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Giardia lamblia; Giardia intestinalis
Etiologic agent of giardiasis.
Epidemiology:
1) both endemic & epidemic infections worldwide
2) especially in travelers, campers, children & workers in day care centers & homosexual men
3) infectious cysts live in the environment
4) trophozyte attaches to the small intestine; responsible for symptoms in inected individuals
5) infection generally occurs via drinking contaminated water
6) Giardia is not killed by usual concentrations of chlorine in murine municipal water
7) water supply must be filtered to eliminate Giardia
8) campers must boil water from streams or lakes in endemic areas
Pathology:
1) etiologic agent of giardiasis
2) trophozoites multiply in the small bowel & attach to the mucosa by a ventral concave sucking disc
3) disruption of the brush border
4) disaccharidase deficiency
Laboratory:
1) Giardia lamblia antigen
2) Giardia lamblia serology
3) Giardia lamblia DNA
4) Giardia lamblia 18S rRNA
5) light microscopy of stool specimen
a) trophozoites
- are predominant in watery feces
- direct mounts are helpful for demonstrating trophozoites
- may be seen on permanently stained slides
- pear-shaped with tapered posterior end
- two nuclei that give the appearance of a smiling face with prominent eyes
- sucking disc on ventral surface
- 4 lateral, 2 ventral & 2 caudal flagella are generally not visualized on wet mounts or stained specimens
- measure 12-15 by 9-10 um (range 10-20 um in length)
b) cysts
- are more likely to be found in formed stools
- may be seen in direct mounts or with concentration techniques
- may be seen on permanently stained slides
- oval & generally with 4 nuclei
- dark-staining median bodies that cross longitudinal fibrils
- cytoplasm often retracted from cyst wall
6) Giardia lamblia stool culture
7) also see giardiasis
Related
giardiasis (beaver fever)
General
Giardia
Properties
KINGDOM: animal
PHYLUM: protozoa
References
- Clinical Diagnosis & Management by Laboratory Methods,
19th edition, J.B. Henry (ed), W.B. Saunders Co., Philadelphia,
PA. 1996, pg 1277-78
- http://www.biosci.ohio-state.edu/~parasite/giardia.html
- Medical Knowledge Self Assessment Program (MKSAP) 14, 15, 18
American College of Physicians, Philadelphia 2006, 2009, 2018
- Grimm L
What's Eating You: 12 Common Intestinal Parasites.
Medscape. November 25, 2019
https://reference.medscape.com/slideshow/intestinal-parasites-6010996