Officials testing mosquitoes after 2 malaria cases in Va.

Loudoun County teens were stricken in August

October 02, 2002|By Dennis O'Brien | Dennis O'Brien,SUN STAFF

POOLESVILLE -- For the first time in at least 20 years, state health officials began collecting mosquitoes to test them for malaria last night, placing traps along the shores of the Potomac River to see if the deadly parasite has migrated from Virginia into Maryland.

Military researchers from the Bethesda-based Uniformed Services University of the Health Sciences placed box-like traps in marshy soils along the Potomac just a few miles north of where two teen-agers from the suburbs of Loudoun County, Va., contracted malaria in August. It also was detected near two Virginia ponds where malaria-infected mosquitoes were found last week.

The eight researchers met off Edwards Ferry Road near Poolesville, divided into groups of two and walked along a back road near the edge of the Potomac. They hung mosquito light traps that they hope will capture enough mosquitoes to determine if malaria has come to Maryland.

"You want to hang them in a place where the mosquitoes are going to get a good view," said Phillip Lawyer, a medical entomologist, as he placed one trap along a stream beside the road.

Dr. David Goodfriend, Loudoun County's health director, said the two Virginia teen-agers likely were infected in mid-August from mosquitoes at a pond close to their Sterling, Va., homes, which is a gathering place for anopheles quadrimaculatus, the type of mosquitoes known to carry malaria.

No vaccines exist for malaria, a parasite that is transmitted mostly by mosquito from the blood of one human to another.

Although the disease is a scourge overseas, infecting 500 million each year and killing a million, the strain of malaria that infected the two Virginia teen-agers is believed to be a milder form.

Loudoun County officials have requested help from the Centers for Disease Control and Prevention in Atlanta, where researchers are conducting genetic tests on the teen-agers' blood and on the mosquitoes found in the two ponds to try to determine the origin of the infection.

Goodfriend and other health officials said tests conducted by CDC also may help determine if the two malaria cases and the mosquitoes were all infected with blood taken by a mosquito from the same individual.

Goodfriend said malaria was diagnosed in a 15-year-old boy in mid-August after he showed up at Loudoun County Hospital with a high fever. A 19-year-old girl was found to have the disease after she went to her doctor with fever and chills; her blood was tested for malaria when the symptoms persisted despite treatment with antibiotics, Goodfriend said.

Goodfriend said yesterday that both teen-agers have recovered and are doing well.

Medical experts say that the Virginia cases are a rarity because they originated in the United States.

Although 1,200 cases of malaria are reported in the United States each year, almost all of the victims are infected while overseas.

There may be one or two cases each year that originate in the United States, experts said, but it is extremely rare for malaria to be traced to nearby pools of mosquitoes.

"They've never found infected pools like this before," said Dr. David Sullivan, a physician with the Malaria Research Institute of the Johns Hopkins Bloomberg School of Public Health.

Cy Lesser, chief of the Maryland Department of Agriculture's mosquito control program, said malaria was nearly wiped out in the United States in the 1950s and it has been at least 20 years since the state collected mosquitoes to test them for malaria.

He and other experts said that the mosquito-borne West Nile virus remains a more serious health threat in Maryland than malaria.

"There are several species of mosquitoes that will transmit West Nile. But in the Eastern U.S., there's only one mosquito that will spread malaria," Lesser said.

Loudoun County had been collecting mosquitoes to track the West Nile virus all summer, he said. When the disease was diagnosed, county officials began testing mosquitoes for malaria as well, he said.

Mosquitoes taken from a pond near a retirement community, about 6 miles west of where the teen-agers live, tested positive for malaria Sept. 25. Another pool of mosquitoes collected about 4 miles away tested positive Friday.

Both pools of mosquitoes proved to have the same type of malaria parasite -- there are four -- that infected the teen-agers, he said. It is known as plasmodium vivax and is considered less lethal than the variety responsible for the estimated 1 million deaths worldwide each year, Goodfriend said.

He said that because mosquitoes can travel only about a half-mile, the teen-agers are more likely to have contracted the disease from a pond near their homes than from either of the two ponds where the infected mosquitoes were later found.

The traps used by entomologists trying to track mosquitoes look a little like Japanese lanterns. Near the top is a tear-drop-sized light to attract mosquitoes.

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