Equine West Nile Threat Increases During Peak Mosquito Season

Horses are at highest risk of contracting West Nile virus during peak mosquito activity, which occurs July through October in the United States.1 However, there’s still an opportunity to help protect horses against this life-threatening disease. Veterinarians and horse owners continue to trust WEST NILE-INNOVATOR, the first vaccine on the market when West Nile struck the United States, to help protect their horses.2

“West Nile continues to be a major concern for the equine community, so it’s critical that horse owners and veterinarians remember to vaccinate horses annually against this deadly disease,” said Kevin Hankins, DVM, senior veterinarian, Zoetis Equine Technical Services. “A horse that is not vaccinated annually is still very much at risk, which is why we continue to see a great number of West Nile cases in unvaccinated horses.”

West Nile virus is transmitted by mosquitoes–which feed on infected birds–to horses, humans and other mammals. Vaccination remains the most effective way to help protect horses against West Nile and other mosquito-borne diseases. If vaccinated, horses have shown to be 30 times less likely to contract West Nile.3

For horses that have not been vaccinated or are overdue for vaccination, WEST NILE-INNOVATOR can help provide the added protection horses need to stay healthy. A study showed that separate administration of WEST NILE-INNOVATOR and FLUVAC INNOVATOR generated four times the immune response to West Nile than was produced by a big one-shot combination vaccine.4

In conjunction with vaccination, proper horse management techniques can help prevent West Nile cases, such as:

  • Destroying any mosquito-breeding habitats by removing all potential sources of stagnant water;
  • Cleaning and emptying any water-holding containers, such as water buckets, water troughs and plastic containers, on a weekly basis;5 and
  • Applying insect repellent or bringing horses inside during the peak mosquito feeding hours of dusk to dawn.

West Nile does not always lead to signs of illness in horses. For horses that do become clinically ill, the virus infects the central nervous system and may cause symptoms such as loss of appetite and depression. Other clinical signs may include fever, weakness or paralysis of hind limbs, impaired vision, ataxia, aimless wandering, walking in circles, hyperexcitability or coma.6 If horse owners notice signs or symptoms of West Nile infection in their horses, they should contact a veterinarian immediately. West Nile virus is fatal in 33% of horses that exhibit clinical signs of disease.7

To learn more about proper vaccination and WEST NILE-INNOVATOR, please visit

Zoetis (zō-EH-tis) is the leading animal health company, dedicated to supporting its customers and their businesses. Building on more than 60 years of experience in animal health, Zoetis discovers, develops, manufactures and markets veterinary vaccines and medicines, complemented by diagnostic products and genetic tests and supported by a range of services. Zoetis serves veterinarians, livestock producers and people who raise and care for farm and companion animals with sales of its products in more than 100 countries. In 2015, the company generated annual revenue of $4.8 billion with approximately 9,000 employees. For more information, visit

1 Reed SM, Bayly WM, Sellon DC. Equine Internal Medicine, 3rd ed. Philadelphia: WB Saunders Co. 2010;630.
2 Data on file. MDI sales data for WEST NILE-INNOVATOR as of 12/31/15, Zoetis LLC.
3 Epp T, Waldner C, West K. Efficacy of vaccination for West Nile virus in Saskatchewan horses, in Proceedings. 51st
Annual Convention of the AAEP 2005;180-182.
4 Cortese V, Hankins K, Holland R, Syvrud K. Serologic Responses of West Nile Virus Seronegative Mature Horses to West Nile Virus Vaccines. J Equine Vet Sci. 2013;33:1101-1105.
5 West Nile Virus. Florida Department of Agriculture and Consumer Services, Division of Animal Industry website. Accessed May 11, 2016.
6 What Horse Owners Should Know About West Nile Virus. Pennsylvania’s West Nile Virus Control Program website. Accessed May 11, 2016.
7 Core Vaccination Guidelines. American Association of Equine Practitioners website. Accessed May 11, 2016.






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