Giardia lamblia, a human parasite found in contaminated drinking water, is responsible for over 20,000 intestinal infections a year in the U.S. A single-celled eukaryote, Giardia enters the body in unfiltered water or I transmitted through person-to-person contact. It eventually makes its way to the intestine, where it lives as a trophozoite, and undergoes asexual reproduction.
Symptoms of giardiasis include abdominal cramps, vomiting, fever, and diarrhea. Once it is expelled from the body through stool, it assumes the form of an infectious cyst that can survive in water, soil, or on surfaces for weeks.
In this image, the trophozoites' microtubule skeletons are immunostained (red), while their paired nuclei are DAPI stained (fluorescent blue).