The season approaches for mosquitoes as well as horse shows and events. Oregon State Veterinarian, Brad LeaMaster, DVM, PhD, of the Oregon Department of Agriculture, advised owners on May 21 to protect their horses against two viral threats by vaccinating against West Nile virus (WNV) and taking steps to prevent equine herpesvirus-1 (EHV-1).

“It’s important for horse owners to vaccinate animals for West Nile Virus before the mosquito season kicks into high gear,” says LeaMaster. “The vaccine provides good protection and is available through local veterinarians.”

Infected wild birds are the source of WNV. Mosquitoes bite infected birds and then can potentially transmit the infection to horses and humans. The disease does not transmit from horse to horse or human to human. A bite by an infected mosquito is the only known route of transmission. A low percentage of mosquitoes carry the virus and a low percentage of horses bitten by infected mosquitoes become ill. But a horse showing signs is a serious situation. The disease causes brain inflammation and about one-third of affected horses die. Clinical signs include stumbling, lack of coordination, weakness in the legs, depression, muscle twitching, and death.

Insect control on individual animals also provides a good preventative measure along with reducing mosquito breeding sites. Any source of stagnant water can breed mosquitoes