2. Definition
Amebiasis is infection with the parasitic
intestinal protozoan Entamoeba histolytica
(the “tissue-lysing ameba”)
Most infections are probably asymptomatic
E. histolytica can cause disease ranging from
dysentery to extraintestinal infections,
including liver abscesses.
4. LIFE CYCLE AND TRANSMISSION
E. histolytica exists in two stages
1) Cyst form
2) Trophozoite form
Infection (of which humans are the natural hosts) is acquired by ingestion of cysts
contained in fecally contaminated food or water or, more rarely, through oral-anal
sexual contact
Cysts survive stomach acidity and excyst within the small intestine
form the 20- to 50-μm trophozoite stage
Trophozoites can live within the large-bowel lumen without causing disease or can
invade the intestinal mucosa, causing amebic colitis
In some cases, E. histolytica trophozoites invade through the mucosa and into the
bloodstream, traveling through the portal circulation
reach the liver and causing amebic liver abscesses
trophozoites may be excreted into the stool and killed by air
Trophozoite cysts within the large bowel are excreted in the stool, continuing the
life cycle
8. Epidemiology
Most cases of amebiasis are due to Entameba dispare and
entameba moshkovskii which are non invassive parasites
90% cases of amebiasis due to Entameba Histolytica are
asymptomatic
10% of cases are symptomatic
prevalence of Amebic liver abscess is 7 time is higher in men than
women
The disease is more common in areas with poor sanitation and
crowding
Mexico, India, tropical regions of africa, south and central of
America and Asia are endemic for disease
Incidence of disease in this regions are 544 cases in100000
papulation
Entamoeba histolytica is the fourth leading cause of mortality due
to parasitic disease in humans. (The first being malaria). Amebiasis
is the cause of an estimated 50,000-100,000 deaths each year.
10. Pathogenesis
Amoebic trophozoites invade the colon causing colitis. They may also invade the
portal circulation and travel to the liver, causing liver abscess.
Gastrointestinal Pathology
The spectrum of colitis in amoebiasis ranges from mucosal thickening, to multiple
cyst formation, to diffuse Inflammation / oedema, to necrosis and perforation of
colonic wall
Binding of E. histolytica to epithelial cells via galactosamin-lectin. This molecule
shows homologous to human CD59, conferring resistance to complement . A
change in the epithelial permeability is induced, probably via the inter-cellular
tight junctions.
Cell lysis and apoptosis of mucosa are thought to be mediated by amoebapores,
peptides capable of forming pores in lipid bi-layers.
Trophozoites invade through to the submucosa causing flask shaped cysts
Cysteine proteinases released by trophozoites digest extracellular matrix in liver
and colon, and induce interleukin-1 mediated inflammation. Proteinases also
cleave IgA and IgG antibodies.
Neutrophils and macrophages are drawn to invasion sites. E. histolytica can lyse
neutrophils leading to further tissue damage, and contributing towards the
induction of diarrhoea
Inflammation is a significant cause of tissue damage, however, innate immunity
may be the main combatant against the disease
11. Pathogenesis
Hepatic Pathology
Trophozoites invading the colonic mucosa may enter the hepatic
circulation and reach the liver
Well circumscribed abscesses are formed in the liver containing liquefied
cells surrounded by inflammatory cells and trophozoites
Adjacent parenchyma is usually unaffected
15. Asymptomatic carriers (non invasive form)
- 90% without symptoms
- does not damage lumen
Invasive forms:
Amoebic colitis
- flask shaped ulcers superficial or deep
- abd pain, diarrhoea, blood, fever
- tenesmus, peri-anal ulcers
Fulminant colitis - <0.5%
- severely ill with high fever
- intestinal bleeding
- perforation
- paralytic ileus
16. Amoeboma
- 1% of cases
- inflammatory thickening of intestinal wall
- palpable mass with trophozoites
Symptoms of amoebic colitis
Symptoms Percentage
1. Diarrhea 100
2. Dysentery 99
3. Abdominal pain 85
4. Fever 68
5. Dehydration 5
6. Length of symptoms 2 to 4 weeks
17. Symptom Bacillary dysentery Amoebic dysentery
Onset Acute Gradual
General
Condition
Poor Normal
Fever High grade Little fever (adult)
Tenesmus Severe Moderate
Dehydration Frequent Little dehydration
(adult)
Faeces No trophozoites Trophozoites present
Culture Positive Negative
18. Extra-intestinal
Amoebic liver abcess
- via portal system
- 5% of invasive disease
- 10 times more common in men
Pleuropulmonary
- direct spread from liver abcess (10%)
- haematogenous spread
Brain
- abrupt onset & rapid progression
- death in 12-72 hrs
21. Complications
• Amoeboma.
(localized granulomatous mass misdiagnosed
with carcinoma)
• Hemorrhage.
• Perforation of ulcer.
(secondary peritonitis --- rare but fatal)
• Stricture of colon.
(secondary to fibrosis)
• Appendicitis.
• Peritonitis
• Pleural Effusion
22. AMEBIASIS
Diagnosis
Fresh stool or colon mucus shows cysts or
trophozoites
Often 3 or more stool exams required
Serologic tests important to distinguish amebiasis
from ulcerative colitis
Sigmoidoscopy useful to inspect ulcers and obtain
stool or mucus for culture & stain
Abd. CT needed if liver abscess suspected
Abdominal Ultrasound
25. Treatment of Specific Forms of Amebiasis
Asymptomatic Intestinal Infection
Asymptomatic carriers are treated with a luminal amebicide.
Standard luminal amebicides are:
Diloxanide furoate, Iodoquinol, and Paromomycin.
Therapy with a luminal amebicide is also required in the
treatment of all other forms of amebiasis.
Amebic Colitis
Metronidazole plus a luminal amebicide is the treatment of
choice for amebic colitis and dysentery.
Tetracyclines and erythromycin are alternative drugs for
moderate colitis but are not effective against
extraintestinal disease.
Dehydroemetine or emetine can also be used, but are best
avoided because of toxicity.
26. Metronidazole & Tinidazole
Metronidazole is the drug of choice in the treatment
of extraluminal amebiasis.
It kills trophozoites but not cysts of E histolytica and
effectively eradicates intestinal and extraintestinal
tissue infections.
Tinidazole, have similar activity and better toxicity
profile than metronidazole.
27. Prevention & Control
Primary prevention
- Safe excreta disposal
- Safe water supply
- Hygiene
- Health education
Secondary
- Early diagnosis
- Treatment
28. Primary prevention
Sanitation Water Food hygiene H edu.
-excreta -protect -protect food -long
-wash hands -sand filter -acetic acid term
-latrines -boiling -detergent
-food handlers
examine
treat
educate