[The range of pathogen variation due to discussion of different hypotheses of plaque].

The paper reviews the hypotheses that explain the mechanism of plague enzooty in natural foci, which are based on a concept of a wide range of plague microbial variability. A comparative analysis of the parameters of variability in the experimentally obtained plague microbial strains and "atypical" natural isolates of the causative agent has led to the conclusion that the mechanism of adaptive variability is due to a phenotypic change in ontogenesis that reflects the philogenetic pathway of the adaptability of a plague microbe to constantly changing living conditions in the ecological niche assimilated by the causative agent.

[Functional phenotypic variability in a plague pathogen and plague enzootics].

In the bacterial population, phenotypic variability plays a part of structural and functional subsystem that occupies a special place in the relations of heterogenic populations by performing an important adaptive function in the common system of ecological connections of parasitocenosis. At the same time regularly varying microorganism phenotypes act as an independent system that are closely related with the conditions of the niches occupied by the causative agent. Each subsystem as part of parasitocenosis is provided by its intrinsic adaptive mechanisms, which in combination ensures the stability of biocenosis based on self-regulation of evolutionarily established ecosystems.

[Establishment of the plague control system in Russia].

The specialized plague control facilities which began being founded as a system of institutions in Russia in 1897 have made a great contribution to epidemiological well-being against quarantine and particularly menacing diseases. The developmental stages of plague control service in different periods of the country's social life and its place in the general governmental preventive and antiepidemic measures are shown. The paper emphasizes that it is expedient to maintain the antiepidemic readiness of plaque control facilities due the fact that the epidemic situation is due menacing and zoonosis is expected to aggravate in the late 20th to the early 21st centuries.

[Genetic research on plague pathogen in plague control].

The results of molecular-genetic studies performed by Russian specialists in plague research are discussed. On their basis, new concepts concerning the factors determining virulence of the plague bacterium were formulated, and certain aspects of Yersinia taxonomy were clarified.

[Ways to improve the epidemiological surveillance for plague].

The paper deals with the plague epidemiological surveillance in natural foci and with the ways of its improvement. The diversity of methods currently used for surveillance ensures a satisfactory epidemic situation though the problem of plague control among rodents and hares in the natural foci remained unsettled. Therefore the main task of research and practical plague institutions in improving plague epidemiological surveillance in the natural foci is to provide further research evidence for the application of facilities and guidelines to control the carriers and vectors of plague, which can prevent the development of epizootics and reduce a risk for human infection in the enzootic areas.

[Cholera in Makhachkala during the 1994 epidemic].

During the period of epidemic in the Daghestan 51 patients and 27 Vibrio carriers were detected in Makhachkala. A considerable proportion (30.7%) of cholera cases caused by infection imported from regions, unfavorable with respect to cholera, in the presence of pronounced migration of the population was registered.

[The results of the measured oral infection of white mice with strains of the causative agent of plague differing in their plasmid profile].

The oral infection of mice with Y. pestis culture with different plasmid profiles by the method of feeding them with agar granules containing a definite number of these bacteria revealed that the virulence of subcultures which had lost Pst-plasmid and the capacity for fibrinolysin and plasma-coagulase production, encoded by this plasmid, decreased 10-1000 times, the loss of Fra-plasmid produced a less pronounced effect. In contrast to subcutaneous infection, in alimentary infection Y.