By Yiqing Wang/WHRO

West Nile virus is showing up in Virginia Beach mosquitoes at a level the city’s biologist says she has not seen in four years.

Virginia has reported six human cases so far this year, including one in the Eastern Region, though Virginia Beach officials said Aug. 19 that no human cases had been reported in the city.

But the city has detected the virus in 50 mosquito pools collected from 24 locations this season. In each of the previous two or three seasons, only one or two pools tested positive.

“This is a high year for us,” said Kaitlyn Price, a mosquito biologist with the Virginia Beach Public Works Mosquito Control program. “I don’t think that I have tested this many mosquitoes at this point in the season in my four years of being here.”

A mosquito pool is a group of mosquitoes collected from the same trap and tested together. Price said some traps caught so many Culex mosquitoes, the main carrier of West Nile virus, that the mosquitoes had to be divided into several pools.

Despite the sharp increase in positive mosquito pools, Price said the results do not mean human cases will rise at the same rate.

“We’ve had years where we’ve had way more mosquitoes and no disease activity,” Price said.

Mosquito populations can rise or fall with temperature, rainfall and the availability of standing water.

Most people infected with West Nile virus do not develop symptoms. Some experience fever, body aches, vomiting, diarrhea or a rash.

Rare cases can cause severe neurological illness or death, with older adults and people with weakened immune systems facing greater risk.

Price said Virginia Beach places about 90 mosquito traps across the city each week. Workers collect the traps, identify the mosquito species and test pools of species known to carry disease.

This year, the city has tested more than 300 pools for West Nile virus and Eastern equine encephalitis, another viral disease spread by the bites of infected mosquitoes.

When a pool tests positive, crews increase surveillance and apply larvicide to standing water in the surrounding area. The treatment kills mosquitoes before they develop into flying, biting adults.

“It’s much more effective to control mosquitoes while they’re in the larval stage because they spend three quarters of their life there versus when they’re adults and actively flying and biting,” Price said.

Price said the city also uses nighttime spraying when monitoring shows high mosquito numbers or continued virus activity.

The Virginia Beach Department of Public Health is notifying residents and explaining how they can reduce their exposure, said Rob Robinson, the department’s environmental health program manager.

Robinson urged residents to empty water from flowerpots, birdbaths, clogged gutters, children’s toys and other containers that can become breeding sites. He also recommended using insect repellent and wearing long sleeves and pants between dusk and dawn.

“The best preventive measure to avoid the virus is to avoid being bitten in the first place,” Robinson said.