Who or what does the Yersinia pestis usually infect?

Answer 1

Since the beginning of the 1990s, the number of human cases of plague has been rising, and outbreaks are reappearing in various countries after decades of quiescence. Plague is therefore categorized as a reemerging disease. Until recently, Yersinia pestis was considered as uniformly susceptible to agents that are active against gram-negative bacteria. The isolation in Madagascar of two multidrug-resistant strains of Y. pestis, one resistant to all of the antimicrobial agents recommended for treatment and prophylaxis of plague and the other resistant to a smaller array of drugs, is worrisome. The demonstration that horizontal gene transfer in the flea midgut may be the source of antibiotic-resistant Y. pestis strains is of great concern and indicates that such a clinically ominous event may occur again. There is also concern that a biological attack with Y. pestis might employ a natural or engineered antimicrobial-resistant strain. Surveillance of antibiotic resistance in Y. pestis should therefore become systematic worldwide.

Answer 2

Fleas, who then carry it to the victims they bite.