Independent contractor Clarke Environmental Mosquito Control has been trapping and testing mosquitoes throughout Fairfax County since July looking for evidence of the West Nile virus. On Sept. 9, the county expanded Clarke's duties and asked the company to also test the collected mosquitoes for malaria, given that two teen-agers in Loudoun County had tested positive for the disease.
Last Tuesday, Oct. 1, four mosquitoes trapped near Mustang Drive, outside of the Town of Herndon, tested positive for malaria. So far, there have not been any reports of county residents contracting malaria without first having traveled overseas.
"It is not common to see cases contracted locally, but it is not unheard of," said Happy Callaway, a nurse in the Fairfax County Health Department's communicable diseases program. "In the last 30 years, I think there have been something like 80 cases where people have developed malaria without international travel."
Before the two Loudoun cases in September, the last reported locally contracted case of malaria in Virginia was in 1998 in the Tidewater area. In 2000, there were 23 reported cases of malaria in Fairfax County, and all were linked to international travel.
THE LACK of additional reported cases that cannot be linked to international travel has cast some doubt on the results of the testing, which destroys the mosquito, making retesting impossible.
The Virginia Department of Health has asked Clarke to forward all Anopheles mosquitoes, the type that carry the malaria parasite, to the state laboratory for testing. In addition, the state agency sent its own personnel to the Mustang Drive area to collect mosquitoes.
"There is a question about the number of positive tests in the area with no reports of human cases since the two teen-agers. If the results are wrong, it's good news," said Dr. Suzanne Jenkins, assistant state epidemiologist. "Lab tests are not infallible. If someone got test results back that said they had a raging infection but they felt fine, they should be retested. We have tests telling us we have an epidemic, without the epidemic."
In all, Clarke technicians have reported three mosquito pools have tested positive in Fairfax and Loudoun counties.
Fairfax County is not taking any chances. Merni Fitzgerald, the county's director of public affairs, said Fairfax has already started larviciding the area within a 1-mile radius of the reported positive mosquito pool.
"We are not spraying. We're taking naturally occurring bacteria in tea-bag-like things and tossing them in the water. And we're putting drops of oil in the water," Fitzgerald said. "The bacteria explodes in the stomachs of the mosquitoes, and the oil puts a thin sheen on the mosquitoes and they can't get out of the water."
The report on Oct. 8 that the Montgomery County Health Department is confirming mosquitoes trapped on the Maryland side of the Potomac River, near Loudoun County, tested positive for malaria has not altered the county's plan of attack, said Fitzgerald.
"It has no affect on us," she said. "We had already made the decision to do trapping and testing in an area in the proximity to Loudoun. We have already made the decision to larvicide."
The county had requested the Mustang Drive-area mosquito pool be tested because of its proximity to the Loudoun County border and because it's a low-lying area with the Horsepen Run traversing it, Fitzgerald said, making it a breeding area for mosquitoes.
It is not known, however, where the mosquitoes may have contracted the malaria parasite. The Anopheles mosquito does not migrate and tends to stay within a 1-mile radius of its breeding ground. Mustang Drive is about four to five miles from the Loudoun County border, Fitzgerald said.
The health experts said there are a few possibilities as to how the mosquitoes came to carry the parasite. It is possible someone traveled overseas to an area were malaria is epidemic, contracted the disease — which can lie dormant — and when he returned was bitten by a local mosquito, which then carried it to another person. It is also a remote possibility the mosquitoes came to the area by way of an international flight that landed at Dulles International Airport.
MALARIA is a parasite that gets into a person's bloodstream. There are four types of malaria, with the most serious being plasmodium falciparum, which can be fatal, said Callaway. The type contracted by the Loudoun County teens was plasmodium vivax, a mild form of the disease.
Callaway said the parasite settles in the liver and becomes dormant, then it re-animates again.
"People may go a lifetime without having been diagnosed," Callaway said. "On a slightly brighter note, if you can call it that, once people have been affected, they have a certain amount of resistance to it."
She said all four forms of malaria are treatable with medications and are preventable if someone who is traveling to a malaria-infected area begins taking medications before and after the trip, as prescribed by their doctor.
All forms of malaria cause high fevers and chills that tend to be relapsing or come in cycles. The disease also causes body aches, vomiting and headaches.
Since many viral infections tend to produce the same flu-like symptoms, Callaway said, people should seek medical attention if the symptoms persist for more than five days.
"Six months ago, a person probably wouldn't have been tested for this," Callaway said. "[On Wednesday,] we sent out a fax to physicians to be aware that malaria is a possibility."
Even so, Jenkins said, should further testing confirm Clarke's findings, it is not a health crisis.
"I'm much more concerned by West Nile virus right now," Jenkins said. "The potential to be infected by West Nile virus is much greater.
“Malaria is an unusual event. It is not very often do we get people in the U.S. affected in the U.S."