West Nile Virus can Threaten Horse Health this Fall

It’s not too late to help protect against the spread of disease during peak mosquito season

FLORHAM PARK, N.J., Aug. 19, 2014 — July through October coincides with peak mosquito activity, which can place your horse at the highest risk of contracting West Nile virus (WNV) during this time of year.1 However, with the right vaccine and preventive measures, it’s not too late for horse owners to help protect their horses against this life-threatening disease.

WNV is transmitted by mosquitoes — which feed on infected birds — to horses, humans and other mammals. Last year, the United States reported 395 West Nile virus cases in horses.2 Texas and Oklahoma topped the charts with 69 and 41 cases, respectively.2

The number of reported WNV veterinary cases fell from 1,121 in 2006 to 157 in 2010, and the decline is said by health experts to reflect both vaccination and naturally acquired immunity.3-5

“It is a good sign that the number of cases has declined over the last decade,” said Kevin G. Hankins, DVM, senior veterinarian, Equine Veterinary Operations, Zoetis. “However, recent news reports of both human and equine cases indicate this disease is still a risk — especially during this time of year.”6

Vaccination remains the most effective way to help protect horses against West Nile and other mosquito-borne diseases, such as Eastern equine encephalomyelitis (EEE) and Western equine encephalomyelitis (WEE).

Researchers recently tested horses' response to six West Nile virus vaccination regimens and found some substantial differences in their immune responses.7 While all of the vaccinated horses demonstrated an initial immune response, by Day 28, the antibody response of the horses vaccinated with WEST NILE-INNOVATOR® was four times higher than those vaccinated with the one-dose, big combination vaccines indicated for WNV.7

If your horse has not been vaccinated or is overdue for vaccination, it’s not too late to help protect it against this life-threatening disease with WEST NILE-INNOVATOR and a combination of other booster vaccines. This added protection can help your horse stay healthy.

“We thought that WEST NILE-INNOVATOR would produce a higher immune response than the large one-dose combination West Nile vaccines but did not realize it would be nearly four times higher,” Dr. Hankins said.7

West Nile is considered a core vaccination requirement, along with vaccinations for EEE, WEE, tetanus and rabies, according to the American Association of Equine Practitioners guidelines.3

“We have a disease that is here to stay, an effective vaccine but no treatment in the case of infection,” Dr. Hankins said. “That makes vaccination a cheap insurance policy.”

In conjunction with vaccination, use good techniques for managing mosquitoes and avoiding peak mosquito time. This includes:

• Destroying any mosquito breeding habitats by removing all potential sources of stagnant water
• Cleaning and emptying any water-holding container, such as water buckets, water troughs and plastic containers, on a weekly basis
• Apply insect repellents or bring horses inside during the peak mosquito feeding hours between dusk and dawn

Remember, WNV does not always lead to signs of illness. In horses that do become clinically ill, the virus infects the central nervous system and might cause symptoms such as loss of appetite and depression. Other clinical signs can include fever, weakness or paralysis of hind limbs, impaired vision, ataxia, aimless wandering, walking in circles, hyper-excitability or coma.8 Horse owners should contact a veterinarian immediately if they notice signs or symptoms of WNV infection in their horses, especially if they are exhibiting neurological signs. The case fatality rate for horses exhibiting clinical signs of WNV infection is approximately 33%.3

By providing proper vaccination and helping to manage mosquito populations, horse owners can do their part to help prevent WNV infections.  

For more information on WEST NILE-INNOVATOR, visit westnileinnovator.com.

About Zoetis

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. In 2013, the company generated annual revenues of $4.6 billion. With approximately 9,800 employees worldwide at the beginning of 2014, Zoetis has a local presence in approximately 70 countries, including 27 manufacturing facilities in 10 countries. Its products serve veterinarians, livestock producers and people who raise and care for farm and companion animals in 120 countries. For more information, visit https://www.zoetisUS.com.

Zoetis is the proud sponsor, with the Smithsonian Institution Traveling Exhibition Service, the American Veterinary Medical Association and the American Veterinary Medical Foundation, of the mobile educational exhibit Animal Connections: Our Journey Together. Families visiting the exhibit will explore the vast bonds between people and animals and learn about the important role veterinarians play in protecting animal and human health.

For further information, Contact:

Wendy Irvine

Amy Schendel
Bader Rutter

1Reed SM, Bayly WM, Sellon DC. Equine Internal Medicine, 3rd Ed. WB Saunders Co., Philadelphia, PA, 2010; 630.
2 U.S. Department of Interior. U.S. Geological Survey. Disease Maps 2013. Available at: http://diseasemaps.usgs.gov/2013/wnv_us_veterinary.html. Accessed August 19, 2014.
3 American Association of Equine Practitioners. Core Vaccination Guidelines. 2008. Available at: http://www.aaep.org/-i-165.html. Accessed August 19, 2014.
4 U.S. Department of Interior. U.S. Geological Survey. Disease Maps 2010. Available at: http://diseasemaps.usgs.gov/2010/wnv_us_veterinary.html. Accessed August 19, 2014.
5 U.S. Department of Interior. U.S. Geological Survey. Disease Maps 2006. Available at: http://diseasemaps.usgs.gov/2006/wnv_us_veterinary.html. Accessed August 19, 2014.
6 Centers for Disease Control and Prevention. West Nile Virus Activity by State – United States, 2014 (as of August 12, 2014). Available at: http://www.cdc.gov/westnile/statsMaps/preliminaryMapsData/activitystatedate.html. Accessed August 19, 2014.
7 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.
8 Pennsylvania’s West Nile Virus Control Program. What Horse Owners Should Know About West Nile Virus. 2000. Available at: http://www.westnile.state.pa.us/animals/horses.htm. Accessed August 19, 2014.



Mon–Fri, 8:30am–6:30pm ET

This site is intended for U.S. Animal Healthcare Professionals. The product information provided in this site is intended only for residents of the United States. The products discussed herein may not have marketing authorization or may have different product labeling in different countries. The animal health information contained herein is provided for educational purposes only and is not intended to replace discussions with an animal healthcare professional. All decisions regarding the care of a veterinary patient must be made with an animal healthcare professional, considering the unique characteristics of the patient.

All trademarks are the property of Zoetis Services LLC or a related company or a licensor unless otherwise noted. ©2022 Zoetis Services LLC. All rights reserved.