Members of the U.S. military set out 10 traps near the Potomac River in Montgomery County last night to catch mosquitoes and determine whether they could transmit malaria.
The mosquitoes will be examined today to see if they are the anopheles species that carry malaria parasites.
There is no doubt there are anopholes mosquitoes in the county, health officials said. The question is whether they are carrying malaria.
“To our knowledge, we have had no locally contracted malaria,” said Dr. Carol Garvey, the county’s health officer.
Typically, 35 to 55 county residents are stricken with malaria every year, Dr. Garvey said, but “in every case it has been in persons who have traveled abroad.”
Montgomery has begun catching mosquitoes since malaria-carrying mosquitoes were found across the Potomac River in Loudoun County, Va., where a 15-year-old boy and 19-year-old girl were diagnosed with the disease three weeks ago.
Neither teen-ager had been out of the country, nor in contact with foreign travelers. Clarke Mosquito Control of Herndon went trapping and found female anopheles mosquitoes with the malaria parasite in Loudoun County.
“The areas where we found anopheles were very close to Montgomery County,” said Dr. David Goodfriend, director of the Loudoun County Health Department.
Montgomery County and Maryland asked the Uniform Services University of Health Sciences in Bethesda to set mosquito traps, generally in the Poolesville area. After testing the mosquitoes, Uniform Services made up of members of the military reports the results to the state’s Department of Health, which provides results to counties.
This was the first time Montgomery County had asked Uniform Services for assistance. Dr. Garvey said the county and Uniform Services work closely together.
“We train some of them who are interested in medical programs,” she said.
Washington-area health organizations have been scrutinizing mosquitoes this year because of an outbreak of West Nile virus, carried by another species of mosquito. West Nile has killed 108 persons in 32 states and the District this year.
Malaria, which is transmitted by parasites the mosquito injects into the bloodstream, is not so deadly in the United States but kills nearly 3 million each year worldwide. Clarke Mosquito Control in Herndon has been trapping and testing mosquitoes in Loudoun and Fairfax counties, Alexandria and Leesburg since the two teenagers were diagnosed.
“We set out 90 traps a week, at night,” said entomologist John Neely, mid-Atlantic operations manager for Clarke. “It is important work. We try to control them with larvacide before they become biting adults.”
Mr. Neely said two types of traps are used.
The ABC trap consists of dry ice, a dim light and a fan that sucks the blood-seeking mosquitoes into a net. This is the trap being used in Montgomery County, as demonstrated yesterday by Don Roberts, entomologist professor of Uniform Services.
“[The mosquitoes] will be eradicated by the first freeze,” Mr. Roberts said. “The reason we are doing this is to make sure there is no risk.”
The Gravid Trap similarly catches mosquitoes, but when they are looking for a place to lay their eggs.
Every morning, workers bring the live mosquitoes into a laboratory where they are sedated and examined for diseases. An antigen reactor finds West Nile virus. Another test examines the mosquitoes’ proteins for signs of the malaria parasite.
“We have to be very thorough,” Mr. Neely said. “So far, we have identified 28 species.”
When parasites are found, Clarke workers take larvacide to the pools where the carrier mosquitoes were caught to kill mosquito eggs and babies. The larvacide is effective for about a month.
And with cooler weather coming, the mosquitoes will probably pose little danger.
It’s very likely that this outbreak is over,” Mr. Roberts said.