A Deschutes County horse has tested positive for West Nile Virus (WNV), marking the first detection of the disease in Oregon horses for the 2016 season. The affected horse is a 14-year old mare with no history of vaccination for WNV. The horse is under veterinary care and is responding to treatment.


Last year, six horses in Oregon were confirmed to be infected with WNV.

“Horses become infected with the virus the same way humans become infected, by being bitten by infected mosquitoes,” says Brad LeaMaster, State Veterinarian with the Oregon Department of Agriculture. “I would like to take this opportunity to remind horse owners to contact their local veterinarian regarding proper West Nile Virus vaccination protocols during this time of increased risk.”

Along with vaccination, horse owners can protect their animals by controlling mosquitoes and mosquito breeding areas. Approved repellents can also provide temporary protection.

WNV causes encephalitis and affects the central nervous system. One of the most common signs of WNV in horses is weakness or incoordination in the hindquarters. There may be stumbling, leaning to one side, and toe dragging. As the disease progresses, paralysis may follow. Fever is sometimes evident, as well as changes in behavior such as depression and/or uneasiness. Horse owners who suspect WNV infection should contact their veterinarian immediately. Early treatment can often decrease the severity of the disease. About 30-40 percent of horses that show signs of the illness will die. The majority of WNV cases in horses occur in the months of August and September, which corresponds to peak mosquito activity.