Horse Owners Urged to Ensure Vaccinations are Up to Date

With warm weather gathering and mosquito season under way, 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 severely when infected with either West Nile virus (WNV) and Eastern equine encephalomyelitis (EEE), which are spread by mosquitoes and can be fatal to horses, said Delaware State Veterinarian Heather Hirst, DVM, MS, who heads the Delaware Department of Agriculture's Poultry and Animal Health Section.

"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.

Delaware's last confirmed equine case of EEE was in 2005, and its last confirmed equine case of WNV was in 2003.

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

  • Clinical signs for WNV include flulike conditions where the horse seems mildly anorexic and depressed; fine and coarse muscle and skin fasciculations (twitching); hyperesthesia, or hypersensitivity to touch and sound; changes in mentation (mentality), when horses look like they are daydreaming or "just not with it"; occasional somnolence (drowsiness); propulsive walking (driving or pushing forward, often without control); and "spinal" signs, including asymmetrical weakness. Some horses show asymmetrical or symmetrical ataxia (incoordination on one or both sides, respectively). Equine mortality rate can be as high as 30-40%.
  • Clinical signs for 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 fatality rate for EEE-affected horses is 75-95%. The course of EEE can be swift, with death occurring two to three days after onset of clinical signs despite intensive care. Horses that survive might have long-lasting impairments and neurologic problems.

Owners should consult with their veterinarians about the WNV and EEE vaccinations, as well as vaccinations for herpesvirus (rhinopneumonitis), equine 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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