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Based on epizootological and epidemiological investigations in the Vologda province since 1958 till 2000, the combined territorial and temporal manifestations of natural foci of diseases was revealed. A natural focus occupies a complex of biotopes, and in different time the focus is activated in different areas, such as a river plain, marsh, meadow-field, and forest. Most commonly an activation of the natural focus appears in a border zone of three biotopes, namely, a forest, meadow-field, and river plain. A dependence of activation of various natural foci upon local climate conditions and fluctuations of micromammalian host number are considered.