Based upon the travel history of the animal and the incubation period of the disease, the horse was likely exposed at an event in Ravalli County, Mt., earlier this month. The Montana Department of Livestock (MDOL) is currently working with event organizers to inform event participants of potential risk.

EHV-1 is naturally occurring in equine populations and can cause respiratory disease, abortion in mares, neonatal foal death, and/or neurologic disease. There are two types of the virus responsible for outbreaks in the United States: the neuropathogenic form and the wild type. The horse in question appears to be infected with the less virulent strain, which is not as likely to cause neurologic or severe clinical symptoms.

According to Assistant Montana State Veterinarian Dr. Tahnee Szymanski, the affected horse developed weakness, which progressed into recumbency (the inability to rise or stand) two weeks after attending the event. The infection was confirmed by blood and nasal swab samples