[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.