The Southern Nevada Health District has its first confirmed West Nile virus-positive mosquitoes of the season, and its first human case. A woman in her 50s suffered the more serious form of the illness. She was stricken in April and has recovered. The West Nile virus-positive mosquitoes were found in the Boulder City area. There were no reported human cases of West Nile virus in Clark County last year.  Dr. Joe Iser, chief health officer for the Southern Nevada Health District encourages everyone to take the appropriate precautions to do their part to ensure their homes are free of standing water, use insect repellent appropriately and report mosquito activity. West Nile virus is most commonly spread through the bites of infected mosquitoes that have acquired the virus by feeding on infected birds.