Efforts to battle mosquitoes carrying West Nile virus in Pennsylvania continue this week as the Bucks County Department of Health plans to spray multiple areas in Lower Makefield Township.

Mosquitos with West Nile Virus have spread to more than half the counties in Pennsylvania, the state’s Department of Environmental Protection said. The virus spreads through mosquito bites, primarily to birds such as crows but also to humans.

The disease causes serious illnesses in about 1 in 150 infected people, and can prove fatal. No human cases have been reported in Pennsylvania or New Jersey this year.