The first Idaho mosquitoes to test positive for the virus in 2012 prompted health officials to remind people to take precautions.
The mosquitoes were found in a trap near the Expo Idaho fairgrounds in Garden City.
The virus is showing up a little earlier this year than in 2011, when Idaho didnt see signs of it until August.
In 2006, Idaho led the nation in West Nile illnesses with almost 1,000 infections, which contributed to 23 deaths. Last year, three people in Idaho were reported with West Nile virus.
Conditions are favorable for mosquitoes right now throughout the state; it is important that everyone protect themselves from biting mosquitoes, said Dr. Leslie Tengelsen, deputy state epidemiologist with the Idaho Department of Health and Welfare.
West Nile virus is usually contracted from the bite of an infected mosquito; it is not spread from person-to-person through casual contact. Symptoms of infection often include fever, headache, body aches, nausea, vomiting, and sometimes swollen lymph glands or a skin rash on the chest, stomach, and back. In some cases the virus can cause severe illness, especially in people over the age of 50.