Entamoeba histolytica
Etiology: Infection is established by ingestion of Entamoeba
histolytica cysts which release trophozoites.
Epidemiology
Food or drink contaminated with E.histolytica
cysts and direct fecal-oral contact are the most common means of infection.
Untreated water and human feces used as
fertilizer are important sources of infection.
Food handlers carrying ameThe
pathogenecity of E. histolytica is believed to be dependent on two
mechanisms:
1- Cell contact.
2- Toxin exposure.
· Once the trophozoites invade the
intestinal mucosa, they produce tissue destruction (ulcers)
with little local
inflammatory response.
· The organisms multiply and spread
through the wall underneath the intestinal epithelium to produce flask shaped
ulcers.
· These lesions are commonly seen in the
caecum, transverse colon, and sigmoid colon.
· Amebae may produce similar lytic
lesions if they reach the liver.
· Rarely the infection may extend
extraintestinally to lungs and brain.
biccysts may play a role in spreading
the infection.
Clinical manifestations
1- Intestinal amebiasis
· The onset is usually gradual with
colicky abdominal pain and frequent bowel movements.
· Diarrhea is frequently associated with
tenesmus.
· Stools are blood-stained and contain
fair amount of mucus with few leukocytes.
· The attacks of dysentery are recurrent
in untreated cases.
Complications
a- Ameboma.
b- Toxic megacolon.
c- Extraintestinal extension.
d- Local perforation and peritonitis may
occur.
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