Cases of West Nile virus in mosquitoes on the rise

The first case was reported in early April. Last year, that didn't happen until late June. West Nile has already been detected in Contra Costa, Solano and Santa Clara counties.

Vector control experts say a warm, wet spring created ideal conditions for mosquitoes to thrive and reproduce. Mosquito control efforts are also being hampered by new federal pesticide rules.

Copyright © 2019 KGO-TV. All Rights Reserved.