Tropical Diseases - Schistosomiasis

A worm of a different sort—the tre-matode, a flatworm of the class Trematoda , which includes the flukes—is responsible for schistosomiasis . This disease occurs in various forms in Africa, Asia, South America, and the Caribbean, including Puerto Rico. About 200 million people are infected with schistosomiasis, also called bilharziasis .

Life Cycle of the Fluke Parasite

The process of infection by one kind of fluke involves free-swimming larvae that penetrate the skin of a human who has entered waters containing the organism. The larvae follow the human bloodstream to the liver, where they develop into adult worms. The adult worms then move into the blood vessels of the host and lay eggs. Some of the eggs find their way into the intestine or urinary bladder and are excreted with the urine or feces of the host. If they find their way to fresh water, the eggs hatch and the released organisms find their way to the body of a snail. Inside the snail they multiply into thousands of new larvae over a period of one or two months, after which they return to the water and invade the skin of another human. In this manner the fluke worm continues its life cycle, infecting more humans who venture into the contaminated waters.


Skin rashes and itching, loss of appetite, abdominal discomfort, and diarrhea are among early symptoms of schistosomiasis infections. There also may be fever and generalized aches and pains. During a period of from one to two or more months after the initial infection, more severe symptoms may occur as a result of a growing number of adult worms and eggs in the body, which produce allergic reactions. Those symptoms may include diarrhea, abdominal pain, coughing spells, and high fever and chills. Medical examination may reveal a tender and enlarged liver plus signs of bleeding in the intestinal tract. Complications may result from obstruction by masses of worms and eggs or by rupturing of the walls of body organs during migration of the organisms. Diagnosis usually can be confirmed by examination of the victim's stools or of the lining of the rectum for the presence of eggs of the fluke worms.


Therapy may consist of administration of antimony-based drugs, tartar emetic, measures to relieve the symptoms, and, when deemed necessary, surgery. In some cases, a medication may be administered to flush the eggs of the fluke worm through a specific part of the circulatory system during a surgical procedure in which a filter is inserted in a vein to trap the eggs; thousands of fluke worms can be removed by this technique. Some of the medications used in treating schistosomiasis can have serious side effects and are used cautiously. However, the alternative may be prolonged emaciation of the victim, with a bloated abdomen and early death by cancer or other causes related to the infection. The female fluke worm has been known to continue depositing eggs during a life span of 30 years, causing frequent recurrence of acute symptoms.

Other Forms of Schistosomiasis

There are several other forms of schistosomiasis that cause variations in symptoms. One kind involves the liver and central nervous system, resulting in death of the victims within as little as two years after infection. Another form seems to involve the urinary bladder, causing frequent, painful, and blood-tinged urination with bacterial infection as a complication.

Swimmer's Itch

A mild form of schistosomiasis is known by the popular name swimmer's itch . It can occur anywhere from Asia to South America and as far north as Canada and western Europe, affecting bathers in both fresh water and sea water. As in the severe forms of schistosomiasis, snails are the intermediate hosts, and wild animals and birds provide a reservoir of the organism. The effects are treated as a skin allergy, and shallow local waters used for swimming are treated with chemicals to eradicate the snails. Careful drying and examination of the skin after swimming in possibly infected waters can control to some degree the invasion of the skin by fluke larvae. A chemical skin cream that tends to repel fluke larvae also is available as a protective measure.

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