Veterinary virology studies the viruses that affect domestic animals, livestock and wildlife, and their connection to public health. This article provides an integrated view: from the structural nature of viruses to clinical implications, diagnosis, and control strategies essential for veterinary professionals. (MacLachlan & Dubovi, 2021)
What is veterinary virology?
Veterinary virology is the discipline that studies viral agents and their relationship with animal hosts: their biology, transmission routes, pathogenic mechanisms, and measures for diagnosis and control. It integrates molecular biology, immunology, epidemiology and preventive medicine to address real sanitary problems. (Fenner, 2021)
Its importance is twofold: it protects animal production and pet welfare, and safeguards public health by controlling zoonotic viruses capable of spreading between animals and humans. Therefore, virological surveillance and timely response impact both clinical practice and health policy. (OIE, 2023)
1. Nature and fundamental characteristics of viruses
Viruses are acellular entities composed of genetic material (DNA or RNA) enclosed in a protein capsid; some also possess a lipid envelope. Lacking the machinery for independent replication, they invade host cells to utilize their replicative resources. (Robbins & Cotran, 2020)
These characteristics—genome type, presence of envelope, and capsid architecture—determine environmental stability, transmission capacity, and optimal diagnostic and disinfection strategies. For example, RNA viruses typically mutate faster than many DNA viruses, favoring variant emergence. (MacLachlan & Dubovi, 2021)
2. Types of viruses according to structure
Classifying viruses by structure is practical and clinically relevant: it determines environmental resistance, disinfectant susceptibility and transmission efficiency. Below are the main categories and representative veterinary examples. (Fenner, 2021)
- Characteristics: external lipid membrane derived from the host containing viral glycoproteins.
- Implications: higher sensitivity to detergents, heat and desiccation; often transmitted through close contact or droplets.
- Examples: Influenza A (birds/pigs), Bovine herpesvirus (IBR), Porcine coronavirus (PEDv). (Swayne, 2020; MacLachlan & Dubovi, 2021)
- Characteristics: lack an envelope; resistant protein capsid.
- Implications: greater environmental stability; resistant to common disinfectants and extreme pH, complicating sanitation in farms and clinics.
- Examples: Canine parvovirus, Canine adenovirus, Porcine circovirus. (Greene, 2018)
- Icosahedral: geometric symmetry that facilitates assembly (e.g., Adenoviridae, Parvoviridae).
- Helical: helical structure common in viruses with long, filamentous genomes (e.g., some respiratory viruses and arboviruses).
- Complex: poxviruses and others with additional layers and structural components. (Fenner, 2021)
3. Etiology and factors favoring viral infections
Viral etiology includes not only the infectious agent, but also host and environmental factors that facilitate disease. Age, immune status, population density, management and hygiene conditions influence infection likelihood and clinical severity. (Greene, 2018)
- High density and stress: intensive systems enhance transmission.
- Animal movement: trade and transport without sanitary control.
- Poor biosecurity: fomites, footwear, vehicles and personnel without control.
- Reservoirs and vectors: wildlife or arthropods that maintain the virus.
- Viral variability: mutations and recombinations that evade prior immunity.
Identifying and correcting these factors is the basis of effective prevention. (OIE, 2023)
4. Pathogenesis: from infection to lesion
Viral pathogenesis is the sequence of events linking exposure to the agent with clinical manifestations. After entry (respiratory, digestive, cutaneous or vector-borne), the virus binds to specific receptors, enters the cell, replicates and disseminates. Lesions may result from direct viral damage or host immune response. (MacLachlan & Dubovi, 2021)
Clinical progression depends on viral tropism (target tissues), infectious dose and prior immunity. For example, respiratory viruses damage epithelium and predispose to bacterial coinfections, whereas neurotropic viruses produce severe encephalopathies. (Greene, 2018)
- Cytolysis and loss of tissue function: viral replication destroying cells.
- Immunopathology: damage caused by exaggerated immune response.
- Persistence and latency: later reactivation (e.g., herpesviruses).
- Barrier disruption and coinfections: predisposition to secondary bacteria and fungi.
Understanding these mechanisms guides clinical management and prevention. (MacLachlan & Dubovi, 2021)
5. Morphological changes and pathological findings
Viruses produce characteristic microscopic and gross findings useful in diagnosis. Histological signs include intracellular inclusions, focal or diffuse necrosis, nonsuppurative inflammation and lymphoid tissue atrophy depending on the agent. (Zachary, 2017)
At necropsy, lesion distribution provides clues about entry route and tropism. Correlating these findings with molecular and serological tests enables a definitive diagnosis. (Robbins & Cotran, 2020)
- Nuclear/cytoplasmic inclusions: point toward specific viral families.
- Nonsuppurative encephalitis: suggests neurotropic agents (rabies, herpes, some arboviruses).
- Digestive epithelial necrosis: seen in parvoviruses and enteric coronaviruses.
6. Virological diagnosis: integration of methods
Accurate diagnosis integrates clinical signs, pathology and laboratory techniques. The most used tools are PCR/RT-PCR for genomic detection, ELISA for antigens or antibodies, immunohistochemistry to localize virus in tissue and viral isolation in culture when feasible. (OIE, 2023)
The choice of method depends on the infection phase (acute or convalescent), available sample, and the goal (confirmation, surveillance or molecular typing). Sequencing provides data on variants and outbreak origin. (MacLachlan & Dubovi, 2021)
- PCR/RT-PCR: rapid and specific diagnosis in acute phase.
- ELISA/serology: useful in prevalence studies and vaccine response.
- Immunohistochemistry: valuable in fixed tissues to confirm viral presence.
- Viral isolation: necessary for pathogenicity and vaccine studies, although slower.
Combining tests increases diagnostic certainty and guides control measures. (OIE, 2023)
7. Prevention, control and vaccination
Control of viral diseases is multifactorial: biosecurity policies, early diagnosis, isolation, sanitary management and vaccination programs are complementary pillars. Vaccination reduces morbidity and mortality and, in production systems, maintains profitability. (Zimmerman et al., 2019)
Biosecurity measures (access control, cleaning and disinfection, quarantines) are essential, especially for viruses stable in the environment such as parvoviruses. Active surveillance allows detection of antigenic changes that may require vaccine updates. (OIE, 2023)
- Scheduled vaccination and boosters according to species and regional guidelines. (Zimmerman et al., 2019)
- Strict quarantine protocols for incoming animals. (OIE, 2023)
- Vector and wildlife reservoir control. (Swayne, 2020)
- Disinfection with products effective for enveloped and non-enveloped viruses. (MacLachlan & Dubovi, 2021)
- Single-stranded RNA: high mutation rate (e.g., Orthomyxoviridae, partially Coronaviridae), important in variant emergence. (MacLachlan & Dubovi, 2021)
- Double-stranded DNA: greater genetic stability (e.g., Herpesviridae), associated with latency and reactivation. (Robbins & Cotran, 2020)
- Segmented: allows genetic reassortment, as in influenza A, with important epidemiological consequences. (Swayne, 2020)
The combination of structure and genome type defines epidemiological behavior and control strategies. (Fenner, 2021)
8. Clinical and epidemiological relevance
Clinical implications of viruses range from self-limiting infections to severe systemic disease. Epidemiologically, transmission efficiency and environmental persistence determine outbreak risk and required interventions. (OIE, 2023)
In livestock, viral outbreaks affect productivity, reproduction and trade; in companion animals, they impact mortality and quality of life. Zoonotic viruses also threaten human health, requiring collaboration between veterinarians and health authorities. (MacLachlan & Dubovi, 2021)
9. Conclusion
Veterinary virology combines basic and applied knowledge: understanding viral structure, infection cycle and immune response enables effective preventive measures. Combined use of molecular diagnosis, sanitary control and vaccines is the strongest strategy to reduce the impact of viral diseases in animals and humans. (Zimmerman et al., 2019)
Continuous surveillance, vaccine updates against emerging variants and improved biosecurity practices are priorities to face current and future threats. (OIE, 2023; MacLachlan & Dubovi, 2021)
Maintain a sampling and laboratory submission protocol, record vaccinations and control animal movement: simple actions that reduce risks and accelerate outbreak response.
References
• MacLachlan, N. J., & Dubovi, E. J. (2021). Fenner’s Veterinary Virology. Elsevier.
• Greene, C. E. (2018). Infectious Diseases of the Dog and Cat. Elsevier.
• OIE – World Organisation for Animal Health. Diagnostic Manual (2023).
• Fenner, A. (2021). Principles of Veterinary Virology. Elsevier.
• Robbins, S. L., & Cotran, R. S. (2020). Robbins Basic Pathology. Elsevier.
• Swayne, D. E. (2020). Avian Influenza. Wiley.
• Zimmerman, J. et al. (2019). Disease of Swine. Wiley.