The infected insects have been found at seven spots around the county, including in Caldwell, Middleton, Notus, and Parma.
Recent triple-digit temperatures have resulted in a spike in mosquito populations, according the Canyon County Mosquito Abatement District. The group has been trapping the insects to test for West Nile Virus since early May.
Crews are ground-treating areas where mosquito larvae have been found, and spraying in low volumes at night to kill the flying adults.
West Nile Virus is a potentially life-threatening illness. While most people who contract the illness have no symptoms, one in five will experience fever and flu-like symptoms, according to the Center For Disease Control. In rare cases, victims suffer neurological symptoms that can be fatal.
The Canyon County Mosquito Abatement District urged area residents to protect themselves against the disease. The group warned to avoid mosquitoes at night, as the species that carries the virus is most active between dusk and dawn.
Draining any standing water around homes, using insect repellant, covering exposed skin, and insect-proofing houses can also help reduce chances of an infected bite.