Which protozoan is a principal agent of traveler's diarrhea?

• A. Entamoeba histolytica
• B. Cyclospora cayetanensis
• C. Cryptosporidium parvum
• D. Giardia lamblia

Answer: (D)

Traveler's diarrhea is most often linked to ingestion of water or food contaminated with fecal matter, and the protozoan most classically associated with this syndrome is Giardia lamblia. This flagellated parasite forms cysts that survive in water and are spread by the fecal-oral route, making untreated or inadequately treated water a common source for travelers. Once in the small intestine, Giardia disrupts fat absorption, producing greasy, foul-smelling stools, along with bloating and abdominal cramps. Other protozoa listed can cause diarrheal illness, but they are less typical as the primary cause of traveler's diarrhea: Entamoeba histolytica tends to cause invasive dysentery with blood, Cyclospora cayetanensis is linked to prolonged watery diarrhea often tied to specific foods, and Cryptosporidium parvum causes watery diarrhea especially in immunocompromised hosts. Giardia lamblia remains the most frequent protozoal agent in travelers.