Two unrelated cases of the neurological form of Equines Herpes Virus-1 (EHV-1) have been reported in Montana in the space of a week.
In the most recent case, a 6-year-old mare in Gallatin County tested positive for the virus.
The Montana Department of Livestock said it was not related to a case in Flathead County reported late last week.
“We have another case of EHV-1, but let me stress that there is no connection to the earlier case,” assistant state veterinarian, Dr Tahnee Szymanski, said.
“Fortunately, the Gallatin County case, like the Flathead case, appears to be an isolated event.”
The infected horse arrived in Montana three weeks ago from southern California. The horse began showing clinical signs of the virus last week. Test results received Saturday morning confirmed presence of the virus.
The horse is housed at a boarding and training facility, which is under quarantine, in Gallatin County. An encouraging sign, Syzmanski said, is that none of the other horses at the facility has shown any clinical signs of contracting the virus.
“The manager and trainers at the facility have been great to work with, and are letting all of their clients know about the incident,” Szymanski said.
In the Flathead County case, authorities said that, based on the travel history of the animal and the incubation period of the disease, the horse was likely exposed at an event in Ravalli County earlier in the month.
The department said it was working with event organizers to inform participants of the potential risk.
Szymanski said the affected horse developed weakness, which progressed into recumbency – inability to rise or stand – two weeks after attending the event. The infection was confirmed by blood and nasal swab samples.
An encouraging sign, she added, was that the index horse seems to be improving.
EHV-1 is naturally occurring in equine populations and may 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 US – the neuropathogenic form, and the wild type. The horse in Gallatin County, as well as the horse in Flathead County, appear to have been infected with the less virulent wild type.