Strongyloidiasis

Strongyloidiasis, or Cochin-China diarrhea, is caused by a minute nematode, the threadworm Strongy-loides stercoralis. The organism was first discovered in 1876 in French troops who had suffered severe diarrhea in the Cochin-China region of Vietnam. Strongyloides occurs around the world, with a range similar to that of the hookworms. Millions of people harbor the organism. Because poor sanitation and going without shoes favor transmission, it is especially prevalent in poor tropical countries. Like hookworm disease, strongyloidiasis prevalence has declined greatly in the southern United States since the early twentieth century, but it still exists in foci in Kentucky and other states.

The worm has a complex life cycle. Parasitic males may not exist, but if they do, they are eliminated from the body shortly after infection. The females burrow in the mucosa of the intestine, where they feed and lay their eggs, apparently by parthenogenesis. The eggs pass into the lumen of the intestine, where they hatch into a rhabditiform larval stage. In most cases these larvae are voided in the feces to the soil and either transform themselves directly into an infective filariform larval stage, or, if conditions are favorable, undergo one or more generations of sexual reproduction before filariform larvae appear. Like the hookworms, the filariform Strongyloides larvae penetrate human skin, often on an unshod foot, enter the venous circulation, and are carried through the heart to the lungs. Here they burrow through the walls of the air sacs, ascend to the throat, and are swallowed. The adult females bore into the walls of the small intestine and sometimes into the wall of the large intestine as well. Autoinfection is also possible and can maintain the parasite for years after the host has left endemic areas. In this variation of the life cycle, rhabditiform larvae develop into infective filariforms while still in the intestine. These larvae penetrate the mucosa, enter the bloodstream, and are eventually swallowed to continue the cycle.

Migrating larvae may produce itching when they penetrate the skin, and cough and chest pain when they are active in the lungs. Light intestinal infections are often asymptomatic, but heavier worm loads may cause abdominal pain, nausea, alternating diarrhea and constipation, anemia, weight loss, and low fever. Autoinfection can produce an enormous number of worms and can be fatal. Persons with immune deficiencies from diseases such as cancer or acquired immune deficiency syndrome, or whose therapy requires immune suppression, may develop devastating hyperinfections from mild or inapparent strongyloidiasis.

Diagnosis is made by detection of larvae in stool specimens. Therapy is usually effective, although side effects from drugs are common. Prevention is largely a matter of education and better living conditions. Improved rural sanitation and wearing shoes break the worm's life cycle in most cases, and treatment prevents autoinfection.

Strongyloides fiillehorni, a parasite of monkeys, has been found in many people in Zaire, Zambia, and other central African countries; larvae may possibly be transmitted in mother's milk. The same or a very similar species has been found in 80 to 100 percent of infants in a region of Papua New Guinea.

K. David Patterson

Constipation Prescription

Constipation Prescription

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