North Valley mosquito districts track West Nile virus as summer activity surgesAs mosquito season peaks in the North Valley, mosquito control districts in Merced and Madera counties are monitoring activity for West Nile virusAs mosquito season peaks in the North Valley, mosquito control districts in Merced and Madera counties are monitoring activity for West Nile virusAs mosquito season peaks in the North Valley, mosquito control districts in Merced and Madera counties are monitoring activity for West Nile virusAs mosquito season peaks in the North Valley, mosquito control districts in Merced and Madera counties are monitoring activity for West Nile virusMADERA COUNTY, Calif. (KFSN) -- As mosquito season peaks in the North Valley, mosquito control districts in Merced and Madera counties are monitoring activity and testing for West Nile virus, with officials reporting different trends in each county. Fourteen mosquito samples have tested positive for West Nile virus, and no human cases have been reported. Crews are also monitoring mosquito populations during what officials say is the busiest time of year for mosquito activity. "July, August, September is our peak season for mosquito activity," said Abraham Velazquez of Madera County Mosquito and Vector Control District. Through July, the Merced Abatement District predicts a moderate risk of human infection from the West Nile virus.