Strongyloides stercoralis

Strongyloides stercoralis is a human pathogenic parasitic roundworm causing the disease strongyloidiasis. Its common name is threadworm. In the UK and Australia, however, the term threadworm can also refer to nematodes of the genus Enterobius, otherwise known as pinworms. The Strongyloides stercoralis nematode can parasitize humans. The adult parasitic stage lives in tunnels in the mucosa of the small intestine. The genus Strongyloides contains 53 species, and S. stercoralis is the type species. S. stercoralis has been reported in other mammals, including cats and dogs. However, it seems that the species in dogs is typically not S. stercoralis, but the related species S. canis. Non-human primates are more commonly infected with S. fuelleborni and S. cebus, although S. stercoralis has been reported in captive primates. Other species of Strongyloides that are naturally parasitic in humans, but with restricted distributions, are S. fuelleborni in central Africa and S. kellyi in Papua New Guinea. S. stercoralis infection is associated with fecal contamination of soil or water. Hence, it is a very rare infection in developed economies. In developing countries, it is less prevalent in urban areas than in rural areas (where sanitation standards are poor). S. stercoralis can be found in areas with tropical and subtropical climates. Strongyloidiasis was first described in the 19th century in French soldiers returning home from expeditions in Indochina. Today, the countries of the old Indochina (Vietnam, Cambodia, and Laos) still have endemic strongyloidiasis, with the typical prevalences being 10% or less. Regions of Japan used to have endemic strongyloidiasis, but control programs have eliminated the disease. Strongyloidiasis appears to have a high prevalence in some areas of Brazil and Central America. It is endemic in Africa, but the prevalence is typically low (1% or less). Pockets have been reported from rural Italy, but the current status is unknown. In the Pacific islands, strongyloidiasis is rare, although some cases have been reported from Fiji. In tropical Australia, some rural and remote Australian Aboriginal communities have very high prevalences of strongyloidiasis. In some African countries (e.g., Zaire), S. fuelleborni was more common than S. stercoralis in parasite surveys from the 1970s, but the current status is unknown. In Papua New Guinea, S. stercoralis is endemic, but prevalence is low. However, in some areas, another species, S. kellyi, is a very common parasite of children in the New Guinea Highlands and Western Province.