Amebiasis is another name for amoebic dysentry, caused by the protozoan Entamoeba histolytica.
Entamoeba histolytica is a parasitic amoeba which lives in the gut and is passed on by swallowing cysts which have been excreted in feces. Once ingested, the cysts (which are unaffected by stomach acid) pass through the stomach to the intestine where they develop into the characteristic unicellular organisms which can be identified by microscopic examination.
Ambeiasis is a problem throughout the world, but is most common in areas with poor sanitation, such as parts of Africa, Latin America, India, and Southeast Asia. Up to 4% of people in the USA are thought to carry the parasite, many of these are immigrants or homosexuals. It has been estimated that out of the 480 million people carrying Entamoebae worldwide, only 50 million of these will show any symptoms of dysentry, although it is responsible for up to 110,000 deaths per year.
If the range of symptoms suggest amebiasis, microscopic examination of the stools is the usual method of identification. However, presence of amoebae in the stool does not always indicate Entamoeba histolytica
infection because there is another species, Entamoeba dispar
, which is far more common and never causes disease. Blood tests are the only way to make an accurate diagnosis.
Amoebic liver abscesses can be detected using CT scans, and ultrasonography, along with serological testing to prove that Entamoeba histolytica is responsible. Effective treatment of this type of infection is crucial because mortality rates are otherwise very high.
Most infections are asymptomatic - symptoms are only produced in about 1:10 cases when the amoebae invade the intestinal wall, rather than just residing in the gut lumen. Where symptoms do occur, they begin within 1 - 4 weeks of ingestion of contaminated food or water and include:-
- Mild to severe diarrhea (which may be bloody) sometimes resulting in dehydration
- Stomach pain and abdominal cramping
- Fever and chills
- On rare occasions the amoebae may pass through the intestinal wall invading the body and causing abscesses in the liver, lungs or brain
- Drink bottled, or boiled water in areas where amebic dysentry is common. Never drink from public water fountains etc.
- Avoid ice cubes in drinks
- Avoid unpasteurised milk and cheese
- Only eat fruit or vegetables which you have peeled yourself
- Avoid eating food from street vendors
- Follow a high standard of personal hygiene - thoroughly wash hands with soap
and water after using the toilet, after changing diapers, and before handling food
There are two different types of drug treatments, one which clears the organism from the gut lumen, and the other which eliminates it from the tissues.
A cure is usually effected within 3 weeks of starting drug therapy but microscopic examination of stool samples should continue for several months just to make sure there are no parasites remaining.