Bubonic plague still exists, especially in developing countries. British researchers studying the plague have found that its spread to humans is dependent on the resistance of the rat population. When surviving rats are resistant to the plague, it is less likely to spread to humans. However, when fleas transmit the disease to healthy, unresistant rats, the human population is at risk. Fountain H .
Plague can wax when rats wane.
Metapopulation dynamics of bubonic plague. The journal Nature on the web.