Curriculum · Public Health and Communicable Diseases
Giardiasis
What it is
Giardia lamblia is a microscopic protozoan parasite that is not visible on gross examination. That sets it apart from the worms that can be seen: Ascaris lumbricoides is a large roundworm that typically infects the ileum, tapeworms are flat and segmental and are found in the stool as segments called proglottids, and hookworms are round and typically 6-12 mm in length.
Its weight lies in chronic diarrhea, which is defined as lasting longer than 4 weeks. Except for Giardia lamblia, infectious causes of chronic diarrhea are uncommon in immunocompetent adults in developed countries.
Causes and risk
Giardia lamblia and cryptosporidiosis are acquired from contaminated water sources, such as fresh water found on a camping trip. Infection with Giardia lamblia should be considered in patients exposed to young children, for example daycare units, or to potentially contaminated water such as lakes and streams.
The host matters as well. Selective IgA deficiency, the most common 1° immunodeficiency, carries an increased susceptibility to giardiasis; its findings are low IgA with normal IgG and IgM levels, and the majority are asymptomatic although airway and GI infections, autoimmune disease and atopy can be seen.