Useful For

Diagnosis of intestinal amebiasis, colitis and rectocolitis. Differential diagnosis of dysentery.

Reflex Tests

Testing Algorithm

Stool specimens submitted in preservative are subjected to microscopy employing iodine wet mount and Trichrome stain for detection of Entamoeba histolitica and other intestinal parasites.

Indications for Testing

Colitis, rectocolitis and dysentery.

Special Instructions and Forms

Entamoeba histolytica infection is a Provincial Notifiable Disease. More Provincial information can be obtained from LINK

Clinical Information

The clinical spectrum of intestinal E. histolytica infection ranges from an asymptomatic carrier state and acute colitis to fulminant colitis with perforation, depending on the host’s nutritional status and susceptibility, including age and virulence of infecting strain.

Invasive intestinal amebiasis usually manifests as an acute rectocolitis. Most patients present with a nontoxic dysenteric syndrome, and constitutional symptoms are not as prominent as in Shigella dysentery. The onset of acute rectocolitis is gradual and 85% of patients have intense abdominal pain. Initially there are loose watery stools, but these rapidly become blood-stained and contain mucus. Tenesmus occurs in 50% of patients and is always associated with rectosigmoidal involvement. Watery diarrhea or loose stools without blood may be present for a few days, particularly if the distal colon is involved.

Entamoeba histolytica and Giardia lamblia infections are two of the most common protozoal infections seen worldwide. The infection is acquired by ingestion of cysts in fecally contaminated food or water, or sexually (particularly in men who have sex with men). Excystation and infection occur in the large intestine from where trophozoites attach to the intestinal wall and liberate extracellular enzymes which enable invasion of the mucosa and facilitates spread to other organs, especially the liver and lung where abscesses develop. Diagnosis of invasive amebiasis, in particular amebic liver abscess, is supported by E. histolytica-specific serology.

Reference Values

NO OVA CYSTS AND PARASITES DETECTED

Interpretation

E. histolytica (pathogenic), E. dispar (nonpathogenic) and E. moshkovskii (nonpathogenic) may be indistinguishable by microscopy. In addition, asymptomatic E. histolytica often occur, complicating interpretation of microscopic findings. On occasion, ingested red blood cells may be detectable in E. histolytica (only) aiding definitive identification of pathogenic E. histolytica.

References

Leber, A. L., and Novak-Weekley, S. 2007. Intestinal and Urogenital Amebae, Flagellates, and Ciliates, p. 2092-2112. In Murray, P. R., Baron, E. J., Jorgensen, J. H., Landry, M. L., and Pfaller, M. A. Manual of Clinical Microbiology, 9^th ed., vol. 2. ASM Press, American Society for Microbiology, Washington, DC.

Petri, Jr., W. A., and Haque, R. 2010. Entamoeba Species, Including Amebiasis, p. 3411-3425. In Mandell, D., Bennett, J. E., and Dolin, R. Principles and practice of infectious diseases, 7^th ed., vol. 2. Churchill Livingstone, Elsevier, Philadelphia, PA.

Martínez-Palomo, A. and Espinosa-Cantellano M. 1999. Amebiasis and other protozoan infections, 6.25.1 – 6.25.4. In Armstrong, D. and Cohen, J. Infectious Diseases, vol. 2. Mosby, Harcourt Publishers Ltd.