Treating Tropical Diseases

by Food and Drug Administration (FDA)

When adventurer Sandra Levy, 61, of Short Hills, N.J., visited Ecuador and the Galapagos Islands in December 1993, she tried to protect herself against tropical diseases and the insects that transmit them.

Before leaving home, Levy got vaccinated against yellow fever and took medicine to ward off malaria.

At the headwaters of the Amazon River, she took precautions. Whether trekking into the jungle or canoeing across the river to see leaf-eating ants on the opposite bank, she wore long-sleeved shirts and knee-high boots and used an insect repellent containing DEET. In her thatch hut at night, she slept under mosquito netting.

After she returned home, however, Levy noticed a sore the size of a dime above her left ankle. "It didn't hurt or itch," she says, "but it didn't go away. I decided to see my dermatologist."

By the end of March, despite antibiotics, her sore had grown to the size of a silver dollar, so she made another medical appointment. "The doctor took a biopsy. Knowing I'd been in Ecuador, he had the lab check for deep fungus and leishmaniasis."

The diagnosis was indeed leishmaniasis, a tropical disease spread by infected female sandflies. Levy's doctor put her in touch with a tropical disease specialist for treatment.

As Levy's experience shows, travelers' precautions against tropical diseases are not foolproof.

"The American public shouldn't be complacent about these diseases," says Randolph Wykoff, M.D., associate commissioner for operations at the Food and Drug Administration. "Tropical diseases are absolutely devastating in other countries, killing hundreds of thousands of people. We are not immune." While most such infections are acquired during travel, Wykoff says, some people can also become infected from other travelers who bring home the disease.

Still, tropical diseases are more prevalent in developing countries, where conditions all too commonly foster their spread. War refugees migrating to other areas carry infections with them. Economic and social crises stress health systems. And unsanitary conditions due to rapid urbanization and rapid population growth foster an environment in which insects and other animals can transmit disease-producing organisms.

"King" Malaria

Sometimes called the King of Diseases, malaria yearly strikes up to 500 million people, 90 percent of them in Africa, with up to 2.7 million deaths, mostly young children.

Malaria is caused by four species of Plasmodium parasites, transmitted to humans by infected female Anopheles mosquitoes. Symptoms include a spiking fever, shaking chills, and flu-like symptoms. Anemia or liver problems may develop. If treatment is delayed, severe infection may lead to kidney failure, coma, and death.

Malaria kills so many African children because they lack immunity, says tropical disease specialist LTC Alan Magill, M.D., of Walter Reed Army Institute of Research, Department of Defense. Americans in Africa — travelers or troops — also are at risk because their immunity to malaria is like a child's, he says. They have more severe malaria than Africans who have survived past age 5 and developed immunity. "At our study site in Kenya," he says, "if you drew blood from 100 seemingly normal Africans at the local market, you'd find malaria parasites in most of their bloodstreams. They're infected, and the transmission cycle goes on, but they don't have obvious ill effects."

The national Centers for Disease Control and Prevention gets about 1,000 reports a year of malaria in the United States. Since 1957, nearly all these cases were acquired in areas of the world where malaria is known to occur.

Domestic malaria, in fact, was declared eradicated in this country in the 1940s. But from 1957 through 1994, CDC got 76 reports of malaria cases that may have been transmitted locally, including some from suburban New Jersey in 1991 and New York City in 1993. A 1995 report from Michigan was the first that far north since 1972. "In most cases, evidence indicated that locally infected mosquitoes did transmit the disease," says CDC malaria expert Lawrence Barat, M.D. "Anopheles mosquitoes are present throughout the contiguous United States. But we've never found an infected mosquito in the United States. More recently, we've had outbreaks of Plasmodium falciparum malaria, the more severe form. We want to monitor this very closely."

For several decades after the Second World War, the drug of choice for malaria treatment and prevention was chloroquine (Aralen and generics). "The drug was well-tolerated, fast-acting, and cost only 9 cents to cure a child," says Robert Gwadz, Ph.D., assistant chief, Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases (NIAID). However, in the 1950s, he says, resistance to chloroquine in falciparum malaria appeared in South America and Southeast Asia and spread throughout both continents and eventually into Africa. "Chloroquine is now useless in most malarious areas."

FDA has since approved numerous anti-malaria drugs. Many are not marketed here or are used here only for indications other than malaria.

Chloroquine remains the treatment of choice for patients with malaria caused by species still susceptible to the drug. Resistance to chloroquine is becoming more common, however, and alternative drugs are necessary.

About the Author

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