Livestock Zoonoses: A Comprehensive Overview of Bacterial and Viral Diseases Transmitted from Farm Animals to Humans

Introduction

Zoonotic diseases originating from livestock represent a persistent challenge to veterinary public health and agricultural biosecurity. The close contact between humans and production animals, combined with intensive farming practices, facilitates the spillover of pathogens across species barriers. This article provides a systematic review of major bacterial and viral zoonoses transmitted from farm animals, with emphasis on transmission mechanisms, host-pathogen interactions, and diagnostic strategies. The discussion adheres strictly to veterinary and comparative biology perspectives, drawing on standard veterinary textbooks for bacterial agents and a curated set of peer-reviewed publications for viral pathogens [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14].

Bacterial Zoonoses from Livestock

Bacterial zoonoses remain a significant concern in livestock production systems. Pathogens such as Salmonella spp., Campylobacter spp., Leptospira spp., Brucella spp., and Mycobacterium bovis are well-documented causes of human disease following direct or indirect contact with infected animals or their products (Merck Veterinary Manual). Transmission occurs via fecal-oral routes, ingestion of contaminated milk or meat, inhalation of aerosols, or percutaneous inoculation. The clinical manifestations in livestock range from asymptomatic carriage to severe systemic illness, and accurate diagnosis relies on culture, serology, and molecular methods such as PCR.

Salmonella enterica serovars, particularly Typhimurium and Enteritidis, are frequently isolated from poultry, swine, and cattle. Colonization of the gastrointestinal tract leads to shedding in feces, contaminating the environment and food chain. Campylobacter jejuni is a leading cause of human gastroenteritis and is commonly carried by poultry flocks without clinical signs. Leptospira spp. infect cattle, swine, and sheep, with renal carriage resulting in urinary shedding; serovars such as Hardjo and Pomona are associated with reproductive losses in livestock and flu-like illness in humans. Brucella abortus and B. melitensis cause brucellosis in cattle and small ruminants, respectively, with transmission through contact with placental tissues, milk, or aerosols. Mycobacterium bovis is the causative agent of bovine tuberculosis, a chronic respiratory disease that can be transmitted to humans via inhalation or unpasteurized dairy products.

Diagnostic approaches for bacterial zoonoses include culture on selective media, biochemical identification, serological assays (e.g., ELISA, agglutination tests), and nucleic acid amplification techniques. Antimicrobial susceptibility testing is critical given the emergence of resistant strains. Control measures in livestock involve vaccination, biosecurity protocols, test-and-slaughter programs, and pasteurization of milk.

Viral Zoonoses from Livestock

Viral zoonoses transmitted from livestock encompass a diverse array of RNA and DNA viruses. The following sections detail key viral pathogens, with emphasis on recent molecular and serological findings from the provided literature.

Hepatitis E Virus (HEV)

Hepatitis E virus (HEV) is a single-stranded positive-sense RNA virus belonging to the family Hepeviridae. Genotypes 3 and 4 are zoonotic, with swine and wild boar serving as primary reservoirs [1, 4, 5, 11]. Transmission occurs via fecal-oral route, consumption of undercooked pork products, or direct contact with infected animals. HEV genotype 3 has been detected in wild boar populations in Argentina, indicating a potential reservoir for human infection [1]. In southern Italy, seroprevalence studies in pigs revealed exposure to HEV and other zoonotic pathogens, underscoring the need for surveillance [2]. Near full-length genome analysis of HEV genotype 4b in pigs from Guangdong, China, showed up to 99.944% nucleotide similarity to a human patient strain, confirming direct zoonotic transmission [5]. Additionally, HEV genotype 6 has been identified in Japanese wild boar, and an infectious cDNA clone was generated that replicated in human cell lines, demonstrating the virus's capacity for cross-species infection [7]. In Sierra Leone, domestic pigs were found to harbor HEV genotype 3 strains, with seroprevalence indicating widespread exposure [11]. Beyond swine, HEV has been detected in wild and domestic rabbits in Portugal, suggesting a broader host range [6]. Rat HEV (Rocahepevirus ratti) exposure has been documented in cats and dogs in Hong Kong, raising questions about potential spillover into companion animals [12].

Tick-Borne Encephalitis Virus (TBEV)

Tick-borne encephalitis virus (TBEV) is a flavivirus transmitted primarily by Ixodes ticks. Livestock such as cattle and goats can serve as sentinel hosts and, through infected milk, act as a source of alimentary infection for humans. In northwestern Iran, TBEV RNA was detected in raw milk samples, marking the first such report in that region [8]. In northeastern France, serological surveys in cattle revealed exposure to TBEV in historical endemic zones, confirming ongoing circulation [9]. These findings highlight the role of livestock in the epidemiology of TBEV and the importance of milk pasteurization as a preventive measure.

Severe Fever with Thrombocytopenia Syndrome Virus (SFTSV)

Severe fever with thrombocytopenia syndrome virus (SFTSV) is an emerging phlebovirus (family Phenuiviridae) transmitted by ticks and also through direct contact with infected animals. SFTSV has been reported in farm-raised fur animals in China, with direct transmission to workers documented [10]. Additionally, the first reported cases of SFTSV transmission from domestic sick camels to humans were described in China, expanding the known host range [13]. The virus causes hemorrhagic fever and thrombocytopenia in humans, and its control strategy involves tick management, surveillance, and public health education [14].

Borna Disease Virus (BDV)

Borna disease virus (BDV) is a negative-sense RNA virus that causes neurological disease in horses and sheep. Its zoonotic potential remains debated, but serological evidence of BDV antibodies has been found in alpacas in Bavaria, Germany, indicating exposure in South American camelids [3]. The presence of BDV in livestock warrants continued monitoring for potential cross-species transmission.

Diagnostic Approaches for Viral Zoonoses

Diagnosis of viral zoonoses in livestock relies on a combination of serological and molecular techniques. Enzyme-linked immunosorbent assays (ELISA) are widely used for detection of antibodies against HEV, TBEV, and SFTSV. Reverse transcription PCR (RT-PCR) and real-time RT-PCR provide sensitive and specific detection of viral RNA in blood, feces, milk, and tissue samples. Sequencing and phylogenetic analysis are essential for genotyping and tracing transmission chains [5, 7]. For HEV, near full-length genome sequencing has proven valuable in confirming zoonotic links [5]. For TBEV, RT-PCR on raw milk samples enables early detection of alimentary risk [8]. For SFTSV, molecular detection in animal tissues and human blood is critical for outbreak investigation [10, 13].

The following Mermaid diagram illustrates the general transmission pathways for livestock zoonoses, highlighting the interfaces between animal reservoirs, vectors, environment, and human exposure.

flowchart TD
 A[Livestock Reservoir] -->|Direct contact| B[Human Exposure]
 A -->|Fecal-oral| C[Contaminated Food/Water]
 A -->|Aerosol| D[Inhalation]
 A -->|Tick bite| E[Vector Transmission]
 E --> B
 C --> B
 D --> B
 A -->|Milk| F[Unpasteurized Dairy]
 F --> B
 B -->|Diagnosis| G[Serology/Molecular Testing]
 G --> H[Surveillance & Control]

One Health Implications

The interconnectedness of human, animal, and environmental health is exemplified by livestock zoonoses. Surveillance in wild boar populations is critical for understanding HEV ecology [1, 4]. The detection of HEV in rabbits and rats further complicates the epidemiological landscape [6, 12]. For TBEV, cattle serve as sentinels and potential sources of foodborne infection [8, 9]. SFTSV emergence in camels and fur animals underscores the need for expanded host surveillance [10, 13]. Integrated control strategies include vaccination of livestock where available, biosecurity measures, vector management, and public education on safe food handling.

Conclusion

Livestock zoonoses encompass a broad spectrum of bacterial and viral pathogens with significant implications for veterinary medicine and public health. Bacterial agents such as Salmonella, Campylobacter, Leptospira, and Brucella remain endemic in many production systems, while emerging viruses like HEV, TBEV, and SFTSV pose evolving threats. Molecular diagnostics and genomic surveillance are essential tools for detecting and characterizing these pathogens. A One Health approach, integrating veterinary, environmental, and human health sectors, is necessary to mitigate the risks of zoonotic transmission from farm animals.

References

[1] Williman MM, Colina SE, Di Cola G, et al. Evidence of Wild Boars as a Reservoir of Zoonotic Hepatitis E Virus Genotype 3: Implications for Public Health in Argentina. Pathogens. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/41754457/

[2] Ferrara G, Moje N, Rossi A, et al. Exposure to three zoonotic pathogens in the pig population of Southern Italy. Acta Trop. 2025. URL: https://pubmed.ncbi.nlm.nih.gov/40164402/

[3] Kirmayer LI, Lendl C, Wittek T. Occurrence of antibody titers against Borna disease virus in alpacas in Bavaria, Germany. Tierarztl Prax Ausg G Grosstiere Nutztiere. 2025. URL: https://pubmed.ncbi.nlm.nih.gov/39965579/

[4] Castagna F, Liguori G, Lombardi R, et al. Hepatitis E and Potential Public Health Implications from a One-Health Perspective: Special Focus on the European Wild Boar (Sus scrofa). Pathogens. 2024. URL: https://pubmed.ncbi.nlm.nih.gov/39452712/

[5] Deng H, Chen Y, Liang S, et al. Near full-length genome analysis of HEV 4b subtype in pigs showed a similarity up to 99.944% compared to a patient in Guangdong province, China. J Med Virol. 2024. URL: https://pubmed.ncbi.nlm.nih.gov/38949212/

[6] Santos-Silva S, Santos N, López-López P, et al. Hepatitis E virus in wild and domestic rabbits from Portugal: a combined molecular and longitudinal serological study. Vet Res Commun. 2024. URL: https://pubmed.ncbi.nlm.nih.gov/38935173/

[7] Primadharsini PP, Takahashi M, Nishizawa T, et al. The Full-Genome Analysis and Generation of an Infectious cDNA Clone of a Genotype 6 Hepatitis E Virus Variant Obtained from a Japanese Wild Boar: In Vitro Cultivation in Human Cell Lines. Viruses. 2024. URL: https://pubmed.ncbi.nlm.nih.gov/38932135/

[8] Parsadanians A, Mirshahabi H, Yavarmanesh M. First detection of tick-borne encephalitis virus (TBEV) in raw milk samples in North-Western Iran. Vet Med Sci. 2024. URL: https://pubmed.ncbi.nlm.nih.gov/38896036/

[9] Mathews-Martin L, Gonzalez G, Dheilly NM, et al. Exposure of cattle to tick-borne encephalitis virus in the historical endemic zone in north-eastern France. BMC Vet Res. 2024. URL: https://pubmed.ncbi.nlm.nih.gov/38796429/

[10] Li J, Wang C, Li X, et al. Direct transmission of severe fever with thrombocytopenia syndrome virus from farm-raised fur animals to workers in Weihai, China. Virol J. 2024. URL: https://pubmed.ncbi.nlm.nih.gov/38760812/

[11] Suluku R, Jabaty J, Fischer K, et al. Hepatitis E Seroprevalence and Detection of Genotype 3 Strains in Domestic Pigs from Sierra Leone Collected in 2016 and 2017. Viruses. 2024. URL: https://pubmed.ncbi.nlm.nih.gov/38675900/

[12] Shun EH, Situ J, Tsoi JY, et al. Rat hepatitis E virus (Rocahepevirus ratti) exposure in cats and dogs, Hong Kong. Emerg Microbes Infect. 2024. URL: https://pubmed.ncbi.nlm.nih.gov/38551320/

[13] Sun Y, Zhang D, Liu H, et al. The first reported cases of severe fever with thrombocytopenia syndrome virus from domestic sick camel to humans in China. Emerg Microbes Infect. 2024. URL: https://pubmed.ncbi.nlm.nih.gov/38269573/

[14] Casel MA, Park SJ, Choi YK. Severe fever with thrombocytopenia syndrome virus: emerging novel phlebovirus and their control strategy. Exp Mol Med. 2021. URL: https://pubmed.ncbi.nlm.nih.gov/33953322/ *** 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.