanism underpinning this protection is the passive transfer of NAbs targeting the outer capsid proteins VP7 (the G-type determinant) and VP4 (the P-type determinant). Recent, highly detailed work by Eertink et al. (2024) has meticulously characterized the dynamics of this maternal antibody transfer in the context of current vaccination practices [20]. This study confirmed that pre-nursing foal serum contains no detectable NAbs against ERVA, establishing unequivocally that protection is entirely dependent on colostral ingestion [20]. Following nursing, foals acquire significant NAb levels, but the efficiency of transfer, the ratio of NAb titers in the foal’s serum to that of the mare, exhibits considerable inter-individual variation [20]. Critically, the study demonstrated that homologous NAbs (against G3P[1]) decline steadily, reaching their lowest point at approximately four months of age, leaving foals vulnerable to infection well before they reach six months of age, a period when ERVA remains a significant threat [20, 39]. This waning immunity creates a window of susceptibility that current vaccination schedules, which focus solely on the mare, cannot fully address.

The Challenge of Genotype Mismatch: G14P[1] Emergence and Antigenic Divergence

The most significant challenge to the efficacy of the monovalent G3P[1] vaccine is the global emergence and increasing prevalence of the G14P[1] genotype. While G3P[1] strains have historically been dominant, molecular epidemiological surveillance has consistently demonstrated the co-circulation of G14P[1] strains, which in some regions, such as central Kentucky, have even become the predominant cause of foal diarrhea [3, 40]. This genotypic shift has profound implications for vaccine efficacy. Carossino et al. (2018) were among the first to sound the alarm, reporting the successful isolation of G14P[1] strains from Kentucky and highlighting that the VP7 protein of these strains possesses critical amino acid substitutions in antigenic epitopes, including a non-conserved N-linked glycosylation site (D123N), which could alter the antigenic landscape recognized by vaccine-induced antibodies [3].

The molecular basis for the limited cross-protection between G3 and G14 strains has been rigorously dissected by Uprety et al. (2024) [1]. Using a novel cell culture system, they isolated contemporary G3P[1] and G14P[1] field strains and performed comprehensive cross-neutralization assays. The results were stark: the two genotypes demonstrated profoundly limited cross-neutralization. Serum raised against G3P[1] showed significantly reduced neutralizing capacity against G14P[1] [1]. This in vitro finding directly mirrors field observations, where outbreaks of G14P[1] diarrhea have occurred on farms with high vaccination coverage using the monovalent G3 vaccine [2, 1]. Structural modeling by Uprety et al. further elucidated the genetic basis for this antigenic divergence, demonstrating that the VP7 and VP4 proteins of the two genotypes occupy distinct antigenic clusters [1]. This has led to a consensus, articulated by Nemoto and Matsumura (2021) and supported by the World Organisation for Animal Health (WOAH), that the current G3-only vaccines are suboptimal and that the addition of a G14P[1] strain is a critical unmet need for the equine industry [4].

Furthermore, the conundrum is not limited to G3 versus G14. The emergence of equine Rotavirus B (ERVB) since 2021 in major breeding regions like Kentucky represents an entirely new challenge, as current ERVA vaccines provide no cross-protection against this distinct viral group [10]. The extreme environmental stability of ERVB, which can be detected in soil, water, and barn equipment months after an outbreak, underscores the necessity for a broader vaccine strategy that may eventually need to incorporate ERVB antigens [10, 11].

Foal Vaccination: Overcoming Maternal Antibody Interference

A major conceptual advancement in ERVA vaccination strategy has been the exploration of direct immunization of foals. Historically, this approach was considered futile due to the phenomenon of maternal antibody interference, where high titers of passively acquired NAbs neutralize the vaccine antigen, preventing the foal’s immune system from mounting a primary response. The work of Eertink et al. (2026) has directly challenged this dogma [31]. In a highly controlled study using foals from unvaccinated dams (to pre-determine low starting NAb titers), they demonstrated that immunization with the commercial G3P[1] vaccine at two and three months of age could not only stabilize but significantly increase NAb titers against both homologous G3 and heterologous G14 viruses [31]. Foals with pre-vaccination titers of ≤256 showed robust responses, with titers rising up to 1024 against G3 and 512 against G14 [31]. This contrasts sharply with unvaccinated foals, where titers declined rapidly over the same period. This study provides a proof-of-concept that foal-side vaccination may be a viable strategy, particularly for high-risk foals or those born to dams with suboptimal vaccination histories. The key variable is the pre-vaccination titer; foals with very high maternal antibody levels (titers >256) may still fail to respond, indicating that timing of foal vaccination must be carefully calibrated to the individual foal’s serological status, a practice that could be facilitated by the development of rapid, on-farm antibody titer tests.

Control Measures: Biosecurity, Diagnosis, and Environmental Management

Vaccination alone cannot prevent ERVA infection; a holistic control program requires rigorous biosecurity and environmental management. The diagnosis of ERVA is the first critical step in implementing control measures. Rapid antigen detection (RAD) kits, which are based on immunochromatographic principles, have become indispensable tools for field veterinarians due to their ease of use and rapid turnaround time [7, 4, 47]. Cullinane et al. (2025) conducted a comprehensive evaluation of two commercial RAD kits, demonstrating >95% concordance with laboratory-based real-time RT-PCR, making them excellent screening tools for identifying infected foals and initiating immediate isolation protocols [7]. However, the same study identified a critical limitation: RAD kits exhibit poor sensitivity at high dilutions (i.e., low viral loads). Therefore, the authors strongly recommend that any negative sample from a clinically suspect case, or any weak positive, be confirmed by a more sensitive molecular method such as real-time RT-PCR [7]. The work of Miño et al. (2015) further underscores that the performance of some RAD kits can vary based on the VP6 genotype of the circulating ERVA strain, with the Pathfinder™ assay showing poor sensitivity for G3P[1]I6 strains [46]. For more sophisticated molecular diagnostics, real-time RT-PCR remains the gold standard for quantification, and specific assays, such as the one developed by Katz et al. (2021) for equine-like G3 strains, are critical for surveillance [48]. Additionally, reverse transcription loop-mediated isothermal amplification (RT-LAMP) offers a highly sensitive and rapid alternative that does not require a thermocycler, making it suitable for well-equipped field laboratories [34].

Once a positive case is identified, immediate isolation of the affected foal and its dam is paramount. ERVA is a non-enveloped virus, conferring upon it exceptional resistance to many common disinfectants [4]. Alcohol-based hand sanitizers and amphoteric soaps are generally ineffective. Effective disinfection requires the use of aldehyde-based disinfectants (e.g., formalin, glutaraldehyde), chlorine-based compounds (e.g., sodium hypochlorite at 0.5-1% for hard, non-porous surfaces), or iodine-based compounds [4]. Quaternary ammonium compounds have variable and often insufficient activity against rotavirus and should be used with caution. Peracetic acid and accelerated hydrogen peroxide products are also highly effective.

Beyond immediate disinfection, the farm environment itself serves as a major reservoir. Sreenivasan et al. (2024) demonstrated that ERVB (and by extension, ERVA) genome fragments can be detected in soil samples from paddocks, water sources, and indoor barn equipment for extended periods [10]. This necessitates a comprehensive environmental management strategy. Contaminated bedding should be removed and composted carefully. Pasture rotation is not highly effective given environmental persistence, but reducing stocking density and the number of foals per paddock is critical [2]. The study by Cullinane et al. (2025) in Ireland emphasized that while hygiene standards on affected farms were often considered satisfactory, high stocking density remained a significant risk factor [2]. The use of separate footwear and coveralls for personnel entering foaling and isolation areas, coupled with footbaths containing an effective disinfectant (e.g., chlorine or peroxide-based), is a non-negotiable control measure. Furthermore, the One Health implications of ERVA cannot be ignored. The global emergence of the equine-like G3P[12] (eG3) strain in human pediatric populations, which carries a VP7 gene of clear equine origin on a human DS-1-like backbone, has demonstrated the zoonotic potential of equine rotaviruses [13, 14, 15, 16, 50]. This strain has been associated with vaccine breakthrough in children vaccinated with Rotarix and RotaTeq [30, 27]. Consequently, stringent biosecurity on equine premises is not only a horse health issue but a public health one, aligning with WOAH and WHO frameworks for emerging zoonotic pathogens. The control of ERVA must therefore be viewed through a One Health lens, integrating animal health surveillance, environmental hygiene, and human public health monitoring to preempt the next reassortment event and safeguard both animal and human populations [13, 8].

References

[1] Uprety T, Soni S, Sreenivasan CC, Hause B, Naveed A, Ni S, et al.. Genetic and antigenic characterization of two diarrhoeicdominant rotavirus A genotypes G3P[12] and G14P[12] circulating in the global equine population. Journal of General Virology. 2024. DOI: https://doi.org/10.1099/jgv.0.002016

[2] Cullinane A, Garvey M, Dayot L, Lukaseviciute G. Equine Rotavirus A Outbreaks in Ireland (2023–2024): An Epidemiological Investigation and Virus Genotyping. Viruses. 2025. DOI: https://doi.org/10.3390/v17040511

[3] Carossino M, Barrandeguy M, Li Y, Parreño V, Janes J, Loynachan A, et al.. Detection, molecular characterization and phylogenetic analysis of G3P[12] and G14P[12] equine rotavirus strains co-circulating in central Kentucky.. Virus Research. 2018. DOI: https://doi.org/10.1016/j.virusres.2018.05.025

[4] Nemoto M, Matsumura T. Equine rotavirus infection. Journal of Equine Science. 2021. DOI: https://doi.org/10.1294/jes.32.1

[5] Long-Croal LM, Wen X, Ostlund E, Hoshino Y. Concentration of acrylamide in a polyacrylamide gel affects VP4 gene coding assignment of group A equine rotavirus strains with P[12] specificity. Virology Journal. 2010. DOI: https://doi.org/10.1186/1743-422X-7-136

[6] Ma Y, Wen X, Hoshino Y, Yuan L. Cloning and Nucleotide Sequence Analyses of 11 Genome Segments of Two American and One British Equine Rotavirus Strains. Veterinary Microbiology. 2015. DOI: https://doi.org/10.1016/j.vetmic.2015.01.008

[7] Cullinane A, Nelly M, Dayot L, Lukaseviciute G, Garvey M, Healy J, et al.. Diagnostic Performance of Rapid Antigen Tests to Detect Equine Rotavirus A. Viruses. 2025. DOI: https://doi.org/10.3390/v17030413

[8] Pathak A, Gulati B, Maan S, Mor S, Kumar D, Soman R, et al.. Complete Genome Sequencing Reveals Unusual Equine Rotavirus A of Bat Origin from India. Journal of Virology. 2022. DOI: https://doi.org/10.1128/jvi.01408-22

[9] Gamage C, Graves AJ, Li G, Thieulent CJ, Balasuriya UBR, Morrow JK, et al.. Coding-complete genome sequences of group B equine rotavirus from central Kentucky, USA, reveal circulation of a single genome constellation. Microbiology Resource Announcements. 2025. DOI: https://doi.org/10.1128/mra.00744-25

[10] Sreenivasan CC, Naveed A, Uprety T, Soni S, Jacob O, Adam E, et al.. Epidemiological investigation of equine rotavirus B outbreaks in horses in central Kentucky.. Veterinary Microbiology. 2024. DOI: https://doi.org/10.1016/j.vetmic.2024.110278

[11] Paul L, Morgan J, Pulley G, Uprety T, Hause B, Ádám E, et al.. Genetic and phylogenetic relationship of an American caprine rotavirus B strain with equine rotavirus B. Frontiers in Virology. 2023. DOI: https://doi.org/10.3389/fviro.2023.1181017

[12] Hosseini-Fakhr S, Jalilvand S, Maleki A, Kachooei A, Behnezhad F, Mir-Hosseinian M, et al.. Genetic characterization of rotavirus A strains circulating in children under 5 years of age with acute gastroenteritis in Tehran, Iran, in 2023–2024: dissemination of the emerging equine-like G3P[8]-I2-E2 DS-1-like strains. Journal of General Virology. 2025. DOI: https://doi.org/10.1099/jgv.0.002088

[13] Carossino M, Vissani MA, Barrandeguy M, Balasuriya UBR, Parreño V. Equine Rotavirus A under the One Health Lens: Potential Impacts on Public Health. Viruses. 2024. DOI: https://doi.org/10.3390/v16010130

[14] Karataş M, Bloemen M, Cuypers L, Wollants E, Ranst MV, Matthijnssens J. 14 years of rotavirus A surveillance: unusual dominance of equine-like G3P[8] genotype with DS-1-like genotype constellation after the pandemic, Belgium, 2009 to 2023. Euro surveillance : bulletin Europeen sur les maladies transmissibles = European communicable disease bulletin. 2025. DOI: https://doi.org/10.2807/1560-7917.ES.2025.30.12.2400442

[15] Gutierrez MB, Arantes I, Bello G, Berto LH, Dutra LH, Kato RB, et al.. Emergence and dissemination of equine-like G3P[8] rotavirus A in Brazil between 2015 and 2021. Microbiology spectrum. 2024. DOI: https://doi.org/10.1128/spectrum.03709-23

[16] Bonura F, Bányai K, Mangiaracina L, Bonura C, Martella V, Giammanco G, et al.. Emergence in 2017-2019 of novel reassortant equine-like G3 rotavirus strains in Palermo, Sicily.. Transboundary and Emerging Diseases. 2021. DOI: https://doi.org/10.1111/tbed.14054

[17] Akane Y, Tsugawa T, Fujii Y, Honjo S, Kondo K, Nakata S, et al.. Molecular and clinical characterization of the equine-like G3 rotavirus that caused the first outbreak in Japan, 2016.. Journal of General Virology. 2021. DOI: https://doi.org/10.1099/jgv.0.001548

[18] Tacharoenmuang R, Guntapong R, Upachai S, Singchai P, Phatsaman T, Sutthiwarakom K, et al.. A novel bat-like human G3P[10] rotavirus strain from Thailand shares its VP7 lineage with equine Erv105 and human DS-1-like G3P[8] strains: a possible origin in bats.. Virology. 2026. DOI: https://doi.org/10.1016/j.virol.2026.110795

[19] Utsumi T, Wahyuni RM, Doan YH, Dinana Z, Soegijanto S, Fujii Y, et al.. Equine-like G3 rotavirus strains as predominant strains among children in Indonesia in 2015-2016.. Infection, Genetics and Evolution. 2018. DOI: https://doi.org/10.1016/j.meegid.2018.03.027

[20] Eertink LG, Swope M, Uprety T, Sreenivasan CC, Page AE, Adam E, et al.. Characteristics of maternal antibodies transferred to foals raised through maternal equine rotavirus A vaccination.. Veterinary Microbiology. 2024. DOI: https://doi.org/10.1016/j.vetmic.2024.110304

[21] Luchs A, Costa ACd, Cilli A, Komninakis S, Carmona R, Boen L, et al.. Spread of the emerging equine-like G3P[8] DS-1-like genetic backbone rotavirus strain in Brazil and identification of potential genetic variants.. Journal of General Virology. 2019. DOI: https://doi.org/10.1099/jgv.0.001171

[22] Fukuda Y, Fujii Y, Togashi A, Nawa T, Nakamura S, Kimura R, et al.. Recent Increase in Rotavirus Gastroenteritis After Five Years of Low Activity in Hokkaido Prefecture, Japan, Associated With Equine‐Like G3P[8] and G8P[8] Strains, 2025. Journal of Medical Virology. 2026. DOI: https://doi.org/10.1002/jmv.70967

[23] Tacharoenmuang R, Komoto S, Guntapong R, Upachai S, Singchai P, Ide T, et al.. High prevalence of equine‐like G3P[8] rotavirus in children and adults with acute gastroenteritis in Thailand. Journal of Medical Virology. 2020. DOI: https://doi.org/10.1002/jmv.25591

[24] Thomas S, Bogdanovic-Sakran N, Donato CM, Sriraman AT, Pavlic D, Bines JE. Australian Rotavirus Surveillance Program Annual Report, 2023.. Communicable diseases intelligence. 2025. DOI: https://doi.org/10.33321/cdi.2025.49.027

[25] Burlandy F, Casarin BC, Gutierrez MB, Cantelli CP, Novo SPC, Assis RMSd, et al.. Rotavirus Outbreak Traced in Clinical, Environmental, and Food Matrices: Whole Genomic Characterization of an Equine-like G3P[8] Genotype. Food and Environmnetal Virology. 2026. DOI: https://doi.org/10.1007/s12560-026-09678-2

[26] Gutierrez MB, Figueiredo MRd, Fialho A, Cantelli CP, Miagostovich M, Fumian T. Nosocomial acute gastroenteritis outbreak caused by an equine-like G3P[8] DS-1-like rotavirus and GII.4 Sydney[P16] norovirus at a pediatric hospital in Rio de Janeiro, Brazil, 2019. Human Vaccines & Immunotherapeutics. 2021. DOI: https://doi.org/10.1080/21645515.2021.1963169

[27] Burnett E, Juin S, Esona M, Desormeaux A, Aliabadi N, Pierre M, et al.. EFFECTIVENESS OF MONOVALENT ROTAVIRUS VACCINE AGAINST HOSPITALIZATIONS DUE TO ALL ROTAVIRUS AND EQUINE-LIKE G3P[8] GENOTYPES IN HAITI 2014–2019. Vaccine. 2021. DOI: https://doi.org/10.1016/j.vaccine.2021.06.055

[28] Vizzi E, Rosales RE, Piñeros O, Fernández R, Inaty D, López K, et al.. Emergence of Equine-like G3P[8] Rotavirus Strains Infecting Children in Venezuela. Viruses. 2025. DOI: https://doi.org/10.3390/v17030410

[29] Agbla JM, Mogotsi M, Zohoun AG, Shange ND, Capochichi A, Ogunbayo A, et al.. Unveiling a Shift in the Rotavirus Strains in Benin: Emergence of Reassortment Intergenogroup and Equine-like G3P[8] Strains in the Post-Vaccination Era. Viruses. 2025. DOI: https://doi.org/10.3390/v17081091

[30] Tahar AS, Ong EJ, Mamora D, Tan CS. Rotavirus Vaccine Breakthrough With Vaccine‐Modified Disease in a Sibling Cluster of Equine‐Like G3P[8] Infection. Journal of Medical Virology. 2026. DOI: https://doi.org/10.1002/jmv.70910

[31] Eertink LG, Jacob O, Adam E, Page AE, Wang D, Li F. Immunization of Foals with Equine Rotavirus A Vaccine Can Stabilize or Increase Rotavirus-Specific Neutralizing Antibody Titers. Viruses. 2026. DOI: https://doi.org/10.3390/v18050556

[32] Serra ACS, Júnior EC, Cruz JF, Lobo PS, Júnior ET, Bandeira RS, et al.. Molecular analysis of G3P[6] rotavirus in the Amazon region of Brazil: evidence of reassortment with equine-like strains.. Future Microbiology. 2021. DOI: https://doi.org/10.2217/fmb-2020-0002

[33] Malasao R, Saito M, Suzuki A, Imagawa T, Nukiwa-Soma N, Tohma K, et al.. Human G3P[4] rotavirus obtained in Japan, 2013, possibly emerged through a human–equine rotavirus reassortment event. Virus genes. 2014. DOI: https://doi.org/10.1007/s11262-014-1135-z

[34] Nemoto M, Imagawa H, Tsujimura K, Yamanaka T, Kondo T, Matsumura T. Detection of equine rotavirus by reverse transcription loop-mediated isothermal amplification (RT-LAMP).. Journal of Veterinary Medical Science. 2010. DOI: https://doi.org/10.1292/JVMS.09-0446

[35] Skrobarczyk JW, Flores-Ahlschwede P, Metcalfe L, Cohen ND, Berghman LR. Identification of 3 neutralizing linear epitopes on the VP8 outer capsid protein of group A equine rotavirus.. American Journal of Veterinary Research. 2023. DOI: https://doi.org/10.2460/ajvr.23.08.0193

[36] Gamage C, Holl W, Parreño V, Thieulent CJ, Balasuriya UBR, Vissani MA, et al.. Comparative clinical, virological and pathological characterization of equine rotavirus A G3P[12] and G14P[12] infection in neonatal mice. Journal of General Virology. 2025. DOI: https://doi.org/10.1099/jgv.0.002110

[37] Batt RM, Embaye H, Waal SVD, Burgess D, Edwards G, Hart C. Application of Organ Culture of Small Intestine to the Investigation of Enterocyte Damage by Equine Rotavirus. Journal of Pediatric Gastroenterology and Nutrition - JPGN. 1995. DOI: https://doi.org/10.1097/00005176-199504000-00011

[38] Miura T, Kadoya S, Takino H, Sano D, Akiba M. Temporal variations of human and animal Rotavirus A genotypes in surface water used for drinking water production. Frontiers in Microbiology. 2022. DOI: https://doi.org/10.3389/fmicb.2022.912147

[39] Durrani A, Husnain M, Haq I, Batool U, Khan F. First Report of Equine Rotavirus Infection in Khyber Pakhtunkhwa. International Bhurban Conference on Applied Sciences and Technology. 2019. DOI: https://doi.org/10.1109/IBCAST.2019.8667229

[40] Imagawa H, Tsunemitsu H, Wada R, Fukunaga Y. Sero-Epidemiological Survey of Equine Rotavirus Infections in 1-year-old Thoroughbred Horses in the Hidaka Region of Hokkaido. Journal of Equine Science. 2002. DOI: https://doi.org/10.1294/JES.13.71

[41] Esposito S, Camilloni B, Bianchini S, Ianiro G, Polinori I, Farinelli E, et al.. First detection of a reassortant G3P[8] rotavirus A strain in Italy: a case report in an 8-year-old child. Virology Journal. 2019. DOI: https://doi.org/10.1186/s12985-019-1173-1

[42] Imagawa H, Kato T, Tsunemitsu H, Tanaka H, Sato S, Higuchi T. Field Study of Inactivated Equine Rotavirus Vaccine. Journal of Equine Science. 2005. DOI: https://doi.org/10.1294/JES.16.35

[43] Powell D, Dwyer R, Traub-Dargatz J, Fulker R, Whalen JW, Srinivasappa J, et al.. Field study of the safety, immunogenicity, and efficacy of an inactivated equine rotavirus vaccine.. Journal of the American Veterinary Medical Association. 1997. DOI: https://doi.org/10.2460/javma.1997.211.02.193

[44] Martínez-Gutiérrez M, Hernández-Mira E, Rendon-Marin S, Ruíz-Sáenz J. Wa-1 Equine-Like G3P[8] Rotavirus from a Child with Diarrhea in Colombia. Viruses. 2021. DOI: https://doi.org/10.3390/v13061075

[45] Perkins C, Mijatovic-Rustempasic S, Ward M, Cortese M, Bowen M. Genomic Characterization of the First Equine-Like G3P[8] Rotavirus Strain Detected in the United States. Genome Announcements. 2017. DOI: https://doi.org/10.1128/genomeA.01341-17

[46] Miño S, Kern A, Barrandeguy M, Parreño V. Comparison of two commercial kits and an in-house ELISA for the detection of equine rotavirus in foal feces.. Journal of Virological Methods. 2015. DOI: https://doi.org/10.1016/j.jviromet.2015.05.002

[47] Nemoto M, Hata H, Higuchi T, Imagawa H, Yamanaka T, Niwa H, et al.. Evaluation of rapid antigen detection kits for diagnosis of equine rotavirus infection.. Journal of Veterinary Medical Science. 2010. DOI: https://doi.org/10.1292/JVMS.10-0064

[48] Katz EM, Esona M, Gautam R, Bowen M. Development of a Real-Time Reverse Transcription-PCR Assay To Detect and Quantify Group A Rotavirus Equine-Like G3 Strains. Journal of Clinical Microbiology. 2021. DOI: https://doi.org/10.1128/JCM.02602-20

[49] Parreño V, Miño S, Garaicoechea L, Barrandeguy M. Equine rotavirus in Argentinean foals: an overview. Journal of Equine Veterinary Science. 2016. DOI: https://doi.org/10.1016/J.JEVS.2016.02.052

[50] Amit LN, Mori D, John J, Chin AZ, Mosiun AK, Jeffree MS, et al.. Emergence of equine-like G3 strains as the dominant rotavirus among children under five with diarrhea in Sabah, Malaysia during 2018–2019. PLoS ONE. 2021. DOI: https://doi.org/10.1371/journal.pone.0254784

Disclaimer: This article is for educational and informational purposes only. It is not intended to substitute for professional veterinary advice, diagnosis, treatment, or regulatory guidance. Always consult a licensed veterinarian or qualified specialist regarding animal health, disease diagnosis, and therapeutic decisions.