What is amoebiasis?

Amoebiasis is a protozoan invasion of a person, accompanied by a defeat of the large intestine and capable of generalization.

Amoebiasis is a disease caused by pathogenic strains of Entamoeba histolytica, which are widespread in the world, mainly in countries of the tropical and subtropical climate. The low level of sanitation characteristic for these areas causes a high incidence of amoebiasis. Currently, amebiasis is one of the largest medical and social problems in the population of developing countries and is one of the most frequent causes of death in parasitic bowel diseases. After malaria, this infection ranks second in the world in the frequency of deaths in parasitic diseases. About 480 million people in the world are carriers of E. hystolytica, 48 million of them develop colitis and extraintestinal abscesses, and 40,100 to 100,000 people become lethal. Migration, the deterioration of the economic situation of a number of developing countries, and a low level of sanitation contribute to the spread of amoebiasis and, accordingly, to an increase in the incidence rate.

What provokes / Causes of Amoebiasis:

The causative agent of amebiasis is histolytic, or dysentery, amoeba - Entamoeba histolityca (Losch, 1875; Schaudinn, 1903). Inhabits the large intestine. In addition to the pathogenic E. histolytica, nonpathogenic amoebae are also detected in the human colon: Entamoeba dispar, Entamoeba hartmanni, Entamoeba coli, Endolimax nana, lodamoeba biletschlii, Dientamoeba fragilis. The causative agent belongs to the realm of Animalia, the sub-kingdom of Protozoa, the Sarcomas tigophora, the subtype of Sarcodina.

In the life cycle of histological amoeba there are vegetative (trophozoite), and cystic stages). Unlike other types of amoeba, four forms of vegetative stage are distinguished in dysenteric amoeba: tissue, E. histolytica forma magna, luminal - E. histolytica forma minuta, and pre-cystic.

The tissue form has dimensions of 20-25 μm. Two layers are distinguished in the cytoplasm: ectoplasm and endoplasm. In a fresh preparation, the endoplasm is homogeneous, it does not contain inclusions. In the native preparation, the method of movement with the help of ectoplasmic pseudopodia arising in the form of rapid tremors is well defined. Tissue form of amoeba is found only in acute amebiasis directly in the affected tissue, in feces rarely.

E. histolytica forma magna (erythrophage) is capable of phagocytizing erythrocytes, secreting enzymes, penetrating the mucosa and submucosa of the intestine, causing necrosis and ulceration. The dimensions of the large vegetative form are 20-40 μm, when stretched to 60 - 80 μm, the cytoplasm is also divided into a light ectoplasm free of inclusions and a fine-grained endoplasm in which a subtle nucleus is located. In native smears, the tissue form is actively mobile. Movement is carried out by a relatively rapid, sudden ejection of light transparent ectoplasmic pseudopodia. In the pseudopodia formed, the endoplasm with the erythrocytes contained in it is vortex-like. The pseudopodia is smoothed out and disappears. Then a new pseudopodium is formed on this or in another place of the cell surface, the cytoplasm is transfused and the amoeba moves in a certain direction. Sometimes two pseudopodia are formed at once. One of them gradually increases, and the second disappears.

At the same time there are separate individuals with little mobility. When the preparation is cooled, the mobility of the amoebae is first slowed down, then the body is rounded and they all become immovable. The swallowed red blood cells in native smears are located in the endoplasm and have a yellowish tinge. On preparations stained with iron hematoxylin, the ectoplasm is clear, transparent, and the endoplasma is monophonic, fine-grained, and darker in color. The core has a gentle shell with small grains of peripheral chromatin and a centrally located point karyosome. In the endoplasma are black-colored erythrocytes, the size of which and the intensity of the color depend on the stage of their digestion. A large vegetative form is found in feces in acute amoebiasis.

The enlightened form is a commensal, lives in the lumen of the large intestine, feeds on detritus and bacteria. It is found in people who have experienced acute form of intestinal amebiasis, with chronic recurrent amoebiasis, and with asymptomatic amoeba. The enlightenment form differs from the tissue by the sluggish movement. Its size is from 15 to 25 μm. In the native smears in the luminal form, the division into ecto- and endoplasm is not observed. The structure of the nucleus is the same as that of the tissue form.

The precessional stage (pre-cyst) is a transitional form of the histological amoeba from the luminal to the cyst. Its size is 10-18 microns. The division into ecto- and endoplasm is not noticeable. The swallowed bacteria, erythrocytes and other cellular elements do not contain. All forms of the vegetative stage of E. histolytica quickly die in the external environment.

Cysts are a resting stage of development of histological amoeba, which ensures the preservation of the species in the external environment. On uncolored preparations, cysts are rounded, colorless formations with a two-contour shell, with a diameter of 10 to 15 μm (an average of 12 μm). Mature cysts contain 4 cores. On preparations stained with iron hematoxylin, cytoplasm of gray color. It defines from 1 to 4 nuclei with sickle-shaped chromatin grains located on the inner shell and a centrally located point karyosome. In the cytoplasm of immature cysts, the glycogen vacuole is clearly contiguous in the form of a light spot and rod-shaped chro- matoid bodies with rounded ends are of black color, the sizes and number of which in individual cysts may be different. Chromatoid inclusions are found in 10 - 50% of histone amoeba cysts. Cysts are found in feces of convalescents and cysticans.

Using the method of isoenzyme analysis in the species E. histolytica, pathogenic and non-pathogenic strains of dysentery amoeba have been identified. The rate of movement of pathogenic strains of histolytic amoeba is higher than that of nonpathogenic strains. Trophozoites and cysts of nonpathogenic amoebae differ from similar stages of histological amoeba in size, shape, amount, structure of nuclei, nature of motion and inclusions, etc. Trophozoites of nonpathogenic amoebae feed on bacteria, fungi, cell debris, and erythrocytes are not phagocytosed. Knowledge of the morphological features of nonpathogenic amoebae is necessary for a differential diagnostic diagnosis of the species of these protozoa. The sizes of trophozoites of nonpathogenic amoebas are as follows: E. coli - 30 - 45 μm, Jod. Btitschlii 5-20 μm, End. Nana-5-12 μm; Cysts, respectively, 14-20 microns, 6-16 microns, 5-9 microns. The results of molecular biological studies show that non-pathogenic E. dispar in morphology is a double of E. histolytica, they can only be distinguished by DNA analysis (S. D. Huston et al., 1999).


Amoebiasis is anthroponosis of protozoal etiology. The source of infection in amebiasis is a person who secretes cysts of E. histolytica with feces. The mechanism of transmission is fecal-oral. The intensity of cyst excretion per day ranges from 3 thousand to 3888 thousand in 1 g of feces and on average is 580 thousand. One chronic clinically healthy carrier can daily excrete with feces tens of millions of cysts. Vegetative forms of histological amoeba retain viability in feces no more than 15 - 30 minutes. Cystic forms have considerable resistance in the external environment, their survival depends on the temperature and the relative humidity of the air. In feces at a temperature of +10 ... +20 ° C they remain alive from 3 to 30 days, and at -1 ... -21 ° C - from 17 to 111 days. In the water of natural reservoirs, they survive 9-60 days at a temperature of 10 - 30 ° C, in tap water - up to 30 days, in sewage water - up to 130 days; On the surface of the soil at a temperature of +10 ... + 50 ° С - 2 - 11 days, in deep layers - up to 1 month. On the skin of the hands, the cysts retain their viability up to 5 minutes. In the subungual spaces - 46 - 60 minutes, in the intestines of house flies - up to 48 hours, in milk and dairy products at room temperature - up to 15 days. At a temperature of +2 ... + 6 ° C and a relative air humidity of 80-100% E. histolytica cysts survive on objects of glass, metals, polymers and other materials for 11-25 days, and at a temperature of +18 ... + 27 ° С and relative humidity of air 40 - 65% - no more than 7 hours.

Considering the significant intensity of cysts in amoebiasis, long periods of their survival on environmental objects and food products, factors of amebiasis transmission can be soil, sewage, open water, household and industrial furnishings, fruits, vegetables, food, hands contaminated Cysts of dysentery amoeba.

Symptoms of Amoebiasis

According to the WHO classification, asymptomatic and manifest amoebiasis is distinguished, including intestinal (amoebic dysentery and dysentery amoebic colitis) and extraintestinal (hepatic: acute neural and abscess of the liver, pulmonary and other extraintestinal lesions).

Amoebic dysentery (dysentery colitis) - the main and most frequent clinical form of the disease - can occur acutely and chronically, in severe, moderate and mild forms. The incubation period is from 1 to 2 weeks to 3 to 4 months or more. The main clinical signs of the disease are frequent stools: in the initial period up to 4-6 times a day abundant feces with mucus, then up to 10-20 times a day with blood and mucus with a loss of fecal character. Exercises get the appearance of "crimson jelly". Disease, as a rule, develops gradually, without the phenomena of the general intoxication, body temperature normal or subfebrile. In severe infestation, fever and pulling or cramping pain in the lower abdomen can be noted, which intensify during defecation. Appearing painful tenesmus.

In severe colitis, there are signs of intoxication, which is manifested by an increase in temperature (usually of an abnormal nature), a decrease in appetite, the appearance of nausea, and sometimes vomiting. The abdomen in the acute period is mild, painful in the course of the colon.

With endoscopy (sigmoidoscopy, fibrocolonoscopy) inflammatory changes in the area of ​​the rectum and sigmoid colon are detected in the initial period in 42% of patients. On the 2nd - 3rd day of the onset of the disease against the background of the normal mucosa, areas of hyperemia (2-5 mm in diameter) are noted, somewhat elevating above the level of unchanged intestine parts. From the 4th to the 5th day of the disease, small nodules and ulcers (up to 5 mm in diameter) are identified on the site of these areas of hyperemia, of which yellowish curds are secreted when pressed. There is a small zone of hyperemia around the ulcers. From the 6th to the 14th day of the disease, ulcers up to 20 mm in size with pitted edges and filled with necrotic masses are detected. Thus, changes in the intestinal mucosa that are typical of amoebiasis are formed during the first 2 weeks of the disease. With a rapidly progressing course, such changes are detected already on the 6th-8th day of the disease.

The acute process lasts no more than 4-6 weeks, then there comes a remission lasting from several weeks to 1 or more months. After remission, the disease resumes and acquires a chronic form, which can last for years without specific treatment.

Diagnosis of Amebiasis

The diagnosis of amebiasis is established on the basis of epidemiological history, clinical picture of the disease and laboratory test results.

The results of a parasitological study are decisive for the diagnosis. The parasitological diagnosis of amoebiasis is posed when a tissue and a large vegetative form are found in the material under study, trophozoites-erythrophages. The material for the study can be: feces, rectal smears selected with sigmoidoscopy, biopsy material of ulcerative lesions, aspirate of the contents of liver abscess, the tissue forms being localized mainly in the outer walls of the abscess, and not in the necrotic masses located in the center.

From the first day of illness, microscopy of native smears from freshly isolated feces in physiological saline and smears stained with Lugol's solution is carried out. In acute and subacute course of the disease, the vegetative tissue form of amoeba is sought, and in convalescent and asymptomatic carriers - a small luminal shape and cyst. You can also prepare permanent preparations stained with hematoxylin according to Heidenhain. Identification of only luminal forms and cysts of amoebas in feces is not enough for the final diagnosis.

To increase the effectiveness of parasitological studies, a multiple (up to 3-6 times) study of freshly isolated feces (no later than 10-15 minutes after defecation) and other biological substrates is used, collecting the material in preserving fluids for long-term storage of the preparation, and methods of enrichment.

In the presence of clinical signs of intestinal amebiasis and negative results of parasitological studies, serological reactions based on the detection of specific anti-amoebic antibodies are used. RIF, RSK, ELISA, hemagglutination inhibition and neutralization with paired sera are used (antibodies titer increase 4 and more times). Serological tests are positive in 75% of patients with intestinal amoebiasis and 95% of patients with extraintestinal amoebiasis.

For the diagnosis of extraintestinal amoebiasis, in addition to immunological, a comprehensive instrumental examination is performed: ultrasound, X-ray examination, computed tomography and other methods that can determine the localization, size and number of abscesses, and monitor the results of treatment.

From modern methods of investigation, the detection of antigens of dysenteric amoebas in feces and other material using monoclonal antibodies is used; Determination of parasitic DNA by PCR.

Treatment of Amoebiasis

In general, all drugs used to treat amebiasis can be divided into 2 groups: "contact" or "luminal" (affecting the intestinal luminal forms) and systemic tissue amoebicides.

Luminal amoebicides are used to treat noninvasive amoebiasis (asymptomatic "carriers"). Enlightened amoebicides are also recommended after the end of treatment with tissue amoebicides for the elimination of amoebas left in the intestine, in order to prevent relapses. In particular, there are observations on the development of amoebic liver abscesses in persons with intestinal amebiasis, who received only tissue amoebicides without the subsequent appointment of luminal amoebicides. In particular, the recurrence of amoebic liver abscess in a patient 17 years after successfully cured a newly discovered liver abscess is described.

In conditions where it is impossible to prevent re-infection, the use of luminal amoebicides is not appropriate. In these situations, it is recommended that luminal amoebicides be given only for epidemiological reasons, for example to persons whose professional activities may contribute to the infection of others, in particular to food service employees.