With New Jersey’s West Nile virus season peaking in the next month, the state’s county labs have been collecting and studying mosquitoes and their spread of the virus. And many are predicting this year to be an active season.

One such lab is Bergen County’s mosquito-fighting program, which sees the prevalence in its surveillance traps called “pools” to track the bugs. Some of the pools are baited with fermented water and grass, said Matt Bickerton, the county entomologist.

“So it has a certain type of odor, we call it ‘stink water,'” he explained.

It turns out the stink water is irresistible to Culex mosquitoes, making it easy to trap and check them for West Nile virus. Another trap uses the smell of human sweat to lure Asian Tiger mosquitoes, another West Nile vector.

And so far, lab tests of these so-called mosquito “pool” samples reveal a potential problem, Bickerton said.

“In the last couple weeks, almost all the mosquitoes we tested were positive for West Nile,” he said. “It’s above average. It’s kind of in line with last year, when quite a few people got sick from West Nile virus.”

Pool traps get tested weekly across the state. Out of more than 5,333 mosquito pools tested in New Jersey so far, 384 so far this season have revealed positive evidence of West Nile virus, covering 19 of 21 counties, officials said.

Mosquitoes like warm, wet weather, and they breed in standing water in amounts as small as a bottle cap.

“This is a hot zone,” Bickerton said. “Bergen County, Hudson County, Union County tend to be relatively high for West Nile. “We think that’s maybe because the mosquitoes that are the best vectors for West Nile virus are urban, the urban species.”

Mosquito larvae mature in about a week, and females live for maybe a month, laying multiple egg batches.

Bergen County’s attack plan targets newly-hatched larvae, called “wrigglers.” The $2 million “Bergen Bites Back” program sprays residential neighborhoods with Vectobac — a biological larvicide — usually over housetops and into yards during the pre-dawn hours.

“You’ve got to be proactive in some fashion,” said Mary Amoroso, chair of the Bergen County Board of Commissioners. “So I think part of it is an education process, explaining to folks the trade-offs. And we are using the safest products on the market.”

Bergen County residents can also call the county and ask to have their yards individually sprayed for free. Residents are urged to clean pools, and dump standing water, even birdbaths. In addition, the county deploys special minnows that devour the larvae in ponds and lakes.

Meanwhile, global warming only helps extend the Culex mosquito’s breeding season, Bickerton said. “We had an early West Nile positive — May 21 — that was very unusual,” he said. “We haven’t had activity that early in recent memory,”

Last year, New Jersey reported 41 human cases of West Nile in 14 counties, with eight deaths from complications. That compared to 13 cases and one death across seven counties in 2023.

“More people probably who get infected with West Nile have no symptoms,” Bickerton said. “The issue is that for certain people — especially immune-compromised and elderly — it can be fatal.”

Mosquitoes carry other diseases too, including dengue fever, malaria and chikungunya.