Amoebiasis is a parasitic disease caused by a histolytic amoeba and occurring with intestinal and extra-intestinal manifestations. Intestinal amoebiasis is characterized by copious mucous stools with an admixture of blood, abdominal pain, tenesmus, weight loss, anemia; extra-intestinal – the formation of liver abscess, lungs, brain, etc. The diagnosis of amoebiasis is based on the data of the clinical picture, rectoromanoscopy, colonoscopy, microscopy of smears of the contents of abscesses, serological examination, radiography. In the treatment of amoebiasis, medications (lumen and systemic tissue amoebocides, antibiotics), surgical methods (opening and drainage of abscesses, intestinal resection) are used.
Amoebiasis is a protozoal infection, manifested by an ulcerative process in the large intestine and damage to internal organs with the formation of abscesses. The disease is most widespread in regions with tropical and subtropical climates; in terms of mortality among parasitic infections, it ranks second in the world after malaria. Amoebiasis is recorded as sporadic cases, epidemic outbreaks are rare. Amoebiasis mainly affects middle-aged patients.
The causative agent of amoebiasis – histolytic amoeba (Entamoeba histolytica) belongs to the pathogenic protozoa and has two stages of the life cycle: the resting stage (cyst) and vegetative (trophozoite), replacing each other depending on the conditions of existence. Vegetative forms of amoeba (precystic, luminal, large vegetative and tissue) are very sensitive to changes in temperature, humidity, pH, therefore they quickly die in the external environment. Cysts show significant resistance outside the human body (they remain in the soil for up to 1 month, in water – up to 8 months).
Mature cysts, once in the lower gastrointestinal tract, transform into a non-pathogenic lumen form that lives in the lumen of the colon, feeding on detritus and bacteria. This is the stage of asymptomatic carriage of amoebas. In the future, the lumen form is either incised or transformed into a large vegetative form, which, due to the presence of proteolytic enzymes and specific proteins, is introduced into the epithelium of the intestinal wall, passing into a tissue form. Large vegetative and tissue forms are pathogenic, found in acute amoebiasis. The tissue form parasitizes in the mucous and submucosal layers of the colon wall, causing destruction of the epithelium, violation of microcirculation, formation of microabcesses with further tissue necrosis and multiple ulcerative lesions. The pathological process in the intestine spreads most often to the blind and ascending parts of the colon, less often to the sigmoid and rectum. Histolytic amoebas as a result of hematogenic dissemination are able to enter the liver, lungs, brain, kidneys, pancreas with the formation of abscesses in them.
The main source of amoeba infection is patients with a chronic form of amoebiasis in remission, as well as convalescents and carriers of cysts. Flies can be carriers of amoeba cysts. Patients with an acute form or with a relapse of chronic amoebiasis do not pose an epidemic danger, since vegetative forms of amoebas that are unstable in the external environment are isolated. Infection occurs by fecal-oral route when food and water infected with mature cysts enter the gastrointestinal tract of a healthy person, as well as by household means through contaminated hands. In addition, transmission is possible during anal intercourse, mainly among homosexuals.
Risk factors for infection are non-compliance with personal hygiene, low socio-economic status, living in areas with a hot climate. The development of the disease can be triggered by an immunodeficiency condition, dysbiosis, an unbalanced diet, stress.
Symptoms of amoebiasis
The incubation period of amoebiasis lasts from 1 week to 3 months (usually 3-6 weeks). According to the severity of symptoms, amoebiasis can be asymptomatic (up to 90% of cases) or manifest; according to the duration of the disease – acute and chronic (continuous or recurrent); according to the severity of the course – mild, moderate, severe. Depending on the clinical picture, there are 2 forms of amoebiasis: intestinal and extra-intestinal (amoebic abscesses of the liver, lungs, brain; genitourinary and cutaneous amoebiasis). The disease can manifest itself as a mixed infection with other protozoal or bacterial intestinal infections (for example, dysentery), helminthiasis.
Intestinal amoebiasis is the main, most common form of the disease. The leading symptom of the intestinal form is diarrhea. The stool is plentiful, liquid, first of a fecal nature with an admixture of mucus up to 5-6 times a day; then the bowel movements take the form of a jelly-like mass with an admixture of blood, and the frequency of defecation increases to 10-20 times a day. There are constant increasing pains in the abdomen, in the iliac region, more on the right. When the rectum is affected, painful tenesmus worries, when the appendix is affected, symptoms of appendicitis occur. There may be a moderate increase in temperature, asthenovegetative syndrome. The severity of the process with intestinal amoebiasis subsides after 4-6 weeks, after which a prolonged remission occurs (several weeks or months).
Spontaneous recovery is extremely rare. Without treatment, exacerbation develops again, and intestinal amoebiasis acquires a chronic recurrent or continuous course (lasting up to 10 years or more). Chronic intestinal amoebiasis is accompanied by disorders of all types of metabolism: hypovitaminosis, exhaustion, up to cachexia, edema, hypochromic anemia, endocrinopathies. Weakened patients, young children and pregnant women may develop a lightning-fast form of intestinal amoebiasis with extensive ulceration of the colon, toxic syndrome and death.
Of the extra-intestinal manifestations, amoebic liver abscess is the most frequent. It is characterized by single or multiple ulcers without a pyogenic membrane, localized most often in the right lobe of the liver. The disease begins acutely – with chills, hectic fever, profuse sweating, pain in the right hypochondrium, which increases with coughing, changing the position of the body. The condition of patients is severe, the liver is sharply enlarged and painful, the skin is earthy, sometimes jaundice develops. Amoebiasis of the lungs occurs in the form of pleuropneumonia or lung abscess with fever, chest pain, cough, hemoptysis. With amoebic abscess of the brain (amoebic meningoencephalitis), focal and cerebral neurological symptoms, pronounced intoxication are observed. Cutaneous amoebiasis occurs a second time in weakened patients, manifested by the formation of slightly painful erosions and ulcers with an unpleasant odor in the perianal region, on the buttocks, in the perineum area, on the abdomen, around fistula openings and postoperative wounds.
Intestinal amoebiasis can occur with various complications: perforation of an intestinal ulcer, bleeding, necrotic colitis, amoebic appendicitis, purulent peritonitis, intestinal stricture. With extra-intestinal localization, an abscess breakthrough into the surrounding tissues with the development of purulent peritonitis, pleural empyema, pericarditis or the formation of fistulas is not excluded. In the chronic course of the disease, a specific tumor-like formation from granulation tissue is formed in the intestinal wall around the ulcer – an amoeboma, leading to obstructive intestinal obstruction.
When diagnosing intestinal amoebiasis, clinical signs, epidemiological data, results of serological studies (RIF, ELISA), rectoromanoscopy and colonoscopy are taken into account. Endoscopically, with amoebiasis, characteristic ulcers of the intestinal mucosa at different stages of development are detected, with chronic forms – cicatricial strictures of the colon. Laboratory confirmation of intestinal amoebiasis is the identification of tissue and large vegetative forms of amoeba in the patient’s feces and the separated bottom of ulcers. The presence of cysts, luminal and precyst forms of the pathogen indicates amoebic carrier. Serological reactions show the presence of specific antibodies in the blood serum of patients with amoebiasis.
Extra-intestinal amoebic abscesses help to visualize a comprehensive instrumental examination, including ultrasound of the abdominal cavity, radioisotope scanning, chest X-ray, CT of the brain, laparoscopy. The detection of pathogenic forms of the pathogen in the contents of abscesses is proof of its amoebic origin. Differential diagnosis of amoebiasis is carried out with dysentery, campylobacteriosis, balantidiasis, schistosomiasis, Crohn’s disease, ulcerative colitis, pseudomembranous colitis, colon neoplasms; in women – with endometriosis of the colon. Amoebic abscesses of extra-intestinal localization differentiate from abscesses of other etiology (echinococcosis, leishmaniasis, tuberculosis).
Treatment of amoebiasis
Amoebiasis is treated on an outpatient basis, hospitalization is necessary for severe course and extra-intestinal manifestations. For the treatment of asymptomatic carriage and prevention of relapses, direct-acting luminal amoebocides (ethofamide, diloxanide furoate, iodine preparations, monomycin) are used. Systemic tissue amoebocides (metronidazole, tinidazole, ornidazole) are effective in the treatment of intestinal amoebiasis and abscesses of various localization. For the relief of colitic syndrome, acceleration of reparative processes and elimination of pathogenic forms of amoebas, iodochloroxyquinoline is prescribed. With intolerance to metronidazole, the use of antibiotics (doxycycline, erythromycin) is indicated. The combination of drugs, their doses and the duration of therapy is determined by the form and severity of the disease.
In the absence of the effect of conservative tactics and the threat of an abscess breakthrough, surgical intervention may be required. With small amoebic abscesses, it is possible to perform a puncture under the control of ultrasound with aspiration of the contents or an autopsy with drainage of the abscess and subsequent administration of antibacterial and amoebocidal drugs into its cavity. With pronounced necrotic changes around an amoebic ulcer or intestinal obstruction, intestinal resection is performed with the imposition of a colostomy.
Prognosis and prevention
With timely specific treatment, in most cases the prognosis of intestinal amoebiasis is favorable. In case of late diagnosis of amoebic abscesses of other organs, there is a risk of death. Prevention includes early detection and full-fledged treatment of patients and amoebic carriers, compliance with the sanitary and hygienic regime in everyday life, provision of high-quality water supply and wastewater treatment, food safety control, sanitary education.