Mosquitoes across the northern counties of New Jersey have tested positive for West Nile virus, according to health officials.

The mosquitoes were found in areas of Bergen, Morris and Passaic counties. No human cases have been reported.

Officials are now taking precautions to prevent the virus from spreading.

One way is to trap the insects in special traps designed to attract the species of mosquito known as culex pipiens, which is the type that carries the virus.

Passaic County Mosquito Control has also begun using mosquitofish to eat the larvae and is also spraying for adult mosquitoes.

Officials say that despite what some may think, these mosquitoes are often found in high density areas.

“It does pretty well in the urban areas of Passaic County, so the lower half of the county,” says Joseph Pezzillo with Passaic County Mosquito Control. “We tend to see West Nile virus activity, which we see every year in our mosquito populations."

Homeowners are being asked to get rid of all standing water around their properties by emptying out gutters, containers and buckets. Mosquitoes breed in standing water.

"Obviously we have our work cut out for us,” Pezzillo says. “But homeowners and residents in Passaic County need to know they play a big role in mosquito control as well."

Homeowners concerned about the virus should use insect repellants when outdoors, have their properties sprayed and clear their homes of standing water.