Virginia Owners Advised to Vaccinate Horses

For the vaccine to be effective it must be handled and administered properly and be given at least two weeks before the horse is exposed to the virus.

Photo: Erica Larson, News Editor

Mosquito season will begin soon in Virginia. That means it’s time for owners to start thinking about vaccinating horses against mosquito-borne illnesses such as West Nile virus (WNV) and Eastern equine encephalitis (EEE).

Additionally, while rabies is not a mosquito-borne disease, it’s a fatal condition that also requires an annual vaccination. Last year three horses died of rabies in Virginia, one each in Fairfax, Frederick, and Loudoun Counties.

The Virginia Department of Agriculture and Consumer Services (VDACS) is urging all horse owners to check with their veterinarians for vaccination recommendations for their animals. In 2015, Virginia only had one confirmed case of WNV (in Orange County) and three of EEE (unrelated cases from July through October, all in Chesapeake), although many surrounding states had a much higher incidence of cases.

“Timely vaccination has been shown to decrease WNV and EEE disease incidence drastically,” said Richard Wilkes, DVM, state veterinarian at the VDACS, “and that may explain why cases are down in Virginia. Without vaccination, we would expect to see many more infected horses, so we still urge horse owners to consider EEE and WNV vaccination. We believe that in most cases, private veterinarians will recommend them for their clients.”

The WNV and EEE vaccines are effective for six to 12 months, so horses should be vaccinated at least annually. In areas where the disease occurs frequently, most veterinarians recommend vaccination every six months. For the vaccine to be effective it must be handled and administered properly and be given at least two weeks before the horse is exposed to the virus. Additionally, to stimulate full immunity, horses must be vaccinated twice, about 30 days apart, the first year they are vaccinated.

Other mosquito-borne disease prevention methods include eliminating standing water breeding sites for mosquitoes, using insect repellents, removing animals from mosquito-infested areas during peak biting times (usually dusk to dawn), and turning off the lights in and around the barn at night.

Wilkes also suggests that owners check about rabies vaccinations for their horses. “Three cases are three too many,” he added, “because the disease is 100% fatal but vaccination is very effective” in reducing disease incidence.

In addition to taking measures to decrease the likelihood that horses will be exposed to rabies, routine rabies vaccination is a very important aspect of disease prevention. Vaccinating horses annually can prevent rabies in both horses and humans. Humans can become infected with rabies by handling a rabid horse but cannot become infected with EEE or WNV by handling an infected horse, nor can a horse acquire the virus from another infected horse. The presence of an infected horse in the area indicates that mosquitoes carrying the EEE or WNV viruses are present, however, and those insects pose a threat to both humans and horses.

All three of these diseases—EEE, WNV, and rabies—cause neurologic signs in horses, such as staggering, circling, depression, loss of appetite, and sometimes fever and blindness. The mortality varies from disease to disease, with 30% of WNV-infected horses dying, to a 90% death rate for EEE, and 100% mortality for rabies cases. There are no specific and proven cures for these diseases, but veterinarians can provide supportive therapy to treat clinical signs of EEE and WNV and keep horses from injuring themselves, which is successful in returning horses to health in some cases.

While owners are having their horses vaccinated, it’s also a good time to get the horse tested for equine infectious anemia (EIA); this is typically accomplished via a Coggins test. Virginia horse owners should be aware that “all horses assembled at a show, fair, race meet, or other such function or participating in any activity on properties where horses belonging to different owners may come into contact with each other in Virginia must be accompanied by a report of an official negative test for equine infectious anemia.”

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