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Amoebiasis is a protozoan infection of the intestinal mucous membrane usually of the colon caused by a protozoan known as Entamoeba histolytica.
The disease is found in all parts of the world but more common where sanitary conditions are poor and in areas of low socioeconomic status. Amoebiasis can occur in families or spread through institutions but usually does not occur in epidemics.
Amoebiasis can be endemic in a population in which many individuals are asymptomatic cyst-passers with only a few getting the disease.
Although this parasite can affect some people, of the, affected only about 10 to 20% develop the disease.
Like we have mentioned, amoebiasis is caused by parasite Entamoeba histolytica. Several protozoan species in the genus Entamoeba colonize humans, but not all of them are associated with the disease.
Entamoeba hystolytica exists in two forms- Vegetative (trophozoite) and cystic forms (cyst).
Trophozoites multiply and encyst in the colon. The Entamoeba cysts are excreted in stool and are infective to humans. Entamoeba cysts remain viable and infective for several days in fecal matter, water, sewage, and moist soil at low temperatures.
Its transmission occurs via:
The fecal-oral route, either directly by person-to-person contact or indirectly by eating or drinking faecally contaminated food or water.
Sexual transmission by oral-rectal contact among male homosexuals.
Transmission by Vectors such as flies, rodents, and cockroaches.
Amoebiasis can occasionally spread from the bowels to other organs of the body, especially to the liver
leading to amoebic liver disease.
Entamoeba histolytica infection has an incubation period of 2-4 weeks but may range from a few days to years.
The use of night soil for agriculture also favors the spread of amebiasis. Outbreaks are usually associated with seepage of sewage into the water supply.
Once the cysts are ingested, the emerging trophozoites take up residence in the intestinal mucosa.
The organisms multiply in the mucosa (causing the formation of bottle-shaped ulcers each 1- 2cm in diameter).
Too many such ulcers may cover the large intestine. Some of the ulcers may become perforated leading to severe peritonitis with shock.
In the small intestines, the Entamoeba histolytica may pass through the mucous membrane and enter the liver. After a variable incubation period, a liver abscess may form.
The signs and symptoms of amoebiasis can range from asymptomatic to peritonitis.
A patient with acute amoebiasis can present as diarrhea or dysentery with frequent, small and often bloody stools.
Patients with chronic amoebiasis present with GI symptoms, fatigue, weight loss, and occasional fever.
Extra-intestinal amoebiasis occurs in case the parasite spreads to other organs apart from the intestines, most commonly the liver causing an amoebic liver abscess that will present with fever and right upper quadrant abdominal pain.
The most common site for extra-intestinal amoebiasis in the liver where it forms a liver abscess. Other secondary sites include lungs and skin leading to:
Stool for microscopy will indicate trophozoites with ingested red blood cells and cysts of Entamoeba histolytica in amoebic dysentery. Differentiation from other intestinal protozoa is also made possible by morphological features of the trophozoites and cysts.
Radiography, Ultrasound, CT Scan, and MRI can be used for the detection of liver abscess and cerebral amoebiasis.
Full haemogram which may indicate mild anemia and, leucocytosis without eosinophilia,
The erythrocyte sedimentation rate is elevated.
Liver ultrasound scan in case of amoebic liver abscess.
Needle aspiration for microscopy in amoebic liver abscess.
Immunodiagnosis -Antibody Detection is also possible for its diagnosis-
a) Enzyme-Linked Immunoassay (ELISA) is most useful in patients with amoebic liver abscess when organisms are not generally found on stool examination. It measures serum antilectin antibodies (immunoglobulin G).
b) Indirect hemagglutination (IHA) is more useful if antibodies are not detectable in patients with an acute presentation of suspected amoebic liver abscess, a second specimen is drawn 7-10 days later. If the second specimen does not show seroconversion, other tests should be considered.
Detectable Entamoeba histolytica-specific antibodies can persist for a number of years after successful treatment, therefore the presence of antibodies does not necessarily indicate an acute or current infection.
Antigen detection tests may be used as an adjunct to microscopic diagnosis to detect the parasites and distinguish between pathogenic and nonpathogenic amebic infections.
Molecular Diagnosis for example;
Polymerase chain reaction (PCR) is the method of choice for discriminating between the pathogenic species like Entamoeba histolytica and the nonpathogenic species such as Entamoeba dispar and E.moshkovskii.
Immunofluorescent assay (IFA) is a rapid, reliable and producible.
Colonoscopy and rectosigmoidoscopy. Entamoeba histolytica trophozoites can also be identified in aspirates or biopsy samples obtained during colonoscopy or surgery.
Treatment is unnecessary for asymptomatic patients as in time they clear the infection.
Prevention is effected by providing safe drinking water and sanitary disposal of fecal matter.
Regular examination of food handlers and appropriate treatment of the carriers when necessary can also prevent the spread.
Complications arising as a result of amoebic colitis include:
Complications of an amoebic liver abscess include:
Other complications include: