From the Nevada Department of Agriculture: 

The Nevada Department of Agriculture’s (NDA) Animal Disease and Food Safety Laboratory reports a West Nile Virus positive mosquito pool in Pershing County. The mosquitos were collected south of Rye Patch Dam at the end of July.
To date, the lab has tested more than 2,400 mosquito pools statewide. West Nile Virus positive pools were previously identified in Washoe County (1) and Clark Co (65). Mosquitos infected with Saint Louis Encephalitis Virus were also identified in Clark County. 
The statewide mosquito surveillance program is based on the work of vector control agencies in Washoe, Clark, Churchill, Douglas and Lyon Counties. Surveillance in rural counties is conducted through the State Entomologist’s office at the NDA. 
“All samples are submitted to us for testing for three endemic arbo-viral diseases, West Nile Virus, Saint Louis Encephalitis Virus and Western Equine Encephalitis Virus,” Dr. Anette Rink, DVM and Laboratory Supervisor at the NDA, said. “All of these viruses can cause severe disease and death in humans, so we take all virus testing in our lab very seriously.”
West Nile Virus has been endemic in Nevada since 2004. Mosquito season is expected to end with the first killing frost in October. However, while the current temperatures persist, all Nevada residents should take precautions such as eliminating mosquito-breeding sites around houses and barns, use insect repellents and keep horses vaccinated against West Nile Virus other equine viruses.

From the Nevada Department of Agriculture