Current scenario of dwarf threadworm, Strongyloides stercoralis infections in Southern Rajasthan, a systemic review
Strongyloides stercoralis is an intestinal nematode in humans. It is estimated that tens of millions people are infected worldwide, although no precise estimate is available. Although most infected individuals are asymptomatic, S. stercoralis is capable of transforming into a fulminant fatal illness under certain conditions associated with a compromise of host immunity. Strongyloides stercoralis has a complex biology with two separate life cycles, the freeliving cycle and the parasitic cycle. Filariform larvae in the soil infect the human host by penetration of intact skin to begin the parasitic cycle. The larvae enter circulation, are transported to the lungs, penetrate alveolar spaces, ascend the bronchial tree, are swallowed and reach the small bowel. The larvae migrate into the lumen and are either passed into feces or mature into filariform larvae, which can infect the intestinal mucosa or skin of the perianal region to restart the parasitic cycle. Rhabditiform larvae passed into feces can become infectious filariform larvae directly or go through a free-living cycle of development in the soil. This adaptability allows for the parasite's survival in the absence of mammalian hosts. Pulmonary symptoms such as a cough and tracheal irritation, mimicking bronchitis, occur as larvae migrate through the lungs several days later. Gastrointestinal symptoms (diarrhea, constipation, anorexia, abdominal pain) begin about 2 weeks after infection, with larvae detectable in the stool after 3 to 4 weeks.Techniques are periodically used to improve the sensitivity to detect Strongyloides larvae in stool samples. Various other standard methods that increase the sensitivity of diagnosis are larval concentration and culture methods, including Baermann, formalin-ethyl acetate sedimentation techniques, Harada-Mori, charcoal filter paper, and blood agar culture plate methods.
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