The first positive case of West Nile virus has shown up in Mercer County.

State officials on Thursday reported that a dead American crow in Stoneboro tested positive for West Nile.

The virus is a disease that infected mosquitoes can pass on to birds, animals and people.

The extensive rain and flooding this summer can be blamed for increasing mosquito breeding areas and more mosquitoes hatching than usual, the officials said. Mosquitoes lay eggs in standing water, where they hatch into larvae. Killing the larvae before mosquitoes become adults helps to prevent the problem.

Mosquito pools in Pine Township tested positive for West Nile last week.