What protozoan is one of the principal agents of traveler's diarrhea?

Giardia lamblia is one of the principal agents of traveler's diarrhea, a condition often encountered by individuals traveling to areas with poor sanitation and contaminated water supplies. This protozoan is a flagellated parasite that can inhabit the intestines of both humans and animals. Infection typically occurs through the ingestion of cysts present in contaminated water, undercooked foods, or through fecal-oral transmission.

Once Giardia lamblia is ingested, it can lead to symptoms such as diarrhea, abdominal cramps, bloating, and nausea, which are characteristic of traveler's diarrhea. The risk of this infection is particularly high when traveling to regions where hygiene practices are inadequate, and access to clean water is limited.

In contrast, while other protozoans like Entamoeba histolytica can also cause gastrointestinal illnesses, they are not as commonly associated with traveler's diarrhea. Cryptosporidium parvum is primarily associated with waterborne outbreaks and can cause diarrhea, but it is less frequently linked to individual cases of traveler's diarrhea compared to Giardia. Plasmodium falciparum, on the other hand, causes malaria, which is a completely different type of illness primarily transmitted by mosquitoes and not related to traveler's diarrhea. Thus, Giardia lam