Here's an epidemiological detective story. In many diseases, the only reservoir is other humans. In communities where this happens from time to time, plague is endemic . When fleas pass Y. pestis on to domestic rats, the fleas on these rats can then pass Y. pestis on to large numbers of humans. Subcutaneous hemorrhaging makes dark areas.
Pneumonic plague can spread from person to person independently of animal reservoirs or vectors.
Here's a link to a discussion of the recent increase in plague cases in the South Western U.S.A. . Almost all Rickettsia spp. are obligate intracellular parasites. These have been effectively controlled with vaccines. Vaccines can be very effective. Before antibiotics, isolation was all one could do.