KABUL — Canadian military doctors are keeping a close eye on the 2,000-plus Canadians and others based at Camp Julien after diagnosing five confirmed cases of malaria in the last two weeks.

Doctors fear the two American soldiers, one Canadian soldier and two civilian workers -- a Canadian and a Nepalese -- may be just "the tip of the iceberg."

They have put out word to all who are staying at the base to report immediately to the clinic if they develop fevers, but due to the incubation period of the parasite that causes the disease, it may not be known for a year just how widespread the outbreak is, said Capt. Michael Hughson.

"We are either the smartest doctors in the world, or there are more cases out there," said Hughson, a Canadian army physician from Fredericton.

The first cases turned up June 7 and June 8 when two U.S. soldiers who had both been previously based in different parts of southern Afghanistan turned up at the base hospital.

"When I saw the first American, it was a diagnosis I made basically walking through the door," said Hughson, who has become the camp's acknowledged expert on the disease.

"The patient was shaking all over. He looked like somebody that had a really extreme flu."

And that's what Maj. Joel Potts thought he had, though he'd never had a flu like this.

"It's probably the most miserable time of my life," Potts, a full-time National Guardsman from Stringtown, Okla. "The headache was kind of indescribable -- tremendous pain. Your body aches all over, from head to toe. It's like you have a super-flu or something."

Sgt. Guy Bergeron, a laboratory technician from Sherbrooke, Que., who saw malaria patients from East Timor, detected low white blood cell and platelet counts and identified the disease -- and the strain -- within 24 hours.

It took more than a week to get backup confirmation from U.S. technicians at the nearby American base in Bagram.

The other cases came in last week, and test results were confirmed Sunday.

Spread by a parasite that is transmitted to humans through mosquito bites, malaria is believed to have originated in Africa.

"It is a disease of human history, because it can only live on humans it expanded through the world with humans," said Hughson.

About 41 per cent of the world's population lives in malarial areas, mostly near the equator and south of it, and between 700,000 and 2.7 million people die from the disease each year.

Malaria, however, need not be fatal and, contrary to popular belief, is no longer necessarily a lifelong disease that comes and goes with fits of chills, fever, sweats, nausea and aches.

The parasite typically needs an ambient temperature of 20 degrees Celsius and an altitude of less than 2,000 metres to survive. At 2,100 metres, Kabul is right on the borderline.

Afghanistan was not known as a particularly virulent malaria region until after the Soviet invasion of 1980, when the bombing of irrigation systems created stagnant pools all over the country in which mosquitoes thrive.

There are four major strains of malaria and the Kabul area is known for harbouring the worst of them, plasmodium falciparum, a rapid, potentially fatal strain that is mercifully more easily treatable than the others.

The five patients at Camp Julien are believed to have plasmodium ovale or vivax, recurring strains of the disease that are not especially drug resistant and can be treated over time, Hughson said.

But both the latter forms of malaria can lie dormant in the liver for months before they show themselves or cause a relapse.

Hughson said the disease can be deceiving. Patients can have an initial round of fever that lasts just a few days, which they write off as the flu. But the recurrence -- days, weeks or months later -- can be a doozy.

Treatment usually involves a three-day round of chloroquine, a synthetic form of the quinine that British colonizers in India would drink in their gin-and-tonics.

That kills the parasite in the blood. But doctors also have to follow that up with a two-week regimen of a strong drug called primaquin that itself can make patients sick.

Potts, a lean, hard veteran who had been taking his anti-malarial pills every Monday, said he had the most trouble with the chloroquine.

"I'll tell you, the cure is pretty tough," he said. "I was very weak, no appetite. It's a very difficult three days but it's three days you have to endure."

Potts is already on his primaquin regimen and is feeling stronger every day. He has returned to work half-days.

Doctors still don't know if the Americans brought the malaria into camp from lower altitudes down south or if they contracted the disease in Kabul, which just experienced its wettest spring in years.

"The blood of the two Americans is already, I wouldn't say normal, but it is normalizing," said Hughson.

The doctor said he is anxious to identify carriers of the disease on the base because, if they are subsequently bitten by a virgin mosquito, that mosquito can spread the disease to others within 12 to 20 days.

Hughson said there is some evidence that soldiers are adhering more strictly to their hated once-a-week mefloquin pill.

The medicine is notorious for its ability to induce weird dreams, or even psychosis, and compliance with the regimen has been "somewhat less than 100 per cent," said Hughson.

Troops also are supposed to use bug nets over their cots at night and to treat their nets and uniforms with insect repellent.

The two civilian employees of Cancap, a subsidiary of Quebec-based SNC Lavalin, had apparently not been advised to take preventive measures by company doctors in Canada.

Cancap staff in the camp say anti-malarial drugs are available if they want them, but the company has not recommended they take them.

"I think they have probably been getting some bad advice from their health-care providers," said Hughson, who added that any soldier or worker in Kabul who develops a fever in the next year should bring to the attention of their health-care provider the fact that they've worked in a malarial area.