- The Washington Times - Friday, October 4, 2002

Health officials are considering the possibility that a parasite similar to the one that carries malaria caused false results among mosquitoes that tested positive for the disease in Northern Virginia, even as the state health department is collecting more mosquitoes for testing.

The VecTest conducted in Loudoun and Fairfax counties to determine the presence of the malaria parasite is more than 90 percent effective, said scientists from the federal Centers for Disease Control and Prevention (CDC) in Atlanta.

"We are talking about the accuracy being in the mid- to higher- 90s," said Robert Wirtz, chief of the CDC's entomology branch.

The state health department yesterday started setting traps to collect mosquitoes in Northern Virginia because the VecTest consumes most of the mosquito, leaving little behind for any other tests.

Health and mosquito-control officials who vouch for the test's accuracy said they are puzzled there are no human infections corresponding to the large numbers of mosquitoes that have tested positive for malaria.

John Neely, Mid-Atlantic manager for Clarke Mosquito Control, which has been setting traps in Northern Virginia and testing the mosquitoes using the VecTest, said there had not been a false-positive result during the 40,000 times the test was conducted in Walter Reed Army Hospital.

Mr. Neely's workers were out setting traps in Fairfax and Loudoun counties yesterday to collect more mosquitoes.

Mr. Neely also said some types of malaria have a long incubation period in humans. "The time lapse with the Vivax malaria, found in the mosquitoes, can be a year," he said.

However, health officials said the incubation period in most people would last a couple of weeks. Other jurisdictions, like Montgomery County, which will have results for mosquitoes it collected within a week, are using laboratory tests instead of the VecTests.

"The field testing being used in Virginia is a relatively new technology and with anthrax it has not been very useful," said Carol Garvey, health officer for Montgomery County.

Health officials in Maryland and the District have not reported any positive test results for malaria.

The mosquito population and the threat of malaria are expected to drop in winter because mosquitoes cannot survive cold weather. But if the VecTests are accurate, health officials say there is a chance a small number of adult mosquitoes could survive and emerge next year.

While most adult mosquitoes will not survive the winter, there is a chance that some adult female anopheles mosquitoes infected with the parasite could make it, said Cyrus Lesser, chief of the mosquito-control division of the Maryland Department of Agriculture.

"If a female anopheles mosquito finds herself in a well-protected area, she could survive into the next spring," said Mr. Lesser, adding there is a very small chance that could happen.

The anopheles mosquito transmits the malaria parasite among humans, and large populations of this type of mosquito exist in the Washington area, officials say.

This week, several infected mosquito pools were discovered in Fairfax and Loudoun counties. In Loudoun, two teenagers contracted malaria about a month ago, spurring health authorities to set up traps to check mosquitoes.

Most malaria cases in the region and across the country over the past few years have been seen in people who travel abroad to countries with a high malaria incidence. However, the teens in Loudoun County had never been abroad or come in contact with someone who had traveled abroad.

This is the first time in 20 years that mosquitoes in the county have tested positive. But officials say this could be because they had never thought of testing before, because malaria had been considered eradicated.

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