Losing the Race Against Malaria
New drugs needed to stop rising rates of infection, scientist contends
WEDNESDAY, Oct. 15, 2003 (HealthDayNews) -- Drug researchers are losing the race against malaria, and Americans and Europeans should be more concerned than they are.
That's the assessment of an Israeli disease specialist whose warning appears in the Oct. 16 issue of the New England Journal of Medicine.
However, one U.S. expert says major efforts to develop new medicines are under way.
Malaria is a major health problem in tropical regions, with an estimated 500 million new cases causing at least 1 million deaths every year there.
The issue should be "one of the major concerns for travelers to the tropics," says Dr. Eli Schwartz, director of the Center for Geographic Medicine at the Chaim Sheba Medical Center in Tel Hashomer.
"The estimate is for more than 70 million people traveling from Western countries to endemic areas," he says. "There are about 30,000 cases of malaria annually in returning travelers in Europe alone."
Another reason for American concern is that "malaria can be a problem for the [U.S.] troops in Iraq as well as Afghanistan, and the regular anti-malaria drugs should not help for the type of malaria that exists there," Schwartz says.
Many American troops who went to Somalia several years ago and those dispatched recently to Liberia came down with malaria, Schwartz notes.
A growing number of western travelers are developing malaria, even though they take the drugs recommended for malaria prevention, Schwartz says. Many of those cases develop weeks or even months after a traveler's apparent safe return, the journal report says.
There were 300 cases of malaria among Israeli travelers to regions where malaria is endemic between 1994 and 1999, and 134 of those cases were diagnosed more than two months after the traveler's return, Schwartz says. In the United States, 2,882 travelers developed malaria between 1992 and 1998, with 987 cases diagnosed weeks or months later.
And most of those cases were not caused by carelessness. More than 80 percent of the infected Israelis and 60 percent of the Americans had dutifully taken the drugs designed to prevent the disease. Those failures were due to the complex nature of the microbes that can cause malaria and growing resistance to existing drugs, Schwartz says.
Malaria is transmitted by infected mosquitoes. Symptoms can include fever and flu-like illness, including shaking, chills, headache, muscle aches and tiredness. If not treated promptly, one type of malaria, Plasmodium falciparum, may cause kidney failure, seizures, mental confusion, coma and death.
Four species of Plasmodium microbes can cause malaria, and they act in different ways. Two species, called P. vivax and P. ovale in medical shorthand, take up residence in liver cells, eventually emerging into the blood to cause the disease. The most dangerous species, P. falciparum, moves out of the liver into the blood in just a few days.
Several drugs and drug combinations are available for prevention of malaria. Three of the currently used medications -- mefloquine, doxycycline and chloroquine -- attack the microbe in the blood. They must be taken for at least four weeks after a traveler returns home. A fourth, primaquine, acts in the liver and can be discontinued as soon as the traveler leaves the region of endemic disease, experts say.
The late-onset cases that strike even though the traveler takes the recommended drug regimen occur because the drugs act only against microbes in the blood, Schwartz says. So microbes that can survive in the liver emerge later to cause the disease.
"One of the main goals of our paper is to call the pharmaceutical companies to work on new drugs that will shoot the malaria parasite in the proper place, meaning the liver," Schwartz says.
Dr. Thomas E. Wellems is chief of the Laboratory for Malaria and Vector Research at the National Institute of Allergy and Infectious Diseases. He says a major effort to develop new malaria drugs is under way. Much of the work is being done by public-private partnerships, notably the Medicines for Malaria Venture, based in Geneva.
"Much of the effort is focused on the killer strain, P. falciparum," Wellems says. "This is increasingly important now that strains resistant to chloroquine have spread throughout the world. Death rates have resurged since they reached their lowest levels in the 1980s."
Today's effort to develop new anti-malarial drugs "is greater even at the former height of malaria research, during World War II," Wellems says.