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What causes dysentery (shigellosis)?
Last reviewed: 06.07.2025
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Causes of shigellosis (dysentery)
Shigella are morphologically indistinguishable from each other - they are gram-negative, non-motile rods, do not have capsules or flagella, do not form spores, easily reproduce on ordinary nutrient media, and are facultative anaerobes.
- Shigella subgroup A (Shigella dysenteriae) differ from other types of Shigella by their ability to produce exotoxin. The thermolabile fraction of the exotoxin has a pronounced neurotropic effect, especially on the autonomic nervous system.
- Shigella subgroup B (Shigella flexneri) are equipped with fimbriae (pili), i.e. superficial cilia, with the help of which they adhere to the epithelial cells of the intestine - colonocytes.
- Shigella subgroup D (Shigella Sonnei), unlike other species, are serologically homogeneous, but are divided into 7 enzymatic types, and in relation to typical phages - into 64 phage types 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 gastrointestinal tract through the mouth. The introduction of a live culture of Shigella directly into the rectum does not cause the disease.
In the stomach and throughout the entire gastrointestinal tract, under the influence of enzymes and other factors, endotoxin is released, which, when absorbed into the blood, leads to the development of general toxic syndrome, and in the case of massive invasion - to endotoxemia and neurotoxicosis and even to endotoxin shock.
Shigella toxins increase the permeability of the vascular wall, increase its fragility and thus lead to the development of local hemorrhagic syndrome, and in severe cases, DIC syndrome.
The reproduction of Shigella begins already in the small intestine, but this process occurs most intensively in the large intestine, mainly in its distal sections (sigmoid, rectum), previously sensitized by endo- or exotoxins of Shigella through the circulatory system.