Owners Urged to Ensure Horses' Vaccinations are Up to Date

Owners Urged to Ensure Horses' Vaccinations are Up to Date

“Vaccination is a simple and cost-effective way of preventing these diseases—far cheaper than treating them,” Hirst said.

Photo: Kevin Thompson/The Horse

With warm weather here and mosquito season under way, Delaware horse owners are being advised to make certain their equids’ vaccinations are current to protect against the threat of two potentially fatal diseases.

Unvaccinated horses suffer most severely from both West Nile virus (WNV) and Eastern equine encephalomyelitis (EEE), which are spread by infected mosquitoes and can be fatal, said Delaware State Veterinarian Heather Hirst, DVM, who heads the Delaware Department of Agriculture’s Poultry and Animal Health Section. Delaware had two confirmed equine cases of EEE and six confirmed equine cases of WNV in 2013.

“Vaccination is a simple and cost-effective way of preventing these diseases—far cheaper than treating them,” Hirst said. “Horse owners should take full precautions to keep their horses safe, and be on the alert for signs of infection.”

Both horses and humans can contract WNV and EEE if bitten by a mosquito carrying the virus, but it is important to note that the viruses cannot be transmitted between horses or from horses to people. The viruses normally exist in a cycle between mosquitoes and birds, but occasionally EEE can be transmitted from mosquitoes to mammals.

Hirst said horse owners should contact their veterinarian immediately if they suspect their horse could be showing signs of WNV or EEE.

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.

Clinical signs of 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%.

Owners should consult with their veterinarians about the WNV and EEE vaccinations, as well as vaccinations for herpesvirus (rhinopneumonitis), influenza, rabies, and tetanus, among others, Hirst said.

Horse owners can also help during mosquito season by keeping horses inside during dawn and dusk, which are peak mosquito times, and using topical insect repellents labeled for use on horses, Hirst said.

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