[Role of fleas, the principal and secondary plague vectors, in the circulation of the causative agent in Siberian natural foci].

The paper reviews data on the role of fleas as the principal and secondary vectors of infection in the Siberian natural foci of plague. The role of Citellophilus tesquorum as the principal plague vectors in the Transbaikalian and Tuvinian natural foci is shown to be determined by their ecological characteristics (the degree of specificity to the main host, numbers, and natural infection) to a greater extent and by the rate of block formation to a lesser extent. The significance of principal and secondary vectors is estimated in the circulation of the causative agent in the monovectoral (Transbaikalian and Tuvinian) and multivectoral (Gorno-Altai) foci of plagues. It is suggested that the "microfocal" form (phenotype) of the agent's existence is characteristic of the Siberian natural foci where the rate of block formation does not generally show high indices. This phenomenon might be a basis for the long circulation of the plague microbe in the mountain (Tuva and Gorno-Altai) foci where protracted interepizootic periods have not been registered.