In Haiti, the half-million people made homeless by the Jan. 12 earthquake now face another danger: malaria.

Also at risk are the relief workers who may not have built up an immunity to the sometimes-deadly strain found in Haiti.

On Thursday, the U.S. Centers for Disease Control and Prevention reported that 11 cases of the P.falciparum malaria infection, acquired in Haiti, have been confirmed among emergency personnel and Haitian residents who traveled to the U.S.

``Displaced persons living outdoors or in temporary shelters and thousands of emergency responders in Haiti are at substantial risk for malaria,'' said the CDC.

The cases include: seven emergency responders, including six military personnel; three Haitian residents who traveled to the U.S., including one Haitian adoptee; and one U.S. traveler.

Among the responders' cases, four of the cases were uncomplicated and treated in Haiti, while two were ``moderately to seriously ill'' and transferred to the United States for intensive care, the CDC said. All are expected to make a full recovery.

DANGEROUS STRAIN

Carried by mosquitoes, the P.falciparum strain of malaria is the predominant species in Haiti, the CDC said.

``Falciparum is the killer strain of malaria,'' said Dr. Gordon Dickinson, chief of infectious diseases at the UM Medical School, who just returned from four days at UM's field hospital in Port-au-Prince. ``It can cause intestinal hemorrhaging, cerebral inflammation or pneumonitis, which is an inflammation of the lungs. Cerebral malaria has a significant death rate.''

Nyka Alexander, a World Health Organization spokeswoman in Haiti, said the post-earthquake tent cities could create more malaria cases. ``There's a higher risk of malaria under current conditions,'' she said. When people live in such close quarters, an infected mosquito can come into contact with larger-than-normal numbers of people, she said.

Dickinson noted that P.falciparum is probably more dangerous to visiting volunteers who have no immunity to it than to Haitians who have lived with it all their lives.

Chloroquine pills taken before, during and after trips to Haiti may help prevent contracting the disease, he said.

Malaria symptoms include high fevers, shaking chills and flu-like illness, according to the CDC.

A YEARLY CYCLE

Each year, Haiti has 30,000 confirmed cases of malaria, though officials believe the actual number is closer to 200,000. A few dozen die each year, according to the CDC.

Alix Lassegue, executive director of Haiti's State University Hospital, said Tuesday that malaria cases are about where they've normally been this time of year, representing about five of every 100 patients who seek help because of a high fever.

It is after the rainy season, when stagnant water attracts more mosquitoes, that malaria is more of a concern, he said. Lassegue said it's possible that cramped, outdoor tent cities could exacerbate the problem.

Kristen Knutson, a spokeswoman for the United Nations' Office for the Coordination of Humanitarian Affairs, said Thursday that ``malaria is endemic to Haiti'' but that many instances of the disease can be prevented through the use of mosquito nets or simply wearing pants or long-sleeved shirts.

Miami Herald staff writer Michael Vasquez contributed to this report from Haiti.