What causes shigellosis (bacterial dysentery)?
Last reviewed: 23.04.2024
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The cause of dysentery
Dysentery is caused by a number of biologically close microorganisms belonging to the family Enterobacteriacea and united in the genus Shigella. According to modern classification, the genus Shigella is divided into four types:
- group A: Shigella Dysenteriae, 1 - Grigorieva-Shigi, Shigella Dysenteriae, 2 - Stutzer-Schmitz and Shigella Dysenteriae 3-7 - Larja-Saksa;
- group B: Shigella Flexneri with subspecies Shigella Flexneri 6 - Newcastle; serovars 1-6, each of which is subdivided into the sub-serovars a and b, as well as serovars 6, X and Y;
- group C: Shigella Boydi, serovars 1-18;
- group D: Shigella Sonnei.
Shigella - Gram-negative fixed sticks, facultative aerobes. The Grigoriev-Shigi rod forms shigitoxin (exotoxin), the remaining species contain thermolabile endotoxin-LPS. The smallest infecting dose is characteristic of the bacteria Grigoriev-Shigi, the big one for bacteria
Flexner and the largest - for bacteria Sonne. Representatives of the latter two species are most stable in the environment: on dishes and wet linens they can persist for months, in the soil - up to 3 months, on food - several days, in water - up to 3 months. When heated to 60 ° C, they die after 10 minutes, while boiling - immediately, in disinfectant solutions - for several minutes. Of the antibacterial drugs, the greatest sensitivity in vitro was noted for fluoroquinolones (100%).
Pathogenesis of dysentery
Within a day (sometimes longer) shigella can be in the stomach. At the same time, some of them disintegrate here, releasing endotoxin. The remaining bacteria enter the small intestine, where they can linger for several days and even multiply. Further shigella move to the lower intestine, where they also multiply and decay in larger quantities than in the small intestine. The defining moment in the development of the infectious process in shigellosis is the ability of shigella to intracellular invasion. The state of natural factors of resistance, especially local (lysozyme and beta-lysines of the mucosa of the distal colon) is of primary importance among protective mechanisms. Together with humoral factors (bactericidal activity, lysozyme, complement of blood serum), they react to the development of the infectious process throughout the disease.
The degree of nonspecific resistance is to a certain extent determined genetically, but at the same time it depends on a number of factors: the age of the patient, the nutritional value, the concomitant diseases.
Epidemiology of dysentery
The only source of the causative agent of shigellosis is a person who has a manifest or erased form of the disease, as well as a bacteriovirus. The greatest danger is represented by patients who, in the nature of their work, are associated with cooking, storing, transporting and selling food products. Dysentery is spread by the fecal-oral mechanism of transmission of the pathogen. This mechanism includes the transmission of the pathogen by contact-household, water, food. The disease is ubiquitous, but the incidence prevails in developing countries among the population with poor socioeconomic and sanitary status. For countries with a temperate climate, summer-autumn seasonality is characteristic.
The susceptibility of the population to shigellosis is high in all age groups, most often the children are sick. After the transferred disease, a short type-specific immunity is formed.
Specific prophylaxis of dysentery is not developed. Measures of nonspecific prevention consist in raising the sanitary culture of the population, disinfection of drinking water (chlorination, boiling, etc.). And also in observance of rules of preparation, storage and realization of foodstuff. Employees of food enterprises and persons equal to them are allowed to work only after negative bacteriological analysis for shigellosis, and after the transferred disease shigellosis - after two negative results of tests taken no earlier than on the 3rd day after treatment, and the absence of clinical manifestations. If the patient is staying at home, the apartment is disinfected. For persons in contact with patients, medical supervision is established for 7 days.
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