The strain is relatively mild and can be easily treated, they said. Both were given antibiotics and are recovering.

Still, the discovery has prompted officials in Maryland, less than a mile from one of the infected pools, to call in a military team of experts to help eradicate infected mosquitoes, Montgomery County health official Lynn Frank told the Washington Post.

In Loudoun County, new traps and more larvicide are being used.

The anopheline mosquitoes found carrying malaria are not believed to be from the same pool that infected the teens since that type of mosquito rarely travels more than a half-mile, said David Goodfriend, director of Loudoun's health department. Officials also don't believe the teens were the source of infection in the two pools.

"There is malaria out there, and we have to pay attention to it," said Richard W. Steketee, chief of the malaria epidemiology branch at the Centers for Disease Control and Prevention ( news - web sites) in Atlanta.

Of the estimated 1,200 cases of malaria in the United States each year, most are found among immigrants from countries where malaria is common. The illness can be deadly.