New Mexico and Montana joined the list of states affected by West Nile virus (WNV) Thursday when they announced their first equine cases. A New Mexico ranch horse from Tucumcari, in the eastern part of the state, did not survive WNV, and was not vaccinated against the illness. Initial test results received from the National Veterinary Services Laboratories in Ames, Iowa, on Aug. 22 showed that a Shepherd, Mont., horse has WNV. The unvaccinated horse is responding to supportive treatment.

Thurman Reitz, DVM, assistant state veterinarian at the New Mexico Livestock Board, said, “We have one case for sure, and I wouldn’t be surprised if we have some more.” Officials have not found any birds or mosquitoes infected with the virus in the state.

“Most areas of the state don’t have a lot of mosquitoes.” said Reitz, “This was kind of an unusual situation.”

Reitz explained that there was a dried-up flatland lake, or “playa lake,” on the property where the affected horse was kept with its herdmates, and there were a few trees near the lake. “The horses come down and hang around the trees in the middle of the day, and apparently there were mosquitoes around this dried-up lake,” said Reitz. “These were probably the only trees for 40 miles, and the birds came to these trees, too. So, there were birds, mosquitoes, and horses, and I guess that was a bad combination