AMOEBIASIS PATHOPHYSIOLOGY
Ingestion of bacteria
Trophozoite colonization in mucosa
Endotoxin production affecting the linings of the small
intestines, colon and capillary
Necrosis of the mucosal layer
Ulceration
Gangrene
Toxaemia
We can get amoebic cyst through the ingestion of contaminated water or food , we can also get
this from fecal oral route. When cyst is swallowed, it passes through the stomach unharmed
and shows no activity while in an acidic environment. When it reaches the alkaline medium of
the intestine, the metacyst begins to move within the cyst wall, which rapidly weakens and
tears. The quadrinucleate amoeba emerges and divides into amebulas that are swept down
into the cecum. This is the first opportunity of the organism to colonize, and its success
depends on one or more metacystic trophozoites making contact with the mucosa.
Mature cyst in the large intestines leaves the host in great numbers (the host remains
asymptomatic). The cyst can remain viable and infective in moist and cool environment for at
least 12 days, and in water for 30 days. The cysts are resistant to levels of chlorine normally
used for water purification. They are rapidly killed by purification, desiccation and temperatures
below 5 and above 40 degrees.
The metacystic trophozoites of their progenies reach the cecum and those that come in contact
with the oral mucosa penetrate or invade the epithelium by lytic digestion. The trophozoites
burrow deeper with tendency to spread laterally or continue the lysis of cells until they reach
the sub-mucosa forming flash-shape ulcers. There may be several points of penetration. From
the primary site of invasion, secondary lesions maybe produced at the lower level of the large
intestine. Progenies of the initial colonies are squeezed out to the lower portion of the bowel
and thus, have the opportunity to invade and produce additional ulcers. Eventually, the whole
colon may be involved.
E. histolytica has been demonstrated in practically every soft organ of the body. Trophozoites
which reach the muscularis mucosa frequently erode the lymphatics or walls of the mesenteric
venules in the floor of the ulcers, and are carried to the intrahepatic portal vein. If thrombi occur
in the small branches of the portal veins, the trophozoites in thrombi cause lytic necrosis on the
wall of the vessels and digest a pathway into the lobules.
The colonies increase in size and develop into abscess.
A typical liver abscess develops and consists of:
Central zone necrosis
Median zone of stoma only
An outer zone of normal tissue newly invaded by amoeba. Most amoebic abscess of the
liver are in the right lobe.
Next to the liver, the organ which is the frequent site of extra-intestinal amoebiasis is the lungs.
This commonly develops as an extension of the hepatic abscess.
AMOEBIASIS
Signs and Symptoms
diarrhea (which may be bloody)
stomach pains
cramping
nausea
loss of appetite
fever
Complications
Complications of amoebic colitis include the following:
Fulminant or necrotizing colitis
Toxic megacolon
Amoeboma
Recto vaginal fistula
Complications of amoebic liver abscess include the following:
Intraperitoneal, intrathoracic, or intrapericardial rupture, with or without secondary bacterial
infection
Direct extension to pleura or pericardium
Dissemination and formation of brain abscess
Other complications due to amoebiasis include the following:
Bowel perforation
Gastrointestinal bleeding
Stricture formation
Intussusception
Peritonitis
Empyema
