Vt. State Vet Urges Horse Owners to Vaccinate for EEE, WNV

Vt. State Vet Urges Horse Owners to Vaccinate for EEE, WNV

Vaccination is the most effective tool for reducing the risk of EEE and WNV in horses.

Photo: Erica Larson, News Editor

Spring is here, and with its arrival comes the need for horse-owning Vermonters to ensure their companions are protected from diseases transmitted by mosquitoes, including Eastern equine encephalitis (EEE) and West Nile virus (WNV).

“This is the time of the year when horse owners should be consulting with their veterinarians to ensure that their horses are appropriately vaccinated for EEE and WNV”, says Kristin Haas, DVM, Vermont state veterinarian. “A horse’s susceptibility to EEE and WNV infection is not linked to travel to shows, fairs, or other commingling events. We know that both viruses are present in Vermont, so even horses that spend the majority of their time on isolated properties are susceptible and should be vaccinated.”

A viral disease, EEE affects the central nervous system and is transmitted to horses by infected mosquitoes. Clinical signs of EEE include moderate to high fever, depression, lack of appetite, cranial nerve deficits (facial paralysis, tongue weakness, difficulty swallowing), behavioral changes (aggression, self-mutilation, or drowsiness), gait abnormalities, or severe central nervous system signs, such as head-pressing, circling, blindness, and seizures. The course of EEE can be swift, with death occurring two to three days after onset of clinical signs despite intensive care; fatality rates reach 75-80% among horses. Horses that survive might have long-lasting impairments and neurologic problems.

WNV is a viral disease transmitted to horses by infected mosquitoes. Clinical signs for WNV include flulike signs, where the horse seems mildly anorexic and depressed; fine and coarse muscle and skin fasciculations (twitching); hyperesthesia (hypersensitivity to touch and sound); changes in mentation (mentality), when horses look like they are daydreaming or "just not with it"; occasional drowsiness; propulsive walking (driving or pushing forward, often without control); and "spinal" signs, including asymmetrical weakness. Some horses show asymmetrical or symmetrical ataxia (incoordination). Equine mortality rate can be as high as 30-40%.

Although vaccination is the most effective tool for reducing the risk of EEE and WNV in horses, owners can also protect their equids from infection by using an acceptable insect repellent seasonally and mechanical barriers such as fly sheets and masks. Changing out water troughs regularly and removing other items that hold water will help to reduce mosquito breeding areas.

Cases of EEE and WNV diagnosed in Vermont horses must be reported to the Office of the State Veterinarian.

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