Methuen plans to spray the city for mosquitoes Thursday after West Nile virus was found in a mosquito trap there.
West Nile virus was discovered in mosquito pools taken from traps in Methuen, Andover, and Revere, the Massachusetts Department of Public Health reported on Friday.
In Revere, the finding was the second from the same trap, near Beach and Harris streets. The area was sprayed after the mosquito pools were collected, but before the report came in that the trap tested positive for the virus.
In all, there have been five positive findings for West Nile virus north of Boston this summer, including two in Revere (in the same location) and one in Malden. All of the positive findings came from mosquito pools.
There have been no reported human or animal cases, and no reports of Eastern equine encephalitis in the region. Both of the mosquito-borne viruses can lead to diseases that are potentially fatal to humans.
There was widespread spraying last week to knock down the spread of EEE after positive tests in mosquito pools in Southeastern Massachusetts.
There have been no reported findings of either West Nile virus or EEE in Southern New Hampshire, according to the New Hampshire Division of Public Health Services.
The Andover and Methuen findings were the first in Essex County this summer. Jack Card, director of the Northeast Massachusetts Mosquito Control and Wetlands Management District, which manages the mosquito population in 31 Essex County communities and in Revere and Winthrop, said the district had placed additional traps in both communities earlier in the year because of the large population of the culex pipiens and culex restuans mosquito types, both vectors of West Nile virus.
Last weekend the district placed additional traps in Methuen and Andover to get a sense of the range of the potential problem.
On Monday, Methuen Mayor Stephen Zanni confirmed that the town would spray this week. He said the district had previously treated catch basins as part of normal mosquito maintenance.
Meanwhile, Thomas Carbone, Andover’s director of public health, said the town would make further decisions based on the next round of results, as it also alerted the public about the finding.
“We want people to know it’s there and do what they can to protect themselves,” said Carbone.
Although there have been no known cases of West Nile virus in humans in Andover, positive findings from mosquito traps are not unusual. Carbone’s department conducts public education campaigns annually to warn residents to take precautions such as using mosquito repellant with DEET, wearing long sleeves and pants, being mindful of mosquitoes during the peak activity periods of dusk and dawn, and looking around their own backyards to eliminate standing water in artificial “containers” (such as gutters, bird baths, spare tires) where the culex species breed.
“We want people to take an extra look around,” Carbone said. “That can go a long way toward solving the mosquito problem and West Nile issues.”
The West Nile virus was previously found in mosquito pools in Malden on July 3 and Revere on July 11.
Public health directors Christopher Webb from Malden and Nicholas Catinazzo of Revere both said that public education is a key component of dealing with the threat, with warnings issued every summer about West Nile virus protection.
Revere’s Board of Health also had the district spray near the area where its positive sample was found, and also on the Revere border near where the Malden sample was found.
In Malden, meanwhile, the East Middlesex Mosquito Control Project treated the catch basins in the area where the sample was found. The project also planned to test traps from Malden, Medford, and Melrose this week, and new results were expected by Thursday.
Some communities resist spraying, and Card said every community has input into how the mosquitoes are managed.
“Everybody’s different in how they react and approach it,” Card said.
The hot, dry weather through late June and early July may indicate a higher-than-usual West Nile virus risk, said David Henley, superintendent for the East Middlesex Mosquito Control Project, which runs a comprehensive mosquito management plan in Malden and other Middlesex County communities.
Citing recent research, Henley said the hot weather “speeds up the culex mosquito cycle, where they go out, bite somebody, ingest the blood, and lay eggs and then start the process again. It also, they think, speeds up the development of the virus in both birds and mosquitoes. We’ve had a month of hot, dry weather, so it’s certainly trending toward West Nile virus, but last summer the month of July was hot and dry and then we went into a cool and rainy August and it changed the pattern. So the pattern can change fairly suddenly.”
Because of the warm winter and spring, the mosquito cycle started earlier this year.
“There’s a general feeling that the mosquito season is running two weeks ahead of schedule,” said Henley. Most cases of both diseases in humans tend to happen in August and September, he said.
“If we started getting human cases earlier, that would be cause for concern because we’d have a longer risk period,” he said.
Because the weather has dried out some of the shallow wetlands in Middlesex County, Henley said, he’s finding low numbers of the culiseta melanura, a mosquito species that carries EEE.
“For EEE, it appears that the risk is staying in Southeastern Massachusetts right now,” Henley said.