Protozoa - Giardia duodenalis: Giardiasis
Giardiasis
Signs/Symptoms:
Approximately half of infected people are asymptomatic.
When symptomatic, intestinal illness ranges from mild diarrhea to severe malabsorption
Giardiasis produces watery or fatty foul-smelling diarrhea with bloating and flatulence; however, unlike amebiasis, bloody stools are rare because the causative parasites are not invasive.
Extra-intestinal spread is rare (unlike amebiasis).
Post-giardiasis complications are reported, including lactose intolerance and irritable bowel syndrome.
Morphology & pathogenesis:
Giardia duodenalis trophozoites have a pear-shaped body, with flagella.
Two nuclei, and, surrounding them, the large adhesive disk (aka, ventral disk).
The disk facilitates firm adhesion to the villi of the small intestine.
Giardiasis pathogenesis is similar to amebiasis; we'll highlight some key exceptions.
The parasites damage the enterocytes, leading to diarrhea and inhibition of nutrient absorption.
Because the parasites are rarely invasive, giardiasis is not typically associated with bloody stools.
Chronic giardiasis can lead to developmental impairment; this a major concern in developing countries, for example, where the effects of giardiasis exacerbate existing malnutrition.
Images:
CDC / Janice Haney Carr - http://phil.cdc.gov/PHIL_Images/8698/8698_lores.jpg
Dr. Stan Erlandsen (1988). Public Health Image Library (PHIL) -- image #11632