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Say 'neigh' to west Nile virus, eastern equine encephalitis

As summer turns to fall, most of the U.S. officially enters peak mosquito season. And with peak mosquito season comes a rise in mosquito-borne illnesses, including West Nile Virus and Eastern Equine Encephalitis (EEE).

Because these vector-borne diseases affect multiple species of animals, including humans, Dr. Amanda Trimble, a clinical assistant professor of equine internal medicine at the Texas A&M College of Veterinary Medicine & Biomedical Sciences, explains how West Nile Virus and EEE affect horses and provides tips to owners for helping their equine companions prevent these diseases.

What are West Nile Virus and EEE?

While West Nile Virus and EEE are viral infections that most commonly affect horses, humans, and birds, neither is zoonotic (meaning you can't get it from your horse), according to Trimble.

"Neither disease is contagious directly to humans from horses and vice versa; however, cases seen in either species may indicate that the diseases are present in the local mosquito population," Trimble said. "Both viruses need mosquito vectors to be spread, meaning that a mosquito must collect blood from an infected carrier of the virus—typically a bird—and then bite a horse or human in order for the disease to spread."

Because West Nile Virus and EEE depend on mosquitoes to spread, Trimble said it is important for horse owners to be mindful of mosquito season.

"Peak incidence follows mosquitoes—which typically peak between July and October for most of the United States," she shared. "But because Texas is always warm, mosquito season never really ends."

As a result, Trimble recommends Texans help protect their horses from West Nile Virus and EEE year-round.

How do West Nile Virus and EEE affect horses?

Both viruses can be fatal for horses.

"About one-third of affected horses—typically those that are unvaccinated—may die from West Nile Virus, while more than 90% of unvaccinated horses die from an EEE infection," Trimble said. "With both, disease and clinical signs may still occur in horses that are vaccinated but are usually much less severe. However, horses that survive may have permanent neurological deficits."

Trimble recommends owners contact a veterinarian if they suspect their horse has either virus based on the following symptoms:

West Nile Virus symptoms include:

• Lethargy
• Fever
• Anorexia (low appetite)
• Neurological signs such as sudden onset tremors (especially in the muzzle), weakness, or uncoordinated walking, stumbling, or falling
• Recumbency, or lying down without being able to rise

EEE symptoms include:

• Lethargy
• Fever
• Anorexia
• Neurological signs including an inability to swallow, tremors, head pressing, seizures, circling, blindness, rapid behavior changes, and uncoordinated walking, stumbling, or falling
• Recumbency

Trimble said a veterinary team can provide supportive care to a horse diagnosed with either virus.

"Care is largely supportive. For non-severe cases, this may include anti-inflammatories and keeping the horse hydrated and eating," Trimble said. "More severe cases, which includes horses with severe neurological signs or recumbency (can't get up), may need to be hospitalized or referred to a facility that can provide intravenous fluids and more intensive medical care."

Protecting horses from West Nile Virus and EEE

Protecting horses from West Nile Virus and EEE starts with creating a prevention plan with a veterinarian, according to Trimble, including vaccination. Trimble recommends horses receive the vaccine twice a year in states like Texas where mosquitoes are present year-round.

"Both diseases are considered "Equine Core Vaccines' by the American Association of Equine Practitioners and all horses should receive them," Trimble said. "These diseases do not need other horses to be spread, and they can cause severe and potentially fatal neurological disease if a horse is not properly protected from them. The vaccines are safe and effective and can help decrease the spread and severity of disease."

In addition to keeping horses up-to-date on their core vaccinations, Trimble recommends implementing environmental management strategies as well. These strategies can help protect your horse by reducing the mosquito population in their environment and include:

• Eliminating standing water, which is a breeding ground for mosquitoes
• Installing mosquito lights or zappers
• Using fly sheets or boots
• Applying fly spray and other insect repellent frequently
• Adding a supplement containing garlic to horses' feed may be helpful
• Keeping horses inside at dawn, dusk, and at night
• Cleaning water buckets and tanks at least once daily
• Running fans
• Introducing mosquito-eating fish to ponds and lakes

"Vaccinating horses and proper mosquito management should decrease risk of fatal disease substantially," Trimble said.

Finally, as both diseases can affect humans, although rarely, Trimble recommends owners also learn how to protect themselves from mosquito bites by following the Centers for Disease Control and Prevention guidelines.

Keeping mosquito safety top of mind through the changing seasons will help ensure the entire family—including horses—is happy, healthy, and protected from West Nile Virus and EEE.