A patient presents with watery diarrhea, abdominal cramps, and nausea after consuming contaminated water from a stream during a camping trip. Laboratory tests reveal oocysts in the stool sample. Which of the following parasites is most likely responsible for this infection?
Correct Answer: C
Rationale: Cryptosporidium parvum is a parasite commonly found in contaminated water sources such as streams or lakes. It causes an infection called cryptosporidiosis, which often presents with symptoms like watery diarrhea, abdominal cramps, and nausea. The oocysts of Cryptosporidium parvum can be identified in stool samples, making it the likely culprit in this scenario. Giardia lamblia, another common waterborne parasite, can also cause similar symptoms but is characterized by trophozoites rather than oocysts in stool samples. Entamoeba histolytica is associated with amoebic dysentery and does not typically present with watery diarrhea. Cyclospora cayetanensis is another parasite causing gastrointestinal symptoms but is not as commonly associated with contaminated water sources as Cryptosporidium parvum.