The Oregon Department of Agriculture (ODA) received six confirmed reports of West Nile Virus (WNV) diagnosed in Oregon horses in the past two weeks. One additional suspected case is under investigation. The affected horses live in multiple counties throughout the state: Umatilla, Malheur, and Klamath. None of the infected horses were recently vaccinated against WNV, and most of the horses have never been vaccinated for WNV.
Numerous additional WNV cases have also been reported recently in Washington, Idaho, and California near the Oregon border. Therefore, ODA advises annual vaccination as an effective tool for preventing WNV infection in horses.
On September 9, 2021, Oregon State Veterinarian, Dr. Ryan Scholz, DVM, received a report that Equine Herpesvirus Myeloencephalopathy (EHV-1) was diagnosed in one horse and suspected in a second horse on a private farm in Linn County. A third horse on the same farm tested positive for EHV-1, with a fourth and fifth horse exposed. Two of the affected horses were euthanized. A preliminary investigation shows none of the five horses have been moved off the farm or in contact with other horses in the past four weeks. As a result, Dr. Scholz placed the farm under quarantine.
EHV-1 is highly contagious. While there are no known exposures linked to the Linn County farm, Dr. Scholz recommends that horse owners concerned about exposure monitor their horse's temperature and contact their veterinarian if a fever or clinical signs develop. EHV-1 testing is generally not advised in asymptomatic horses. More information is available from Equine Disease Communication Center (EDCC).
West Nile Virus and EHV-1 are both reportable diseases in Oregon. Veterinarians must report suspected cases to the Oregon State Veterinarian by calling 503-986-4680.