Biological bases of parasism class Sarcodina

Entamoeba Histalytica

MORPHOLOGY
The trophozoites are 20-30 µm in diameter and contain a vesicular nucleus with a central endosome, peripheral chromatin and radial achromatic fibrils (imparting a 'cart-wheel' appearance). The cysts are spherical measuring 10-15 µm in diameter and have 4 nuclei.

CYST MORPHOLOGY
Cysts are typically found in formed stool, whereas trophozoites are typically found in diarrheal stool. Infection with Entamoeba histolytica (and E.dispar) occurs via ingestion of mature cysts from fecally contaminated food, water, or hands.

LIFE CYCLE
Infection by Entamoeba histolytica occurs by ingestion of mature cysts (2) in fecally contaminated food, water, or hands. Excystation (3) occurs in the small intestine and trophozoites (4) are released, which migrate to the large intestine.

PATHOGENECITY
Entamoeba histolytica, a protozoan parasite, is the etiologic agent of amoebiasis in humans. It exists in two forms—the trophozoite which is the active, dividing form, and the cyst which is dormant and can survive for prolonged periods outside the host. In most infected individuals the trophozoites exist as commensals.

DISEASE
Entamoeba histolytica is an anaerobic parasitic amoebozoan, part of the genus Entamoeba. Predominantly infecting humans and other primates causing amoebiasis, E. histolytica is estimated to infect about 35-50 million people worldwide. E. histolytica infection is estimated to kill more than 55,000 people each year.

DIAGNOSIS
A single stool examination has a low sensitivity of detecting the parasite . The best diagnostic method is detection of E. histolytica antigen or DNA in stool . Clinical diagnosis of amebiasis is difficult because of the nonspecific nature of symptoms

TREATMENT
To treat invasive amebiasis, metronidazole (Flagyl, MetroGel, Noritate) is recommended even for amoebic liver abscesses (up to 10 cm sized abscesses). Tinidazole (Tindamax) is FDA approved for treatment of both intestinal or extraintestinal (invasive) amebiasis.

PREVENTION and CONTROL
Improved sanitation will help to reduce the liklihood of transmission. Travelers to endemic areas can reduce the risk of infection by drinking bottled water, not using ice cubes in drinks, and washing fruits and vegetables with clean water (or by peeling them yourself).