Harr Parasitology Practice Test 2026 – Complete Exam Prep Guide

In the context of a waterborne outbreak of diarrheal disease, Giardia lamblia and Cryptosporidium spp. are the most relevant organisms. Both of these protozoan parasites are well-documented causes of gastrointestinal illness that can be spread through contaminated water sources.

Giardia lamblia, commonly known as giardiasis, infects the intestines and leads to symptoms such as diarrhea, abdominal pain, and bloating. It is known to be resistant to typical disinfection methods used in water treatment, allowing it to persist in contaminated water supplies.

Cryptosporidium spp. is another important waterborne pathogen that causes cryptosporidiosis. It also results in diarrhea and can persist in water systems due to its hardy oocyst form, which can withstand chlorine disinfection. The outbreaks associated with these two pathogens are often linked to drinking water contamination or recreational water activities.

In comparison, while Entamoeba histolytica is a pathogenic amoeba that can cause dysentery and is transmitted fecal-orally, it is less commonly associated with waterborne outbreaks than Giardia and Cryptosporidium. Endolimax nana is a non-pathogenic amoeba and does not cause diarrhea. The other organisms mentioned, such as Blastocyst