With the number of area cases rising, McHenry County residents should do their part to help prevent the spread of West Nile virus.

An early and unusually warm spring contributed to larger populations of disease-carrying mosquitoes this summer. Mosquitoes can contract the virus by biting an infected bird, then pass it on by biting a human.

To date, McHenry County has had no confirmed cases of human West Nile this year. But 21 of the 190 mosquito batches tested in McHenry County have tested positive for the virus, and four birds have tested positive.