![]() ![]() The initial sign of acute strongyloidiasis, if noticed at all, is a localized pruritic, erythematous rash at the site of skin penetration. kellyi is found in Papua New Guinea, and has not been reported elsewhere thus far. Sporadic cases have been reported from Southeast Asia. The vast majority of human infections are reported from sub-Saharan Africa. fuelleborni occurs in non-human primates throughout the Old World. Infections are most common in areas with poor sanitation, rural and remote communities, institutional settings, and among socially marginalized groups. Transmission has been reported during summer months in temperate areas. Strongyloides stercoralis is broadly distributed in tropical and subtropical areas across the globe. fuelleborni is a parasite of Old World apes and monkeys. ![]() stercoralis infections although it is unknown if they have a role as a natural reservoir. Domestic cats are experimentally susceptible to S. Two genetic populations have been found in domestic dogs, one that appears to only infect dogs and one that may infect both dogs and humans all human infections have been attributed to this second genetic population. However, patent infections with parasitic females have been detected in other primates (chimpanzees, monkeys, etc.) and domestic dogs. stercoralis is primarily a human parasite. kellyi to infants as a result of breastfeeding has been reported. stercoralis, autoinfection is believed to be impossible. Since eggs do not hatch within the host as with S. Parasitic females embedded in the submucosa of the small intestine and produce eggs via parthenogenesis (parasitic males do not exist). In the small intestine, larvae molt twice and become adult female worms. These larvae migrate via the bloodstream to the lungs, where they are eventually coughed up and swallowed, or reach the intestine via migration through connective tissue or abdominal viscera. The filariform larvae penetrate the human host skin to initiate the parasitic cycle. The free-living adults mate and produce eggs, from which more rhabditiform larvae hatch and eventually become infective filariform larvae. Eggs hatch shortly after passage into the environment, releasing rhabditiform larvae, that develop to either infective filariform larvae (direct development) or free-living adult males and females. stercoralis, with the important distinction that eggs (rather than larvae) are passed in the stool. Strongyloides fuelleborni follows the same life cycle as S. The significance of autoinfection in Strongyloides is that untreated cases can result in persistent infection, even after many decades of residence in a non-endemic area, and may contribute to the development of hyperinfection syndrome. Once the filariform larvae reinfect the host, they are carried to the lungs, pharynx and small intestine as described above, or disseminate throughout the body. ![]() Rhabditiform larvae in the gut become infective filariform larvae that can penetrate either the intestinal mucosa or the skin of the perianal area, resulting in autoinfection. The rhabditiform larvae can either be passed in the stool (see “Free-living cycle” above), or can cause autoinfection. The females live embedded in the submucosa of the small intestine and produce eggs via parthenogenesis (parasitic males do not exist), which yield rhabditiform larvae. In the small intestine, the larvae molt twice and become adult female worms. through abdominal viscera or connective tissue). However, 元 larvae appear capable of migrating to the intestine via alternate routes (e.g. It has been thought that the 元 larvae migrate via the bloodstream and lymphatics to the lungs, where they are eventually coughed up and swallowed. Parasitic cycle: Filariform larvae in contaminated soil penetrate human skin when skin contacts soil, and migrate to the small intestine. ![]() This second generation of filariform larvae cannot mature into free-living adults and must find a new host to continue the life cycle. The filariform larvae penetrate the human host skin to initiate the parasitic cycle (see below). In the free-living cycle: Rhabditiform larvae are passed in the stool of an infected definitive host, develop into either infective filariform larvae (direct development) or free-living adult males and females that mate and produce eggs, from which rhabditiform larvae hatch and eventually become infective filariform (元) slarvae. The Strongyloides stercoralis life cycle is complex, alternating between free-living and parasitic cycles and involving autoinfection. ![]()
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