City and state officials are stepping up monitoring efforts this week after a sample of mosquitoes captured in Dorchester last week tested positive for West Nile Virus, a bug and bird-borne disease that can be deadly to humans.
The city’s Boston Public Health Commission alerted the public to the discovery last Friday. While officials stress that the risk of individual human cases of West Nile are relatively low, extra mosquito traps have been set throughout the neighborhood this week to further probe the extent of the problem. City officials refused to narrow down the geographic location of the infected bugs beyond the general “north” Dorchester area, but emphasized that the disease is highly mobile and that people throughout the region should take precautions.
Dr. Anita Barry, director of the Boston Public Health Commission’s Bureau on Infectious Disease, said that despite the low risk, her advice to people of all ages is simple: “It’s not a good idea to get bitten by a mosquito.”
“It’s true that many people who get WNV infection will have very mild illness or even no symptoms,” Barry said. “People who are a little older have a higher risk. I worry, too, about the other mosquito-borne illness: Eastern Equine Encephalitis (EEE). We haven’t had that in any pools in Boston to date, but it’s transmitted the exact same way.”
Doctors, hospitals, and laboratories are required under state law to report any diagnosis of WNV to the Boston Public Health Commission, Barry said. But often human cases of WNV are never reported to authorities because those stricken with the illness don’t recognize the symptoms.
“It’s certainly under-diagnosed because so many cases are mild,” Barry said.
In fact, the CDC reports that up to 80 percent of people infected with WNV won’t show any symptoms. More seriously ill people will notice symptoms that can include fever, body aches, nausea, vomiting, swollen lymph glands, or a skin rash.
Barry said that aerial spraying — like the bombardments earlier this month in southeastern Massachusetts that were deployed to combat EEE-infected bugs— has not been considered for Boston to date.
“Aerial spraying is helpful but its effects only last for a relatively short period of time,” Barry said. “We’d have to see a lot more disease before we’d consider that.”
Some localized “nuisance spraying” is conducted in Boston by the Suffolk County Mosquito Control Project. Bruce Landers, superintendent of the project, also supervises dozens of mosquito traps — including several in Dorchester. The Reporter observed Landers as he positioned one such device in a private yard in Lower Mills on Tuesday.
The trap itself resembles a gray fishing tackle box propped atop a black litter box. Inside the box is a small fan that sucks the insects into a container. Landers dumped about one gallon of a putrid-smelling solution — water, mixed with hay and milk, he says— into the black tray. The smelly concoction attracts the kind of mosquitoes that health officials dread the most: culex pipiens. Landers says this particular species of mosquito is like a rat: it likes to be around people and animals and will often be found inside homes, garages, and basements. The pipiens prefer to feast on the local bird population — which is why it can be a threat in the spread of WNV. The disease first arrived in Boston back in 2000 via a diseased bird that likely migrated from Central Park to Jamaica Plain that year, Landers says.
“That year the epicenter was right near Brookline High,” says Landers. “It seems to be a chronic problem along the Brookline-Newton border. Because the disease usually comes from the west, most of our trapping is there. When [we find it] in the east we have to put out more traps to see if there’s more than one spot.”
Landers set eight new traps on Monday and planned to locate another eight traps on Tuesday night, he said. His team would then retrieve the contents of the traps — and if a large enough sample of mosquitoes was found — they would be sent to the state laboratory in Jamaica Plain for testing. Results of the Lower Mills trap set on Tuesday afternoon would be available on Friday, he said, if there was a sufficient population captured. He said that he would only submit tubes containing at least 32 bugs. Active mosquito traps can snag hundreds of bugs in one night, Landers says, but he added that the dry weather has dulled the volume lately.
“I don’t think you’re going to have a large population here,” he said after he poured the barnyard-scented solution into the trap in Lower Mills. “I haven’t been bit once since I’ve been here and that’s nice. Sometimes I start pouring this stuff and watch them try to fly into the bottle. It’s that bad.”
This week, with a statewide drought still underway, Landers says that the numbers of mosquitoes captured has been low. “Last night the high was 44,” Landers said. “Right now there’s not a lot of places [for mosquitoes to breed]. They can use catch basins, there’s still water in many of them. But there’s not much water in people’s backyards or bird baths or tires leaning up against the house. That’s what mosquitoes really like.”
Landers and his team — along with a separate unit of workers from the city’s Inspectional Services Department— have already “treated” most catch basins in the city with solutions aimed at reducing the mosquito population. Landers uses two different treatments: one includes a bacteria that kills bugs outright for up to 70 days. The other is a growth hormone that keeps larvae from developing into the adult mosquitoes that bite birds and people.
“We’ve treated all the catch basins in Dorchester already,” Landers said Tuesday. “We’re almost done. We’re just finishing Southie up. Inspectional Services is doing six areas; they just finished up Roxbury and the South End. We’re doing our traditional areas, where we think they’ll attack from, but all you really need is for a bird to have the disease and fly into a spot that’s unusual.”
Update (Aug. 24): Bruce Landers reports that his team retrieved some 70 mosquitoes- most of them culex pipiens- from the trap in the Lower Mills. A test done that week found that none carried the West Nile Virus. However, city officials did report another "hit" for West Nile elsewhere in Dorchester in the same "north" traps that tested positive the week before, as well as in another pool in West Roxbury.