10 Facts About Equine West Nile Virus
Published on: 4/29/2025Key Takeaways
- West Nile virus (WNV), first detected in North America in 1999, is transmitted by mosquitoes and poses a major risk to horses–who account for 97% of all non-human mammalian cases.
- Horses typically show symptoms 3-15 days after infection, and the disease carries a 33% fatality rate.
- Over 25,000 U.S. equine cases have been reported, with risk peaking from July through October during heavy mosquito activity.
- Vaccinated horses are 30 times less likely to contract WNV, with vaccines offering nearly 100% protection when boosted properly.
- Spring vaccination combined with strong mosquito control measures provides the best defense against this deadly disease.
Your horse is part of your family, but unless he is vaccinated, he could be at risk for potentially deadly diseases like West Nile virus (WNV). As we prepare for mosquito season and the heightened risk of disease, be aware of these 10 important WNV facts.
- Africa, Eastern Europe and West Asia have long experienced the impact of WNV; however, the disease is fairly recent to North America with the first case diagnosed in 1999.
- West Nile virus is transmitted by mosquitoes - which feed on infected birds - to horses, humans and other mammals.
- Horses represent 97% of all reported non-human mammalian cases of WNV disease.
- Infected horses begin to show signs of disease as early as three to 15 days.
- More than 25,000 cases of WNV have been reported in U.S. horses.
- The disease presents a 33% fatality rate to horses.
- Disease risk increased in 2018, with 384 cases of equine WNV reported - nearly 80 cases more than in 2017.
- Horses are at the highest risk for contracting WNV during peak mosquito season - July through October.
- When properly vaccinated, horses have shown to be 30 times less likely to contract WNV.
- Vaccination provides horses with nearly 100% protection against WNV.
Vaccinate your horse in spring, before the onset of mosquito season, to offer your horse the best protection available against West Nile virus. The vaccines, regardless of brand, will booster the protection. Remember, vaccination in conjunction with established mosquito management techniques are key to helping keep animals safe from this dangerous disease.
Help protect your horse from West Nile virus:
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