drug study
classification
amoeba
Amoebiasis is a common infection of the human gastro-intestinal tract. Amoebiasis is
more closely related to poor sanitation and socioeconomic status than to climate. It has
worldwide distribution. It is a major health problem in China, South East and West Asia
and Latin America, especially Mexico.
Amoebiasis is a disease caused by the parasite Entamoeba histolytica. Only about 10%
to 20% of people who are infected with E. histolytica become sick from the infection.
Symptoms
The clinical spectrum ranges from asymptomatic infection, diarrhoea and dysentery to
fulminant colitis and peritonitis as well as extra-intestinal amoebiasis.
Acute amoebiasis can present as diarrhoea or dysentery with frequent, small and often
bloody stools.
Chronic amoebiasis can present with gastrointestinal symptoms plus fatigue, weight
loss and occasional fever.
Extra-intestinal amoebiasis can occur if the parasite spreads to other organs, most
commonly the liver where it causes amoebic liver abscess. Amoebic liver abscess
presents with fever and right upper quadrant abdominal pain.
Other organs can also be involved, including pleuropulmonary, cardiac, cerebral, renal,
genitourinary, peritoneal, and cutaneous sites. In developed countries, amebiasis
primarily affects migrants from and travellers to endemic regions, men who have sex
with men, and immunosuppressed or institutionalized individuals.
Causes
Amoebiasis is caused by parasite Entamoeba histolytica. Several protozoan species in
the genus Entamoeba colonize humans, but not all of them are associated with
disease. It exists in two forms- Vegetative (trophozoite) and cystic forms (cyst).
Trophozoites multiply and encyst in the colon. The cysts are excreted in stool and are
infective to humans. Cysts remain viable and infective for several days in faeces, water,
sewage and soil in the presence of moisture and low temperature.
Transmission occurs via:
Faecal–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 is also recognized especially among
male homosexuals.
Vectors such as flies, cockroaches and rodents can also transmit the infection.
The incubation period for E histolytica infection is commonly 2-4 weeks but may range
from a few days to years.
The use of night soil for agricultural purposes favours the spread of the disease.
Epidemic/ outbreaks (occurrence of more cases of a disease than would be expected in
a community or region during a given time period) are usually associated with sewage
seepage into the water supply.
Diagnosis
Entamoeba histolytica must be differentiated from other intestinal protozoa. Microscopic
identification of cysts and trophozoites in the stool is the common method for
diagnosing E. histolytica. Differentiation is based on morphologic characteristics of the
cysts and trophozoites.
In addition, E. histolytica trophozoites can also be identified in aspirates or biopsy
samples obtained during colonoscopy or surgery.
Immunodiagnosis -Antibody Detection-
a) Enzyme immunoassay (EIA) is most useful in patients with extra-intestinal disease
(i.e., amoebic liver abscess) when organisms are not generally found on stool
examination.
b) Indirect hemagglutination (IHA).
If antibodies are not detectable in patients with an acute presentation of suspected
amoebic liver abscess, a second specimen should be drawn 7-10 days later. If the
second specimen does not show sero-conversion, other tests should be considered.
Detectable E. histolytica-specific antibodies may persist for years after successful
treatment, so the presence of antibodies does not necessarily indicate acute or current
infection.
Antigen Detection-
Antigen detection may be useful as an adjunct to microscopic diagnosis in detecting
parasites and to distinguish between pathogenic and nonpathogenic infections.
Molecular Diagnosis-
Conventional Polymerase chain reaction (PCR)-In reference diagnosis laboratories,
molecular analysis by PCR-based assays is the method of choice for discriminating
between the pathogenic species (E. histolytica) and the nonpathogenic species (E.
dispar).
Radiography, Ultrasonography, Computed tomography (CT) and Magnetic resonance
imaging (MRI) can be used for detection of liver abscess, cerebral amoebiasis.
Rectosigmoidoscopy and colonoscopy can provide diagnostic information in intestinal
amoebiasis.
Management
For symptomatic intestinal infection and extra intestinal disease, treatment with
antiamoebic drugs should be taken with consultation of a physician. Asymptomatic
patients infected with E. histolytica should also be treated with antiamoebic drugs,
because they can infect others and because 4%–10% develop disease within a year if
left untreated.
Liver aspiration- Liver aspiration is indicated only if abscesses are large (> 12 cm),
abscess rupture is imminent, medical therapy has failed, or abscesses are present in
the left lobe.
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
