Challenges in navigating molecular diagnostics for common equine respiratory viruses.
Authors: Pusterla Nicola, Leutenegger Christian M, Barnum Samantha, Wademan Cara, Hodzic Emir
Journal: Veterinary journal (London, England : 1997)
Summary
# Editorial Summary Equine respiratory viruses continue to threaten herd health globally, compounded by ageing horse populations, increased international trade, and expanding pathogen distribution. Pusterla and colleagues reviewed the current landscape of molecular diagnostics—particularly PCR-based testing—for common equine respiratory infections, highlighting both the considerable advantages these rapid, sensitive techniques offer over traditional microbiology and the interpretive pitfalls practitioners must navigate. Whilst straightforward viruses such as influenza (EIV), alpha herpesviruses (EHV-1 and EHV-4), equine arteritis virus (EAV) and rhinoviruses can generally be attributed to disease, gamma herpesviruses (EHV-2 and EHV-5) complicate interpretation because they frequently colonise healthy horses, making positive results potentially misleading without careful clinical correlation. Beyond simple detection, quantitative PCR and genotyping now provide additional diagnostic value—viral load data for EHV-1 and EHV-4 indicate disease state, whilst EIV and EHV-1 genotyping informs virulence assessment and outbreak management strategies. Practitioners should therefore interpret PCR results within the full clinical context, considering patient status, sampling methodology and sample type, ensuring that diagnostic findings translate into proportionate biosecurity protocols and targeted medical interventions rather than unnecessary blanket approaches.
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Practical Takeaways
- •Do not assume a positive PCR result equals the cause of respiratory disease—integrate molecular findings with clinical signs, sample type, and patient status before diagnosing or treating.
- •Be aware that EHV-2 and EHV-5 are commonly found in healthy horses; their detection alone does not confirm disease causality and may represent latent or carrier status.
- •Request viral load quantitation (for EHV-1/4) and genotyping (for EIV/EHV-1) when managing outbreaks, as this information guides appropriate biosecurity measures and treatment decisions.
Key Findings
- •PCR-based molecular diagnostics are now preferred over traditional microbiology methods for rapid diagnosis of equine respiratory viruses due to superior speed, reliability, and sensitivity.
- •Interpretation of PCR results requires careful consideration of clinical status, sample type, assay used, and biological relevance, as positive results do not always indicate causality.
- •Gamma herpesviruses (EHV-2, EHV-5) are frequently detected in both diseased and healthy horses, making diagnostic interpretation challenging despite well-established host relationships.
- •Absolute quantitation of EHV-1 and EHV-4, and genotyping of EIV and EHV-1, provide additional information about viral state and virulence relevant to outbreak management and biosecurity decisions.