NAVAL STATION ROTA, Spain — The first sick Marines arrived aboard the ship from Liberia with their skin riddled with mosquito bites. They became so ill that doctors planned to fly them hundreds of miles away to Germany for more care.

That night, 15 more Marines arrived on the USS Iwo Jima. Some had high fevers and high blood pressure. Many were throwing up and had severe diarrhea. By the next day, 31 Marines were seriously ill and nobody knew why.

In West Africa, a place known for having some of the world’s worst infectious diseases, the list of possible causes was startling.

“We had no clue what it was,” said Lt. Chris Scuderi, a doctor aboard the Iwo Jima.

Fearing that they had a epidemic on their hands, doctors scrambled to identify the illness before it spread. At the same time, they had to save the ill Marines.

Lab tests performed on the ship days later would show that the servicemembers had the deadliest form of malaria, a parasitic infection spread by mosquitoes that is not contagious.

More than a month later, the ship’s medical staff are not certain what caused the outbreak among military personnel, who were in Liberia as part of a peacekeeping mission in mid-August.

One-third of the people sent to the West African country came down with malaria, according to the Pentagon. Eighty of the 200 Navy, Marine Corps and Department of Defense personnel developed a strain of malaria that kills 25 percent of its victims.

Those inflicted are now doing well, commanders say, but the Center for Disease Control and the Department of Defense is investigating why so many developed malaria. Doctors had prescribed anti-malarial pills to everyone deployed to the region.

Medical experts are looking at several possibilities. They include whether the strain of malaria has become resistant to the type of drugs the troops were taking, whether the drug was not powerful enough or whether troops didn’t take the drug at the prescribed times.

At the onset of the outbreak, the ship’s medical staff thought the illness could have been something other than malaria.

Their biggest concern was that it was Lassa fever, a viral infection found in West Africa that is highly contagious. Medical personnel had to wear protective suits until tests ruled that out.

Rumors and fear had spread around the ship faster than any contagious disease. Doctors rushed to find out what was wrong and to stabilize patients so they could be airlifted to Lanstuhl Regional Medical Center in Germany. Doctors, nurses and lab technicians worked nonstop.

The day after the first sick Marines arrived on the Iwo Jima, Petty Officer 1st Class Samuel Henry, a Navy hospital corpsmen on the ship, discovered malaria on a blood smear under a microscope. It reassured doctors.

“We knew what we were facing,” Scuderi said.

Those who were evacuated to Landtuhl and Bethesda, Md., with serious cases are now doing fine, said Col. Andrew Frick, commander of the 26th Marine Expeditionary Unit, the group sent ashore to Liberia. One Marine who had a serious case of malaria might be medically discharged.

The result could have been much worse, Frick said. He credits the quick work of the medical staffs aboard the three ships for saving them.

The three-ship Iwo Jima Amphibious Ready Group is in Rota this week for a port call before heading home after completing an eight-month deployment.

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