What causes shigellosis (bacterial dysentery)?

Cause of dysentery

Dysentery is caused by a number of biologically related microorganisms belonging to the Enterobacteriacea family and united in the genus Shigella. According to modern classification, the genus Shigella is divided into four species:

1. group A: Shigella Dysenteriae, 1 - Grigorieva-Shiga, Shigella Dysenteriae, 2 - Stutzer-Schmitz and Shigella Dysenteriae 3-7 - Large-Sachs;
2. group B: Shigella Flexneri with subspecies Shigella Flexneri 6 - Newcastle; serovars 1-6, each of which is subdivided into subserovars a and b, as well as serovars 6, X and Y;
3. group C: Shigella Boydi, serovars 1-18;
4. Group D: Shigella Sonnei.

Shigella are gram-negative non-motile rods, facultative aerobes. The Grigoriev-Shiga rod produces shigitoxin (exotoxin), other species contain heat-labile endotoxin - LPS. The lowest infectious dose is characteristic of Grigoriev-Shiga bacteria, the highest - for bacteria

Flexner and the greatest - for Sonne bacteria. Representatives of the last two species are the most stable in the environment: on dishes and damp linen they can survive for months, in soil - up to 3 months, on food products - several days, in water - up to 3 months. When heated to 60 °C they die in 10 minutes, when boiled - immediately, in disinfectant solutions - within a few minutes. Of the antibacterial drugs, the greatest sensitivity in vitro is noted for fluoroquinolones (100%).

Pathogenesis of dysentery

Shigella can remain in the stomach for 24 hours (sometimes longer). Some of them disintegrate there, releasing endotoxin. The remaining bacteria enter the small intestine, where they can linger for up to several days and even multiply. Shigella then move to the lower sections of the intestine, where they also multiply and disintegrate in greater quantities than in the small intestine. The determining factor in the development of the infectious process in shigellosis is the ability of shigella to intracellular invasion. Of primary importance among the protective mechanisms is the state of natural resistance factors, especially local ones (lysozyme and beta-lysins of the mucous membrane of the distal colon). Together with humoral factors (bactericidal activity, lysozyme, serum complement), they respond to the development of the infectious process throughout the disease.

The degree of non-specific resistance is to a certain extent determined genetically, but at the same time it depends on a number of factors: the patient’s age, nutritional status, and concomitant diseases.

Epidemiology of dysentery

The only source of the shigellosis pathogen is a person with a manifest or latent form of the disease, as well as a bacteria excretor. The greatest danger is posed by patients who, by the nature of their work, are associated with cooking, storing, transporting and selling food products. Dysentery is spread by the fecal-oral mechanism of pathogen transmission. This mechanism includes transmission of the pathogen by contact-household, water, and food. The disease is widespread, but the incidence is predominant in developing countries among the population with an unsatisfactory socio-economic and sanitary-hygienic status. Summer-autumn seasonality is typical for countries with a temperate climate.

The susceptibility of the population to shigellosis is high in all age groups, children are most often affected. After the disease, a short-term type-specific immunity is formed.

Specific prevention of dysentery has not been developed. Non-specific prevention measures include improving the sanitary culture of the population, disinfecting drinking water (chlorination, boiling, etc.), and following the rules for the preparation, storage, and sale of food products. Food industry workers and persons equivalent to them are allowed to work only after a negative bacteriological test for shigellosis, and after suffering shigellosis - after two negative test results taken no earlier than the 3rd day after treatment, and the absence of clinical manifestations. If the patient is staying at home, routine disinfection is carried out in the apartment. Persons who have been in contact with patients are placed under medical observation for 7 days.

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