The Washoe County Health District Vector-Borne Disease Program confirms that mosquito samples from Hidden Valley and Rosewood Lake tested positive for West Nile Virus . No human cases have been reported in Washoe County so far. WNV is most commonly spread through the bite of infected mosquitoes. Take steps to avoiud bites. The Health District is increasing mosquito surveillance and will conduct early-morning insecticide fogging today, in the area of Hidden Valley and Rosewood Lakes.