What is it?
It´s an infection by a parasite or protozoon that affects humans and can be restricted to the intestine, having diarrhea as its main symptom or causing fever and different symptoms depending on the “invaded” organ.
More often, the usual organ to be compromised is the liver. The causative agent is the Entamoeba hystolitica. This parasite infects approximately 1% of the world population, principally the poor population of developing countries. Recently, a parasite that resembles the Entamoeba hystolitica and that doesn´t cause the disease has been identified (Entamoeba dispar).
This is important because finding the amoeba in the feces of an individual doesn´t necessarily characterize amebiasis. The E. dispar doesn´t cause the disease, while the E. hystolica may be present in the individual without causing the disease either. The differentiation between both is made through laboratory tests, and seldom is shown to be relevant.
How is it acquired?
By ingesting food or water contaminated with fecal stuff containing Entamoeba cysts. It can be acquired by other means, but these are less frequent and are virtually restricted to individuals with compromised immunity.
What does one experience?
The symptoms of people with amebiasis range from diarrhea with gripes and increase in intestinal sounds to more intense diarrhea with blood loss in the feces, fever and weight loss. In these cases an invasion of the large intestine wall occurs with more intense inflammation, which is called colitis by the doctors. Ulcerations may occur on the internal lining of the large intestine, which accounts for the bleeding. Rarely does the infection cause intestinal perforation, when it occurs, the manifestation is one of a severe abdominal disease with intensive pain, rigidity and increase in wall sensitivity, in addition to outmost prostration of the affected individual. The disease may present in a milder way, with intermittent diarrhea, it taking many years for a generalized impairment to take place.
Not very commonly can the protozoon penetrate the bloodstream and form abscesses (accumulation within an organ or body structure) in the liver that cause pain and fever with chills. These abscesses can disrupt into the abdomen or even the chest, compromising the pleura (layer that lines the lungs) or the pericardium (layer that lines the heart). Also, in rare cases, tumors can form in the intestine. These tumors are called “ amebomas”.
The situations of extraintestinal or invasive disease are the ones that lead to more severe cases that evolve to the death of the infected individual.
How is the diagnosis made?
The stool test detects the parasite with some easiness. The most invasive type depends on what the physicians call imaging exams (computerized tomography, echography, or magnetic resonance).
A few times, for diagnostic confirmation, in addition to the imaging exam the doctors uses thin needles to punch the abscesses. In the more invasive types, when the diagnosis cannot be made by identifying the cyst, blood tests are used to detect the presence of antibodies to the parasite.
How to treat it?
The drug most widely used by the physicians is an antimicrobial by the name of metronidazol, but there are other ones whose use is recommended for specific circumstances. The duration of treatment can vary according to how much compromised the person is. At times, when there´s formation of liver abscesses, it may be necessary to aspirate these with a needle for diagnosis or treatment; very rarely will these cases entail surgery.
How to prevent it?
Fecal contamination of the food and water is the chief cause of such infection. As in most intestinal parasitoses, measures of basic sanitation such as water treatment and sewers are decisive in the prevention of this disease.
The most frequently contaminated foods are vegetables cultivated close to the ground. The hygiene of these raw foods must be rigorous, using potent detergents followed by immersion into vinegar or acetic acid solution for 10 to 15 min. The water is rendered totally free of these protozoa only after being boiled.
The suitable treatment of these patients helps eliminate sources of dissemination of the disease, especially in the rural area, where treated water isn´t always available.
General hygiene habits such as washing the hands after using the lavatory are educational procedures that certainly contribute for prevention. The supervision of the food industry by the sanitary surveillance is of paramount importance.
Recently, the likelihood of a vaccine for the not so distant future has shown to be viable.