A 4-year-old child presents with acute watery diarrhea and abdominal cramps. Stool microscopy reveals trophozoites with falling leaf motility without RBCs and pus cells. The etiological agent is:

Ans. is 'b' i.e., Giardia lamblia(Ref: D.R. Arora, p. 43)* Mature cyst is the infective form of the parasite acquires infection by contaminated water and food. Infection may be acquired by anal oral sexual practices among male homosexuals.* Within 30 minutes of ingestion excystation occurs in the duodenum, cyst hatches out two trophozoites which multiplies and colonize in duodenum and upper part of jejunum.* In acute Giardiasis trophozoite show the typical 'falling-leaf' motility in wet mount examination of faeces.