Amoebiasis (Entamoeba Histolytica) - Symptoms and Treatment

Amebiasis is the name of the disease caused by the amoeba Entamoeba histolytica, a protozoan that can cause severe gastrointestinal symptoms such as bloody diarrhea and liver abscess. Amebiasis is an infection that occurs worldwide, but is most common in poor regions and poor sanitation.

Life cycle of Entamoeba histolytica
Life cycle of Entamoeba histolytica

Warning: do not confuse the Entamoeba histolytica with other harmless amoeba like dispar Entamoeba, Entamoeba moshkovskii, Endolimax nails or Entamoeba coli.

How do you get amoebiasis

Intestinal amoebiasis is a disease that occurs when the individual is contaminated with the amoeba Entamoeba histolytica. It is transmitted by the fecal-oral route, or an infected person eliminates the parasite in feces, and another, in some way ends up swallowing it.

This transmission mode can take place in different ways, mainly through consumption of contaminated water or food. The transmission can occur, for example, when a person evacuates not wash their hands properly and will prepare other foods. Bathing or consume local water with poor sanitation are also a risk factor for amebiasis.

People living in the same household of infected patients at high risk of contamination, since the amoeba cysts are very resistant and can contaminate common objects and use them to survive for several days.

Any contact with contaminated feces can cause transmission, including people who have anal intercourse, followed by oral sex.

Life cycle of Entamoeba histolytica

The Entamoeba histolytica eliminated in the stool is in the form of cysts which is highly resistant to hostile environments and can survive in the environment for several months. The ingestion of a single cyst Entamoeba histolytica is enough to contaminate the patient.

The cyst, after being ingested, passes unscathed by the acidity of the stomach, and changes to the trophozoite form to get in the intestines. When they reach the colon, the trophozoites adhere to your wall and start to colonize it. In most cases the Entamoeba histolytica is a commensal behavior, that is, live in harmony with the host, feeding on our food and not producing symptoms.

The trophozoites multiply in the colon binary form and return the form cysts, which are eliminated in the feces. The patient removes the contaminated Entamoeba histolytica in the form of cysts and trophozoites, but only the former are able to survive in the environment. Even if another individual will ingest the trophozoite form, it is unable to cause disease, it is destroyed by stomach acid. Therefore, only the cysts Entamoeba histolytica is capable of causing disease.

Amebiasis disease

In about 90% of cases, the patient becomes infected asymptomatic carrier of amoeba. However, by mechanisms not entirely understood, in a small proportion of infected patients, Entamoeba histolytica may have aggressive behavior, invading the colon wall, destroying epithelial cells and causing large intestinal inflammation, which leads to bloody diarrhea and other symptoms of amebiasis that will be exposed later.

The amoeba can also go through the colon wall and fall into the bloodstream, going to lodge in other organs such as liver, lungs and brain.

We do not know exactly why in a minority of cases amebiasis becomes an aggressive disease but some factors are already clarified, as the stocks of more virulent strains of amoeba and changes in the immune status of the patient.

Among the risk factors for symptomatic amebiasis include:
  • Pregnancy
  • Use of immunosuppressive drugs
  • The use of corticoids
  • Alcoholism
  • Age of extremes (infants and the elderly)
  • HIV
  • Cancer
  • Malnutrition

Symptoms of amebiasis

As already said, more than 90% of patients infected with Entamoeba histolytica no symptoms. When there is symptomatic disease, it usually develops between 1 to 4 weeks after the infection by the parasite cysts.

In 10% of patients with the disease amoeba, the most common symptoms are usually abdominal pain, tenesmus (painful evacuate) and aqueous massive diarrhea with several bowel movements per day, and weight loss. The table is usually more drawn than those of viral gastroenteritis or food poisoning, with symptoms worsening over 1 to 3 weeks. It is not uncommon also be fever and dysentery (bloody diarrhea).

Most cases of amebiasis is mild to moderate intensity, but rarely, in about 0.5% of the cases, the disease can present in fulminant with intestinal necrosis, colonic perforation and severe peritonitis. In these cases, the mortality exceeds 40%.

Amebiasis can also have a chronic form, with recurrent episodes of cramps and bloody stools, a table much like what occurs in the intestine inflammatory diseases such as ulcerative colitis and Crohn's disease.

Amebiasis extraintestinal

The extra-intestinal organ most affected by Entamoeba histolytica is the liver. The most common form of presentation is hepatic abscess, which occurs in up to 5% of patients with symptomatic intestinal amebiasis. The most common symptoms of liver abscess by the amoeba are fever and pain in the liver area (upper right quadrant of the abdomen).

More rarely, the amoeba can also form abscesses in the lungs or brain.

Diagnosis of amebiasis

The diagnosis of infection by Entamoeba histolytica is usually done through the stool test (EPF). As the cysts and trophozoites are not disposed steadily feces, at least 3 samples collected at different days are necessary for diagnosis.

The laboratory will carry out the research needs to be able to distinguish Entamoeba histolytica other amoebas that are morphologically similar but not cause disease in humans, as dispar Entamoeba and Entamoeba moshkovskii.

Serology, which is the detection of antibodies against Entamoeba histolytica, is also an option, being positive in more than 90% of patients with intestinal amebiasis.

Treatment of amebiasis

All infections by the amoeba Entamoeba histolytica should be treated, even in the absence of symptoms, due to the potential risk of future complications and the spread of amoeba to family members.

There are several treatment options for amebiasis. The mild or asymptomatic may be treated with Teclozam. For symptomatic forms, the options are metronidazole, tinidazole or secnidazole.

Infection with Entamoeba dispar or Entamoeba moshkovskii not require treatment. Other amoebae like Endolimax nana and Entamoeba coli does not cause disease and need not be addressed.

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