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Amoebiasis: an overview
Last reviewed: 23.04.2024
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Amebiasis (English amebiasis) is anthroponous protozoal disease with fecal-oral transmission mechanism. Amoebiasis is characterized by ulcerative lesions of the colon, a tendency to a chronic recurrent course, extraintestinal complications in the form of abscesses of the liver and other organs.
[Epidemiology of amebiasis
The source is a man (mainly a carrier of luminal forms), which releases feces from the amoebas with feces. The mechanism of transmission is fecal-oral. Transmission ways - water, alimentary, contact-household. Transmission factors include water, food products (mainly vegetables and fruits not subjected to heat treatment), household items. Cysts can spread by mechanical vectors: flies and cockroaches, in the digestive system of which the amoebae remain viable for several days.
Susceptibility is relative. Seasonality is not celebrated; some increase in the incidence in the warm season is associated with exacerbations of intestinal amebiasis caused by various causes, especially the layering of acute intestinal infections. In countries with temperate climatic zones, E. Dispar infection is 10 times higher than E. Histolytica; the latter prevails in tropical countries. Specific antibodies in E. Histolytica infestation do not play a significant protective role. Immunity with amebiasis does not protect against relapse and reinfection. Since it is unstable and unsterile.
High amoebiasis of the population is noted in Southeast Asia, South and Central America, South and West Africa. Disease of amoebiasis is common in the CIS countries, Transcaucasia and Central Asia. Approximately 480 million people - carriers of E. Histolytica, 48 million of them develop colitis and extraintestinal abscesses, more than 50 thousand patients are fatal. In Russia sporadic cases, mostly imported, are detected in all regions; The risk of amebiasis is higher in the southern regions of the country.
What causes amoebiasis?
Amoebiasis is caused by Entamoeba histolytica, which is attributed to the half-kingdom of Protozoa, the subtype of Sarcodina, the class of Rhizopoda, the order of Atoibi, the family of Entamoebidae.
The life cycle of E. Histolytica includes two stages - vegetative (trophozoite) and resting stage (cyst). The shallow vegetative form (luminal form, or forma minuta) has sizes from 7 to 25 microns. The division of the cytoplasm into ecto- and endoplasm is poorly expressed. This non-pathogenic, commensal form lives in the lumen of the human colon, feeds on bacteria through endocytosis, is mobile, propagates vegetatively. Tissue form (20-25 microns) is found in the affected tissues and organs of the host. It has an oval nucleus, a well-expressed vitreous ectoplasm and granular endoplasm, is very mobile, forms broad, blunt pseudopodia. A large vegetative form ( forma magna) is formed from a tissue form.
Pathogenesis of amoebiasis
The reason why E. Histolytica passes from a luminal state to tissue parasitism, is not fully understood. It is believed that the main virulence factor in E. Histolytica is cysteine proteinase. Which are absent in E. Dispar. In the development of invasive forms of amoebiasis, factors such as the intensity of infestation, changes in the physico-chemical environment of intestinal contents, immunodeficiency, starvation, stress, etc., are important. They note the relatively frequent development of invasive forms in women during pregnancy and lactation, in persons infected HIV. Probably, amoebae pass to tissue parasitism with the acquisition of properties characteristic of other pathogenic microorganisms, such as adhesiveness, invasiveness, the ability to act on the protective mechanisms of the host, etc. It has been established that trophozoites attach to epithelial cells due to a specific lectin-galactose-N-acetylgalactosamine. In E. Histolytica found hemolysin, proteases, some strains - hyaluronidase, which can play a significant role in the destruction of amoebae epithelial barrier.
What are the symptoms of amoebiasis?
In countries where E. Histolytica is widespread , 90% of infected individuals report non-invasive amebiasis, and they are thus asymptomatic carriers of luminal forms of amoebas, and only 10% of infected develop invasive amebiasis.
Invasive amebiasis has two main forms - intestinal and extra-intestinal.
When lesions are localized in the rectosigmoidal region of the colon, the symptoms may correspond to a dysentery-like syndrome with tenesmus and occasionally with an admixture of mucus, blood and pus in the stool. When the lesions are localized in the caecum, constipation with pain in the right ileal region and symptoms characteristic of the clinical picture of chronic appendicitis (in a number of cases appendicitis actually develops). In the ileum, amebic lesions are relatively rare.
How is amebiasis diagnosed?
The most reliable diagnosis of amebiasis of the intestinal is a microscopic examination of feces for the detection of vegetative forms (trophozoites) and cysts. Trophozoites are better to identify in patients with diarrhea, and cysts - in a decorated stool. Primary microscopy examines native preparations from fresh samples of feces with saline. To identify trophozoites, amebic preparations are stained with Lugol's solution or buffered methylene blue. To identify cysts, native preparations prepared from fresh or preservative-treated faeces are stained with iodine. Detection of amoebas is more effective in the immediate investigation of feces after the appointment of a laxative.
What do need to examine?
Who to contact?
How is amebiasis treated?
Amoebiasis is treated with drugs that can be divided into two groups - contact (luminal). Affecting the intestinal luminal forms, and systemic tissue amoebicides.
Non-invasive amebiasis (asymptomatic carriers) is treated with luminal amoebicides. They are recommended to be prescribed also after the end of the treatment with tissue amoebicides for elimination of amoebas, possibly remaining in the intestine. If it is impossible to prevent re-infection, the use of luminal amoebicides is impractical. In these situations, luminal amoebicides should be prescribed for epidemiological reasons, for example, individuals whose professional activities may contribute to the infection of other people, in particular employees of catering enterprises.
Drugs
Prevention of amebiasis
Amybiasis can be prevented if one deals with protecting water from faecal pollution and ensuring high-quality water supply; prevention of food contamination by amoeba cysts; early detection and treatment of amoebiasis, as well as asymptomatic carriers; systematic health education. Boiling water is a more effective method of destroying cyst amoebae than using chemicals.
What prognosis does amoebiasis have?
Currently, amoebiasis is considered almost completely curable disease, provided early diagnosis and adequate therapy. However, developing complications of intestinal amebiasis and liver abscesses remain the main cause of death.