Warren County reports high West Nile virus activity after 4 more mosquito samples test positive
WARREN COUNTY, N.J. — Four additional mosquito samples collected in Warren County have tested positive for West Nile virus, bringing the county’s total to 33 positive samples this year, according to the Warren County Mosquito Control Commission.
The latest positive samples consisted of mixed Culex mosquitoes collected from gravid traps Sept. 9 in Allamuchy, Blairstown, Hackettstown and Hardwick Township.
So far this year, 33 of 335 mosquito samples tested in Warren County have been positive for West Nile virus. Each sample can contain up to 75 adult mosquitoes of the same species collected from a single location.
The commission said Warren County averaged about 11 West Nile virus-positive mosquito samples annually between 1999 and 2025.
Positive samples have been found in communities across the county this year. Lopatcong Township has recorded five positive samples, followed by Washington Township with four. Belvidere and Franklin Township have each recorded three.
Frelinghuysen Township, Greenwich Township, Hackettstown, Liberty Township and Mansfield Township have each recorded two positive samples.
One positive sample has been recorded in Allamuchy, Blairstown, Hardwick Township, Harmony Township, Hope Township, Knowlton Township, Oxford and Phillipsburg.
For West Nile virus surveillance, adult mosquitoes are collected from traps specifically designed to catch Culex mosquitoes, which are responsible for transmitting the virus, particularly from bird to bird.
The Warren County Mosquito Control Commission has been collecting and submitting mosquito samples for testing each week since the state laboratory began mosquito testing for the year May 18.
According to the commission, four people have been confirmed positive for West Nile virus in New Jersey so far this year, and there have been two presumptive viremic blood donors. Mid-to-late August is typically the peak period for humans and other mammals to acquire the virus.
Mosquito populations are currently very high in parts of Warren County following recent rainfall, according to the commission.
Commission staff conduct mosquito larval control throughout the county daily. Treatments to reduce adult mosquito populations in areas where West Nile virus-positive mosquitoes have been detected are conducted as weather permits.
Residents are urged to eliminate standing water around their properties, use mosquito repellents containing DEET, picaridin or oil of lemon eucalyptus and avoid being outdoors when mosquitoes are most active, typically around dawn and dusk.
The commission also asks residents to report neglected swimming pools by calling 908-453-3585 or visiting WarrenCountyMosquito.org. Reports can be made anonymously. The commission said one neglected swimming pool can produce more than 1 million mosquitoes and affect people up to five miles away.
Symptoms of a mild West Nile virus infection can include fever, headache, tiredness, body aches and swollen lymph glands. The commission said illness can last from a few days to several weeks.
Less than 1% of people infected with West Nile virus — about 1 in 150 — develop severe illness. Severe symptoms can include high fever, headache, neck stiffness, disorientation, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis. West Nile virus infection can be fatal.
Warren County recorded two severe human cases of West Nile virus in 2024.
