EEE threat waning, trackers eye new mosquito-borne threat
By Kay Lazar
Globe Staff / May 18, 2008
Four years after Eastern equine encephalitis was first detected in Essex County, the region's top mosquito tracker is confident the latest outbreak of the potentially deadly virus, which spikes about every 15 years, is waning. But a new bug-borne threat - posed by the Asian tiger mosquito - may be on the doorstep.
Asian tigers are aggressive biters that have caused widespread misery in Asia and Africa and are migrating north from the southern part of the United States, bug specialists say. Last summer, six mosquitoes believed to be Asian tigers were caught in traps in Essex County, but a positive identification wasn't possible because the insects were too badly damaged, said Walter Montgomery, director of the Northeast Massachusetts Mosquito Control and Wetlands Management District. The agency tracks and kills mosquitoes in 33 communities north of Boston.
Asian tigers spread a debilitating joint disease, known as Chikungunya fever, among other viruses.
While the illness has not been diagnosed in this country, health authorities are concerned because Asian tigers are increasingly showing up in Northern states such as Ohio. And Chikungunya spread last summer from Asia and Africa to Italy - the first known outbreak outside the tropics. That demonstrated the bug's ability to survive and transmit disease in colder climates.
"When these things float around in Third World countries, for the most part people here don't pay attention to them. People are paying attention to Chikungunya now," Montgomery said.
His agency will soon deploy six traps throughout Essex County designed to lure Asian tigers, to confirm whether the insects are here and measure their concentrations. Except for six caught in 2000 in New Bedford, the insects have not been detected anywhere else in the state.
The state's chief disease tracker, Dr. Alfred DeMaria, said Asian tigers are "just getting on the radar" of public health authorities here, but what officials do know so far is troubling.
"They will bite anything with blood. They are not fussy eaters," DeMaria said. "Where Chikungunya has occurred in other places, it's been very problematic."
Chikungunya is rarely fatal, but it is more easily spread than West Nile virus and Eastern equine encephalitis, diseases that also are relatively rare in Massachusetts. West Nile and EEE are spread by mosquitoes that have bitten infected birds, but Chikungunya transmission is not reliant on birds - the disease is spread directly from bugs to humans.
While West Nile has become endemic in the region, health authorities did not detect any mosquitoes with EEE last year in Essex County, leading them to believe the concentration of virus is declining after a steady buildup since 2004. There were, however, several EEE-infected mosquito pools and three human cases last year in southern New Hampshire.
Health authorities say Asian tigers are particularly hardy insects that multiply quickly, and infestations are extremely difficult to control, in part because the mosquitoes attack day and night.
"Adulticide sprays aren't very successful against these mosquitoes," said Joe Conlon, a bug specialist and technical adviser to the American Mosquito Control Association. "Asian tigers can hide well during the day; they hang upside down at the tops of walls and sprays don't get to them. They hide under gardens in myrtle ground cover."
Asian tigers breed in small amounts of fresh water, such as puddles on tarps that cover wood piles or in rainwater in tire piles.
Authorities don't think the insects have spread diseases to people in this country, but they have isolated the West Nile virus and St. Louis encephalitis in Asian tigers here, Conlon said.
After conferring with mosquito control officials in New Jersey - where Asian tiger populations appear to be growing quickly - the chief tracker along the Bay State's southern border is boosting surveillance with a lot more traps in the region that includes Fairhaven, Fall River, and New Bedford. The six Asian tigers found in 2000 were near a tire recycling center in New Bedford. "It was such a fluke," said Wayne Andrews, mosquito control superintendent in Bristol County. "We went back in 2001 and 2002, and they seemed to die out in the winter, but they could very well" come into the country in imported tires.
"The question is: Do they get established? Do they make it through the winter? And that's the question we need to answer."
Montgomery, Essex County's top tracker, declined to say where his agency found the suspected Asian tigers last year, saying he didn't want to alarm residents.
While local authorities are on a steep learning curve with Asian tigers and Chikungunya, DeMaria, the state's top disease monitor, said the public should wear bug repellent and take other precautions, but also remember to keep bug-borne diseases in perspective.
"All of these diseases," DeMaria said, "are dwarfed by influenza."
Kay Lazar can be reached at firstname.lastname@example.org.