11/21/2025
*EHV-1 Outbreak Update 11/21/25
Equine herpesvirus-1 (EHV-1) is the virus causing this outbreak. While EHV-1 most commonly causes respiratory disease, some strains cause outbreaks of neurologic disease. EHV-1 causes neurologic signs as a result of inflammation of the blood vessels and activation of blood coagulation within the brain and spinal cord. Neurologic signs occur as a result of a lack of blood flow and resulting damage to the brain or spinal cord; this disease manifestation is known as Equine Herpesvirus Myeloencephalopathy (EHM). Classic clinical signs of EHM include fever, swelling/stocking up of the limbs, hindlimb weakness, and urine dribbling. Some horses are more severely affected and display behavior changes, signs of cranial nerve dysfunction, seizures, and inability to stand. While EHM is a serious disease, the majority of cases are not fatal. In most outbreaks of EHM, 60-70% of affected horses recover with treatment and supportive care. Veterinary evaluation and isolation of exposed or affected horses is crucial.
