Infectious Disease | ID Perspective

Safeguarding Equine Health: Advocating for West Nile Vaccination and Mosquito Control

By Kevin Hankins, DVM, MS, MBA

As summer intensifies and temperatures rise, we’re reminded of the impending threats posed by mosquito-borne illnesses—especially after West Nile virus (WNV) and Eastern equine encephalomyelitis (EEE) surged over the past two years. As veterinarians, it falls on us to arm our clients with the knowledge and tools necessary to protect horses from this potentially deadly disease.

COMMUNICATE EARLY
It’s important that horse owners understand the risks of WNV and that it’s a viral infection primarily transmitted through mosquitos that can affect both horses and humans.

WNV can manifest in horses with varying degrees of severity, from mild symptoms like fever, depression, weakness, muscle tremors and loss of appetite to more concerning neurological signs such as ataxia, head-pressing, difficulty swallowing and seizures. In severe cases, the infection may be fatal. According to the American Association of Equine Practitioners (AAEP), this virus has been shown to be fatal in 33% of horses that exhibit clinical signs of disease.1

Spring and late summer are the two crucial periods for taking WNV preventive measures.

MULTI-FACETED STRATEGY
Remind horse owners about effective mosquito-reduction techniques, including:

• Breeding ground reduction: Eliminate stagnant water sources that mosquitoes thrive in. Regularly clean water containers and maintain proper drainage to hinder mosquito reproduction.
• Mechanical and chemical solutions: Employ fans, electrical insect deterrence devices, mosquito-proof screens and traps. Larvicides approved for animal use can quell stagnant water in areas where horses reside.
• Mosquito repellents: Recommend approved equine-specific repellents designed to help provide an additional layer of protection, especially during peak mosquito feeding hours.
• Physical barriers: Outfit horses with fly sheets and masks, not only to deter mosquito bites but also to shield against other vector-borne ailments and skin irritations.

EMPOWER PARTNERSHIP
Encourage horse owners to work with you to tailor vaccination schedules based on individual risk profiles, age and prior vaccine history. Stress the importance of timely booster vaccinations and illustrate the potential life-saving impact of equine immunization.

Research underscores that vaccination is the best defense against WNV,2-4 with studies indicating that vaccinated horses are potentially 30 times less likely to contract the virus.2

VACCINATION
West Nile-Innovator®: The West Nile-Innovator line of vaccines protects against WNV, EEE, Western equine encephalomyelitis (WEE), Venezuelan equine encephalomyelitis (VEE) and tetanus.

• In a study, West Nile-Innovator was demonstrated to be 96% effective in immunologically naive horses3
• If a client’s horse received core vaccinations in the spring, schedule a booster to help provide additional protection

Core EQ Innovator®: Core EQ Innovator is the first and only vaccine to help protect horses against all five potentially fatal core equine diseases in one injection.

• If a horse didn’t receive vaccination against these five core diseases in the spring, recommend scheduling it now
• Fall boosters may also be considered for horses at higher risk

The Zoetis Equine Immunization Support Guarantee covers reasonable diagnostic and treatment costs up to $5,000 if a horse properly vaccinated by a veterinarian with a Zoetis vaccine contracts one of the following corresponding equine diseases: WNV, EEE, WEE, rabies, tetanus, flu, rhino or VEE.

REFERENCES
1. American Association of Equine Practitioners. Adult horse vaccination chart. https://aaep.org/guidelines/vaccination-guidelines/core-vaccination-guidelines. Accessed April 11, 2025.
2. 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.
3. Epp T, Waldner C, Townsend HGG. A case-control study of factors associated with development of clinical disease due to West Nile virus. Equine Vet J. 2007;39:498-503.
4. Cortese V, Hankins K, Holland R, et al. Serologic responses of West Nile virus seronegative mature horses to West Nile virus vaccines. J Equine Vet Sci. 2013;33:1101-1105.

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To learn more, visit the West Nile-Innovator and Core EQ Innovator product pages.