Classification: Protist - group Mastigophora (flagellated protozoa)
Cell characteristics: Trophozoites - Heart-shaped; long, tapering posterior end; range in size from 9 to 21 micrometers by 5 to 15 micrometers. Two nuclei (look like a pair of eyes) with small karyosomes. Also, two median bodies and four pairs of flagella. Has a sucking disc that allows it to exist in the duodenum and to resist gut peristalsis.
Cysts - Smaller than trophozites (8 to 12 micrometers by 7 to 10 micrometers). Four nuclei with eccentric karyosomes are still visible. Cysts formed when colon is entered.
Source: Deer, beavers, cattle, cats, humans and other animals.
Pathogenicity: Causative agent of giardiasis or "hiker's diarrhea" and "beaver fever". Chronic diarrhea, dehydration, abdominal pain may occur if a large population exists on the surface of the small intestine. Other symptoms include flatulence, muscle pain, and poor adsorption of food, especially fat. Organism attaches to epithelial cells, but does not penetrate to deeper tissues. Most infections are asymptomatic.
Transmission Typically involves fecally contaminated water or food, but direct fecal-oral route is also possible. Cysts may enter seemingly clear water supplies within the feces of various animals. Infection is frequently spread from one family member to another, and has been a problem in day care centers.
Treatment: Not affected by chlorine; boiling and filtration are necessary.
Giardia lamblia
