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What causes dysentery (shigellosis)?
Last reviewed: 20.11.2021
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The causes of shigellosis (dysentery)
Shigella are morphologically indistinguishable from each other - they are Gram-negative fixed sticks, capsules and flagella do not, spores do not form, multiply easily on ordinary nutrient media, facultative anaerobes.
- Shigella subgroup A (shigella dysentery) differ from other Shigella species ability to produce exotoxin. Thermolabile fraction exotoxin has a pronounced neurotropic effect, especially on the autonomic nervous system.
- Shigella of subgroup B (Shigella Flexner) is equipped with pili (pili), i.e. Surface cilia, with the help of which they adhere to epithelial cells of the intestine - the colonocytes.
- Shigella of subgroup D (Shionella Sonne), unlike other species, are serologically homogeneous, but are divided into 7 enzymatic types, and in relation to type phages - by 64 phagotypes and can give spontaneous agglutination with all (or most) dysentery agglutinating sera.
Pathogenesis of shigellosis (dysentery)
The disease develops only when the pathogen enters the digestive tract through the mouth. The introduction of live shigella culture directly into the rectum does not cause disease.
In the stomach and throughout the gastrointestinal tract, endotoxin is released under the action of enzymes and other factors, which, absorbed into the blood, leads to the development of a general toxic syndrome, and in case of massive invasion - to endotoxinemia and neurotoxicosis and even endotoxin shock.
Shigella toxins increase permeability of the vascular wall, increase its fragility and thus lead to the development of local hemorrhagic syndrome, and in severe cases - DIC syndrome.
Reproduction of shigella begins already in the small intestine, but this process occurs most intensively in the large intestine, mainly in its distal parts (sigmoid, rectum), previously sensitized by endo- or exotoxins of shigella through the circulatory system.