angle-left Increased Risk for Equine West Nile Virus

Increased Risk for Equine West Nile Virus

Equine vaccination and proper management techniques help offer protection.
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From AQHA Corporate Partner Zoetis

The risk for West Nile virus remains. In 2016, there were 377 equine West Nile virus cases across the United States – an increase of 152 cases from 2015.1

Horses are at the highest risk for contracting West Nile virus during peak mosquito season, which occurs July through October in the United States.2 It’s not too late to help protect horses against this devastating disease. Veterinarians and horse owners continue to trust WEST NILE-INNOVATOR®. No other vaccine has protected more horses against West Nile.3

“Vaccination is extremely effective against West Nile virus and remains the most effective way to help protect horses against the disease,” said Kevin Hankins, DVM, senior veterinarian, Equine Technical Services, Zoetis.

When properly vaccinated, horses have shown to be 30 times less likely to contract West Nile.4

West Nile virus is transmitted by mosquitoes — which feed on infected birds — to horses, humans and other mammals. Dr. Hankins explains that the uptick in 2016 cases is likely due to the drought that occurred in 2015. Droughts can increase numbers of small, stagnant pools of water, presenting ideal breeding grounds for mosquitoes. During a drought, bird populations often decrease. As birds flock to wetter areas of the country, mosquitoes are left to feed on other warm-blooded animals nearby, such as horses.

When considering the 377 equine West Nile cases recorded across the United States in 2016,1 Dr. Hankins cautioned, “The numbers are likely much greater. Some states only report West Nile virus cases if the disease is presented in neurological form.”

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 virus than was produced by a big one-shot combination vaccine.5

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

  • Eliminate any mosquito-breeding habitats by removing all potential sources of stagnant water, such as unused troughs, wheelbarrows, ditches and tarps.
  • Hang fans throughout the barn where horses are stabled, as mosquitoes avoid moving air.
  • Clean and empty any water-holding containers on a weekly basis.
  • Apply insect repellent or bring horses inside from dusk to dawn, which is peak mosquito feeding hours.

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 percent of horses that exhibit clinical signs of disease.7

Don’t miss the opportunity to help protect your horses against this devastating disease. To learn more about proper equine vaccination and WEST NILE-INNOVATOR, please visit



1 2016 Summary of West Nile Virus Equine Cases in the United States. USDA-APHIS. Accessed April 24, 2017.

2 Reed SM, Bayly WM, Sellon DC. Equine Internal Medicine, 3rd ed. Philadelphia: WB Saunders Co., 2010;630.

3 Data on file. MDI sales data for WEST NILE-INNOVATOR as of 12/31/16, Zoetis Inc.

4 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.

5 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.

6 What Horse Owners Should Know About West Nile Virus. Pennsylvania’s West Nile Virus Control Program website. Accessed April 25, 2017.

7 Core Vaccination Guidelines. American Association of Equine Practitioners website. Accessed April 25, 2017.


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