To maintain continuous circulation of plague pathogen in natural foci, the pathogen should be capable of invading host organism, resisting the bactericide protective systems of rodent, and reproducing itself to maintain the content of bacteria at a level sufficient for further transmission by fleas to a new host. Each of these stages of the Yersinia pestis circulation is determined by a variety of factors of plague pathogen, which may act either individually or in combination. Each of the factors itself may be involved in the pathological process at different stages of its development or in pathogen transmission. However, it is only the aggregate of the factors (regardless of significant or insignificant individual contribution to the sum effect) that provides persistence of plague pathogen in natural foci. The plague pathogen factors providing its transmission from one host organism to the next as well as correlation of individual factors of pathogensis and expression of various household genes with plague pathogensis virulence are considered in the second communication. This review was compiled on the basis of not only well-known works but also some sources of limited availability, particularly, for English-speaking audience.