The number of West Nile virus cases in people typically appear in late summer, when the mosquitoes that carry the virus turn to humans after their preferred meal tickets, birds, head to warmer climates for the winter.
Tomato and cucumber plants aren’t the only seasonal staples benefiting from the longest streak of soggy summer weather in decades.
The mosquitoes behind the sometimes deadly West Nile virus are thriving, with both Pennsylvania and New Jersey anticipating they’ll hit new record highs for positive West Nile Virus mosquito samples last set in 2012, health and environmental officials said. Already, Pennsylvania has nearly surpassed last year’s number of confirmed human infections of the seasonal virus.
The region is only halfway through the peak of West Nile virus season, and already 2,100 positive mosquito samples have been recorded in Pennsylvania, according to Neil Shader, spokesman for the state Department of Environmental Protection. Last year the state had 2,500 positive samples total for the year, he said. Positive samples have been reported in 57 of the state’s 67 counties, up from 49 counties last year.
Every New Jersey county has reported positive West Nile virus mosquito sample pools, with a record number of 111 pools reported the week of Aug. 20. As of mid-August, three elderly state residents have tested positive for West Nile virus and required hospital treatment; last year eight people were diagnosed with the illness.
The higher-than-usual counts for West Nile virus-infected mosquitoes this year means the risk for human infection will likely remain elevated over the next few months, according to a press release from the Montgomery County Office of Public Health.
Health officials there announced Thursday they were investigating two probable cases of West Nile in a 59-year-old Montgomery Township resident and a 66-year-old Lower Merion resident. Bucks County also has confirmed two human cases of the virus, though the county health department did not release information on the age and locations of the victims. Both counties last had confirmed human West Nile infections in 2016.
Statewide, at least 18 confirmed West Nile cases have been confirmed in humans so far this year, according to the Pennsylvania Department of Health. Last year, the first West Nile positive in an individual was reported in August and overall 20 people tested positive, according to health agency spokesman Nate Wardle. No deaths have been reported this year, Wardle added.
Since 2008, 183 Pennsylvania residents have tested positive for West Nile; 33 have died, according to state data.
The frequent stretch of heavy rain and flooding has resulted in the wettest summer in more than two decades, creating the ideal breeding ground for the Culex species of mosquito that carries the virus and can transmit it to animals, birds and humans. High humidity on top of the rain lets mosquitoes live longer so they can potentially spread the disease longer, officials said.
“The wet weather has been a culprit,” Shader said. “Even something as small as a bottle cap can be a breeding ground for mosquitoes. Even a rumpled tarp can hold enough water for mosquitoes to lay eggs in.”
Infected mosquitoes generally pose no serious health threat since most people do not get sick, health officials said. West Nile symptoms in people are similar to the flu, but it can lead to more severe symptoms such as brain swelling. People with weakened immune systems are most susceptible to severe illness, according to the Centers for Disease Control and Prevention in Atlanta.
Similar spikes in West Nile virus have been reported across the U.S. this month, according to the CDC. Forty-five states and the District of Columbia have reported West Nile in people, animals and mosquitoes, according to the federal agency. More than 100 cases have been diagnosed in people and four deaths reported.
Locally, Burlington County so far has reported 15 positive mosquito pools compared to 13 at the same time last year, according to state health data. Statewide, 284 mosquito pools in 20 Garden State counties have tested positive as of mid-August, compared with 192 for all last year, according to the state.
Southeastern Pennsylvania, which includes Bucks and Montgomery counties, has recorded the highest number of positive West Nile samples in the state so far, according to state data. Neither Bucks nor Montgomery counties are reporting positive tests in humans or animals, but the counties are reporting 118 and 107 positive mosquito samples, respectively.
Last year Bucks reported 162 positive mosquito samples and none in animals or humans; Montgomery County had one person infected and 124 in mosquito samples in 2017.
Bucks County is seeing a record high number of positive mosquitoes, said Phil Smith, who oversees the Bucks County Department of Health’s West Nile Virus program. The county’s three technicians check and set 45 traps a day in rotating communities throughout the county to monitor the situation, Smith said.
“It’s just off the charts. You can probably set a mosquito trap anywhere in the county and get positive mosquitoes,” he added. “This is without question the worst year.”
As birds — the preferred meal for Cutex mosquitoes — start heading to warmer climates in the late summer, mosquitoes turn to people for meals, which is why human cases typically start appearing in the latter part of the season, Smith said. West Nile is most commonly seen in July through September but can exist until the first hard frost.
To prevent the spread of the virus, Bucks County is spraying areas with high positive samples every other night, rather than two or three times a week, Smith said. By the end of August, the county anticipated eclipsing the 15 adult sprays the county did last year, spokeswoman Juliet Kelchner added.
Bucks County is using a $144,283 DEP grant to cover the cost of its West Nile virus control sprays this year, but it’s too soon to know if the money will last the season, Kelchner said. Bucks is one of 30 counties that the DEP funds for West Nile control.
So far, DEP’s Shader said that his department hasn’t heard from any counties with concerns the funding will run out before the season is over.
Montgomery County officials said they are continuing to target areas with pesticide spraying where adult mosquitoes pose a risk of human infection, but due to “extensive and widespread” detection of the disease-carrying mosquitoes some areas may not be treated.