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Chapter 13

Strongyloidiasis; Angiostrongyliasis

The importance of strongyloidiasis, and medical opinion concerning the nature and clinical significance of the causative nematode, Strongyloides stercoralis, has fluctuated widely in the past century. The nematode was first discovered in 1876 in French soldiers who had been in Cochin China (now Vietnam), but for years it was considered an innocuous parasite. However, in the last 40 years it has been recognized that in many patients this worm can cause severe inflammatory and ulcerative bowel disease as well as malabsorption and even death. The infection is of special significance in people who are immunosuppressed, either therapeutically or naturally; in these patients the character of the disease becomes much more severe, with hyperinfection and serious pulmonary as well as intestinal complications.

Even the life cycle of the worm is complex. It has three phases and the parasitic female can reproduce without the aid of the parasitic male - whose very existence is disputed! The female S. stercoralis has the capacity to adopt a parasitic as well as a free-living mode of life depending on the environment in which it finds itself. Strongyloidiasis is the only helminthic infection where the parasite/worm burden can increase in the host without reinfection from an outside source; in this respect it acts more like a protozoan parasitic disease. It is widespread not only in the tropics but also in temperate countries, especially in institutions where hygiene is poor and where inmates are unable to care for themselves. It is one of the few worms which is more prevalent in adults than children. There are characteristic radiological changes which permit the alert radiologist to suggest the diagnosis before it is suspected by his clinical colleagues. Any disease in which this is possible MUST be of interest to radiologists!

Synonyms

Strongyloidiasis. Strongyloidosis. Strongulosis. Strongyliasis. Cochin China diarrhea.

Sp: Estrongiloidosis. Estrongilosis. Fr: Strongyloidose. Anguillulose. Ger: Strongyloidesbefall

Definition

Strongyloidiasis is a zoonotic infection by the nematode Strongyloides stercoralis, or rarely S. fülleborni, with man as the most important host.

Geographic Distribution

Strongyloides stercoralis is most common in the warm, moist regions of the tropics (particularly Brazil, Colombia and Southeast Asia), but is found worldwide and in all climates. It is endemic in Puerto Rico and the southeastern United States, where it can be found in 3-4% of rural Kentucky schoolchildren and in 4% of college students from the Appalachian highlands, as well as in 6% of hospitalized patients from Kentucky, Tennessee, North Carolina, and Virginia (Davidson, 1992). In some population groups, such as recent immigrants, veterans of foreign wars, prisoners, and residents in long-term care facilities, the infection rate is even higher. In the state of New York, up to 18% of certain subgroups, such as debilitated children or immunosuppressed patients, have been found to be infected (Devault, 1990; Lessnau, 1993). Infections in temperate zones are most frequent in institutions, such as mental hospitals, and prisons, where it is difficult to maintain an adequate standard of personal hygiene. Strongyloidiasis is most common in adults, but occurs in children as well, especially where they are institutionalized, as in orphanages and homes for retarded children, hospitals, and prisons. Although usually a benign though troubling infection in those with competent immunity, it may kill those who are immunosuppressed or immunocompromised. Strongyloides fülleborni infections occur occasionally in tropical Africa, particularly the Democratic Republic of the Congo, and also in Papua New Guinea.

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