What is Shigellosis?
Shigellosis is an acute anthroponous infectious disease with fecal-oral transmission mechanism. General intoxication and predominant lesion of the mucous membrane of the distal colon, cramping abdominal pains, frequent loose stools with an admixture of mucus and blood, and tenesmus are characteristic.
Clinical descriptions of the disease are given for the first time in the writings of the Syrian physician Areteus of Cappadocia (I century BC) under the name “bloody, or strained, diarrhea” and in ancient Russian manuscripts (“bloody womb”, “washed”).
In the medical literature of the XVII – XIX century, the tendency of the disease to widespread in the form of epidemics and pandemics was emphasized. The properties of the main causative agents of dysentery are described at the end of the 19th century (Raevsky A.S., 1875; Chantemess D., Vidal F., 1888; Kubasov P.I., 1889; Grigoryev A.V., 1891; Shiga K., 1898), Later, several other types of pathogens were discovered and described.
Causes of Shigellosis
The causative agents are gram-negative immobilized bacteria of the genus Shigella of the Enterobacteriaceae family. According to the modern classification, Shigella are divided into 4 groups (A, B, C, D) and, accordingly, into 4 species – S. dysenteriae, S. flexneri, S. boydii, S. sonnei. Each of the species, except for Shigella Sonne, includes several serovars. Among S. dysenteriae, 12 independent serovars are distinguished (1 – 12), including Grigoriev-Shigi (S. dysenteriae 1), Stutzer-Schmitz (S. dysenteriae 2) and Large-Sachs (S. dysenteriae 3-7). S.flexneri includes 8 serovars (1-6, X and Y), including Newcastle (S.flexneri 6). S. boydii include 18 serovars (1 – 18). S. sonnei do not serologically differentiate. In total, there are about 50 Shigella serovars. The etiological role of different shigella is not the same. Of the greatest importance in almost all countries are Shigella Sonne and Shigella Flexner – pathogens of the so-called large nosological forms. The etiological significance of the individual Shigella serovars is not the same. Among S. flexneri, subserovars 2a, lb and serovar 6 dominate, among S. boydii – serovars 4 and 2, among S. dysenteriae – serovars 2 and 3. Biochemical variants of He, Ilg and 1a prevail among S. sonnei.
The causative agents of bacterial dysentery are distinguished by enzymatic activity, pathogenicity and virulence. All shigella grow well on differential diagnostic environments; temperature optimum of 37 ° C, Sonne bacteria can multiply at 10-15 ° C.
Shigella are not very stable outside the human body. Virulence of bacteria is quite variable. The virulence of Shigella Flexner, especially subserovar 2a, is quite high. Shigella Sonne is the least virulent. They are distinguished by a large enzymatic activity, unpretentiousness to the composition of nutrient media. They multiply intensively in milk and dairy products. At the same time, their storage time exceeds the product sales time. The pronounced deficiency of virulence in Shigella Sonne is fully compensated by their high biochemical activity and the rate of reproduction in the infected substrate. It takes 8 to 24 hours to accumulate a dose of S. sonnei that infects adults in milk at room temperature. In the hot season, these periods are minimal: it takes only 1-3 hours to accumulate a sufficient dose of bacteria to infect children. the Shigella Sonne breeding in contaminated products accumulates thermostable endotoxin, which can cause severe injuries in case of negative results of bacteriological studies of infected foods. S. sonnei also has a high antagonistic activity against saprophytic and lactic acid microflora.
An important feature of Shigella Sonne is their resistance to antibacterial drugs. Outside the body, the resistance of Shigella of different species is not the same. Shigella Sonne and Flexner can be stored in water for a long time. When heated, shigella quickly die: at 60 ° C – for 10 minutes, when boiled – instantly. Least resistant S.flexneri. In recent years, thermoresistant (capable of surviving at 59 ° C) strains of Shigella Sonne and Flexner are often isolated. Disinfectants in normal concentrations act destructively on shigella.