Human infections typically are reported two or more weeks after the virus shows up in mosquitoes, Lance Madigan, Utah County Health Department's spokesman, said.
Utah County was the latest county to find infected mosquitoes, and reported two positive tests one from a batch in the south county area near Springville and another from west Orem.
Madigan said residents in other parts of the county should also be wary. "Mosquitoes can fly a great distance, even up to 10 miles," he said.
Through the week ending Aug. 2, Box Elder County had four positive tests for West Nile virus in mosquitoes, and Uintah County had three. Salt Lake and Washington counties each had two positive West Nile virus tests, and Davis and Weber counties had one each.
Symptoms of the virus include headache, body aches, joint pains, vomiting, diarrhea and rash. But most people 70 percent to 80 percent, according to the Utah Health Department do not develop any symptoms when infected.
Madigan said personal vigilance is the key to preventing spread of the virus. His advice:
• Avoid outdoor activities, such as gardening, at dusk through dawn when mosquitoes are most active.
• If outside when mosquitoes are most active, cover up by wearing long-sleeved shirts, pants, shoes and socks.
• Use mosquito repellents with DEET. Follow product directions for children and for frequency of application.
• Eliminate standing water in tires or similar water-holding containers as these may serve as mosquito breeding sites. Change the water in birdbaths at least weekly.
More information is available the Utah County Health Department, www.UtahCountyHealth.org.