Fever fight

Ideal conditions for West Nile virus-carrying mosquitoes provoke campaign to wipe them out

Email|Print|Single Page| Text size + By Ralph Ranalli
Globe Staff / August 7, 2008

NEWTON - With his white baseball cap flipped backward and his T-shirt flapping as he pumped his Gary Fisher cruiser bike up a hill on Commonwealth Avenue last week, Charles King looked more like a college student heading to a summer lifeguard job than the first line of defense against a potentially lethal pathogen.

Pulling up to a storm-drain cover, the 24-year-old stopped by the curb, reached into a blue nylon bag attached to the bike's wide handlebars and dropped a packet the size of a Tootsie Roll through the square grate and into the catch basin below. To show that the drain had been treated with Altosid - a brand of the larvicide methoprene, which mimics a mosquito growth-regulating hormone and prevents larvae from becoming winged adults - he marked the grate with a dot of fluorescent green paint from a spray can attached to a long metal handle.

One catch basin down, 9,999 more to go - in Newton alone. As King remounted his bike, three other young men on similar wheels were fanning out across city, where they would be treating catch basins in a similar fashion for the next 10 hours. In all, the crew is tasked with treating nearly 50,000 storm drains in cities and towns across the region.

Such is the puddle-by-puddle battle being waged against the Culex mosquito in what public health officials fear may be the worst summer in years for the West Nile virus in Boston's western suburbs.

Conditions for Culex and other mosquitoes that carry the West Nile virus are nearly ideal this year thanks to a number of factors, including a lack of severe cold weather last winter, large numbers of heavy rainstorms in the spring and early summer, and the region's dense population growth, East Middlesex Mosquito Control Project superintendent David Henley said last week.

Reports of infected mosquitoes and birds first surfaced in Brookline and Worcester in June - early in the season - and have steadily moved toward the center of the region, Henley said. During the last month, West Nile-carrying mosquitoes have been found in Watertown, Needham, and Millbury, while birds killed by the virus have turned up in Newton, Sudbury, and Framingham.

"There have actually been three prior years when mosquitoes have been found in June, and two of those years were peak years for West Nile virus, 2002 and 2003," Henley said last week at the Waltham headquarters of the state-funded control project. "I expect that by the second week of August, we'll be seeing tremendous populations" of infected insects.

To combat the threat, mosquito-control officials are employing a number of measures, including a cadre of bike-riding larvicide spreaders like King, trucks conducting early-evening spraying of airborne pesticide to kill adult mosquitoes, and an aggressive monitoring program that involves a network of hundreds of mosquito traps.

West Nile fever, a disease common in the Middle East, West Asia, and Africa, was first documented on the East Coast of the United States in 1999, and has since spread across much of the country. While viewed almost universally with alarm, West Nile fever is less of a problem locally than in warmer regions of the country, where mosquitoes typically survive year-round. In Massachusetts, the West Nile season lasts from June or July - when the cycle of infected mosquitoes biting birds and diseased birds infecting more mosquitoes reaches critical mass - to the first killing frost of autumn.

No human infections have been reported this year. But officials say that is probably due more to the difficulty in gauging West Nile transmission to humans, rather than a lack of bites by infected mosquitoes. Officials say there are probably hundreds, even thousands, of people in the area who were infected at some point but will never know it.

According to the US Centers for Disease Control, an estimated 80 percent of humans bitten by infected mosquitoes develop no symptoms. Of the 20 percent who do - commonly fever, headache, fatigue, aches, and rashes - most attribute them to some other cause and never seek treatment. There is no testing or monitoring system among healthcare providers.

"Very likely, in most cases of West Nile in people, they will feel lousy for a week or so and then forget all about it," said the superintendent of the Central Massachusetts Mosquito Control Project, Timothy Deschamps, whose district extends from Natick to Shrewsbury and beyond, although not every community along the way is covered by the program.

Like influenza, West Nile fever can be serious and potentially lethal to the elderly, children, and people with compromised immune systems. In rare cases, it can be fatal to healthy adults if it infects the central nervous system and becomes West Nile encephalitis or meningitis.

To combat the threat, the East Middlesex project's assistant superintendent, Mike Bryant, and senior field technician Chris Gagnon were driving the back streets of south Framingham one evening last week, using a compressor-powered spray gun to pump out a steady mist of sumithrin, a pesticide that kills airborne mosquitoes. Mounted on the back of a green pickup truck, the gun sounded like a small aircraft revving for takeoff.

Most residents, warned by the town's reverse 911 system, were inside by 8:30 p.m. with windows closed as Bryant and Gagnon passed. Sumithrin, also known by the brand name Anvil, is said to be relatively safe for mammals, but can cause coughing, rashes, and eye irritation. Most of the spraying by the control project, Bryant said, is in response to requests from residents in particularly bad areas and data from mosquito traps.

"It pretty much drifts with the wind, and if there is a flying mosquito out there, it will pretty much knock it down," Bryant said. "But it breaks down in sunlight."

Controlling the flying mosquito population is also important because, unlike many mosquito species, Culex females who carry the virus spend the winter hibernating in warm, protected spaces, such as basements and heated parking garages. So far this year, officials said, monitoring has shown a larger-than-usual number of Culex mosquitoes survived the winter.

As he checked a mosquito trap near tiny Dolan's Pond in Newton's Auburndale section last week, East Middlesex entomologist Douglas Bidlack sounded disappointed when he found only a few females inside. The reason, he said, was not a lack of mosquitoes, but recent heavy rains that raised the water level in the trap so high no more mosquitoes could get in.

To bait the traps, Bidlack steeps oak leaves in water until they ferment. The resulting "brew" as is placed in a pan underneath the trap. Culex females, attracted by water with high nutrient content for their larvae, attempt to lay eggs, but are sucked into the trap by a small electric fan.

While an abundance of rain can create mosquito habitat, Bidlack and Henley said, an overabundance of precipitation can destroy it. Frequent rains can dilute nutrient-rich catch basins so they are less attractive to egg-laying females, and wash developing larvae into the Charles River, where they become harmless fish food.

Triple threat

Why West Nile mosquitoes could have a record year

Dense development:

Unlike most mosquitoes, the West Nile-carrying species spend the winter hibernating in warm, humid places such as basements and sewers. More houses mean more of such sanctuaries, as well as storm-water catch basins and rain-filled containers.

Mild winter:

Without a long winter freeze, more infected mosquitoes survive until May. An early start to a season that does not end until the fall's first cold snap is much more likely to result in human infections.

Heavy rains:

This year's steady series of storms has left a large number of rain-filled catch basins, water-filled containers, and lingering puddles, the preferred egg-laying habitats for Culex females.

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