Schistosomiasis infects humans at which of the following stages of it’s life cycle?
Correct Answer: Cercariae
Description: In water, eggs hatch to form miracidia, which invade snail. Cercariae from snail traverse human skin and vascular system. Definitive diagnosis of schistosomiasis requires the recovery of the characteristic eggs in urine, stool, or biopsy specimens. In S haematobium infections, eggs are most numerous in urine samples obtained at midday. When examination of the sediment yields negative results, eggs may sometimes be recovered by filtering the urine through a membrane filter. Cystoscopy with biopsy of the bladder mucosa may be required for the diagnosis of mild infection. Eggs of S mansoni and S japonicum are passed in the stool. Concentration techniques such as formalin, ether or gravity sedimentation are necessary when the ova are scanty. Results of rectal biopsy may be positive when those of repeated stool examinations are negative. Ref: Ray C.G., Ryan K.J. (2010). Chapter 56. Trematodes. In C.G. Ray, K.J. Ryan (Eds), Sherris Medical Microbiology, 5e.
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