Locally acquired malaria could become common. (Cases Diagnosed in Suburban Washington).

Pockets of locally acquired cases of malaria could begin to spring up in the United States.

The resurgence of malaria in a Virginia suburb of Washington, D.C., might be the first instance of what could be an emerging problem in other areas of the country.

Malaria could threaten areas with the right combination of risk factors in place--a resident population of Anopheles quadrimaculatus mosquitoes and a large number of recent immigrants from developing countries or travelers to those countries where malaria is endemic.

Four populations of malaria-infected mosquitoes have been identified in the Virginia suburbs of Washington. The surprising finding has health officials wondering how many local residents could be harboring the malaria parasite.

The Washington suburbs are ethnically diverse, "with residents from dozens of different countries, most of which have malaria, as well as many people traveling back and forth between those areas. ... Obviously, there is some degree of asymptomatic malaria out there," which could be the source of the parasite in the infected mosquitoes, Dr. John Marr, who is an epidemiologist for the Virginia Department of Health, told this newspaper.

In asymptomatic people, malaria parasites can persist at low blood levels, providing a continued source of infection to mosquitoes.

"This is not a unique environment in Virginia. In fact, I would say it's becoming increasingly common," Dr. Marr said. "With so many people from developing countries [in] South and Central America, Asia, and Africa, I wouldn't be surprised to see additional cases of locally acquired malaria in other areas. These cases should serve as a warning call to other states and localities that an index case of malaria should initiate immediate surveillance for the parasite."