Tropical Diseases: Flatworms, Snails, Schistosomiasis, Leishmaniases ...

by Food and Drug Administration (FDA)

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Flatworms, Snails and Schistosomiasis

Flatworms cause schistosomiasis. First-stage larvae infect freshwater snails, then evolve into cercariae larvae, which exit the snails and swim along to find a human host. Penetrating the skin, male and female cercariae move in the bloodstream to the intestines or bladder and mate. Eggs excreted in human waste end up in the water supply, restarting the cycle. About 200 million people worldwide are infected. Severe disease leads to about 200,000 deaths each year.

Most symptoms are due not to the worms, but to eggs trapped in tissue. Short-term infection may be symptomless or cause such symptoms as fever, itchy rash, headache, joint and muscle pain, diarrhea, and nausea. Chronic infection can damage the liver, kidneys and bladder, or intestines. FDA has approved praziquantel (Biltricide) as treatment.

Places where schistosomiasis is most prevalent include Brazil, Puerto Rico, and St. Lucia (an island in the East West Indies); Egypt and most of sub-Saharan Africa; and Southern China, the Philippines, and Southeast Asia, according to CDC. At greatest risk are people who wade, swim or bathe in fresh water in rural areas where sanitation is poor and snail hosts are present.

Travelers to such areas should not swim in fresh water; salt water like the ocean and chlorinated pools are considered low risk. Bathing water should be heated to 50 degrees Celsius (122 degrees Fahrenheit) or treated with iodine or chlorine, as for drinking. Filtering water with paper coffee filters may remove the parasites. If these methods are impossible, CDC recommends that travelers let bathing water stand three days; cercariae rarely live longer than 48 hours.

WHO-led researchers are planning to test a vaccine in humans.

Trypanosoma Diseases: Sleeping Sickness, Chagas' Disease

The parasites Trypanosoma brucei gambiense and T. brucei rhodesiense cause African sleeping sickness. About 20,000 cases worldwide are reported yearly. Infected tsetse flies, which bite during the day, transmit this extremely serious disease.

East Africa's sleeping sickness, due to T. brucei rhodesiense infection, causes symptoms within days to weeks. West Africa's chronic gambiense variety may not cause the "sleeping" part of the illness until months to years after exposure. Symptoms include fever, headache, lethargy, and confusion, which may progress to convulsions, coma and death.

Suramin, available from CDC, is for the early stages of both gambiense and rhodesiense sleeping sickness. Melarsoprol, an arsenic derivative, is also available from CDC to treat final stages of both varieties. If the patient is known to have gambiense, however, the drug eflornithine (Ornidyl), approved by FDA, is more effective and safe because melarsoprol can cause serious, even fatal, nervous system problems in some patients. Eflornithine is useful for both early and late stages of gambiense sleeping sickness; it is not effective for rhodesiense sickness.

Trypanosoma cruzi causes Chagas' disease, which affects at least 16 million people in Central and South America. The parasite infects reduviid bugs. When the bugs defecate, they deposit the parasite, which can enter a human through a break in the skin or through a mucous membrane, such as that which lines the nose, mouth or eyes. The best prevention is to avoid potential reduviid habitats — mud, adobe and thatch buildings, especially those with cracks or crevices. If this isn't feasible, spraying infested areas and using bed nets can help prevent infection.

In its short-term stage, Chagas' disease may cause no symptoms or may cause fever, swollen lymph nodes, and inflammation of the heart or, rarely, the brain. Deaths occur, mainly in children, but most patients survive, their symptoms usually disappearing after four to six weeks. Many years later, about a fourth of patients develop serious, sometimes fatal, heart infection or damaged digestive organs such as an enlarged esophagus or colon for the long term. Nifurtimox is available from CDC for the treatment of short-term Chagas' disease. There is no accepted anti-parasitic treatment for chronic illness.

About 70 percent of cases occur in Argentina, Bolivia, Brazil, Chile, Paraguay, and Uruguay. In 1991, the health ministers of those six countries began a program to eliminate Chagas' disease by the end of this century. Since then, house infestation has declined 75 to 98 percent in some areas, PAHO reports.

The Leishmaniases

Sandra Levy is one of an estimated 12 million people worldwide with leishmaniasis. This group of diseases is spread through the bite of female sandflies infected with any of about 20 different species of Leishmania parasites.

Levy had cutaneous leishmaniasis, which causes skin sores that may leave ugly scars. Mucocutaneous leishmaniasis can cause disfiguring destruction of membranes in the nose, mouth, or upper throat (pharynx).

In visceral leishmaniasis, parasites invade internal organs, causing death if the symptoms are untreated. According to the Defense Department's Magill, "You have chronic fever, depression of bone marrow and blood cells, weight loss, and a huge spleen so full of parasites it comes down into the pelvis." Years may pass before symptoms appear.

About the Author

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