European College of Equine Internal Medicine consensus statement on equine flaviviridae infections in Europe.
Authors: Cavalleri Jessika-M V, Korbacska-Kutasi Orsolya, Leblond Agnès, Paillot Romain, Pusterla Nicola, Steinmann Eike, Tomlinson Joy
Journal: Journal of veterinary internal medicine
Summary
# European Flavivirus Infections in Horses: Consensus Guidance for European Practitioners Five flaviviruses and hepaciviruses now circulate across Europe with documented pathogenicity in equids—West Nile virus, tick-borne encephalitis virus, Usutu virus, Louping ill virus, and equine hepacivirus—transmitted either by mosquitoes or ticks depending on the agent. A 2022 European College of Equine Internal Medicine consensus statement synthesised current evidence on the clinical presentation, diagnosis, and management of these infections to provide clinically actionable recommendations for practitioners across the continent. West Nile virus and tick-borne encephalitis virus represent the primary neurological threats, capable of inducing severe encephalitis, whilst Louping ill virus causes rare but documented encephalitic cases in the British Isles; equine hepacivirus, by contrast, typically manifests as mild to chronic hepatitis of variable severity. Diagnosis relies primarily on serological testing, though cross-reactivity between flaviviruses necessitates virus neutralisation testing as the gold standard for definitive differentiation, whilst hepacivirus is confirmed through RT-PCR of serum or liver tissue. With no direct antivirals currently available for equine flaviviral or hepaciviral infections, management remains supportive, though three West Nile virus vaccines are licensed in the EU—making geographic surveillance and risk assessment critical considerations for practitioners, particularly given the documented expansion patterns of these pathogens across European regions.
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Practical Takeaways
- •Consider flavivirus infections in the differential diagnosis of equine neurological or hepatic disease depending on geographic location and season; West Nile and tick-borne encephalitis cause neurological signs while equine hepacivirus causes hepatitis
- •Request virus neutralization testing rather than standard serology to accurately differentiate between flavivirus infections, as cross-reactivity is common with serological methods
- •Implement supportive care for confirmed flavivirus or hepacivirus infections as no specific antiviral therapies exist; consider West Nile virus vaccination for horses in endemic or at-risk regions
Key Findings
- •Five Flaviviridae viruses circulate in Europe with different transmission routes: West Nile and Usutu via mosquitoes, tick-borne encephalitis and Louping ill via ticks, and equine hepacivirus via unknown route
- •West Nile virus and tick-borne encephalitis virus can cause encephalitis in horses, while equine hepacivirus causes mild to chronic hepatitis
- •Virus neutralization testing is the gold standard for differentiating between flavivirus infections, while hepacivirus is diagnosed by serum or liver RT-PCR
- •No direct antiviral treatments are currently available for flavivirus or hepacivirus infections in horses; three West Nile virus vaccines are licensed in the European Union