Tests from two mosquito pools show the first presence of West Nile virus this year in Nevada.
The state Department of Agriculture says the positive samples were from pools in Lovelock.
West Nile is spread by mosquitoes biting humans after feeding on infected birds.
Health officials say few people bitten by an infected mosquito become seriously ill. They suggest wearing pants and long sleeves when mosquitoes are most active around dawn and dusk, and to use insect repellent to avoid being bitten.
Since the first human case in Nevada was identified in 2005, 210 people have been infected. Three have died.