But the disease, which wiped out one third of the European population in earlier times, kills people in many areas of the world even today. In an entirely theoretical paper published in Nature today, M. J. Keeling and C. A. Gilligan of the University of Cambridge in England point out the importance rats play in keeping the disease going and offer advice about how to contain it.
Bubonic plague is primarily a disease of rodents, spread by fleas.
The fleas feed on an infected rat and soon become infectious. When the rat dies, they typically find a new host and thus distribute the disease in a rat population. Only when the number of rats becomes very low are the fleas forced to seek a different host. This is how they jump to human hosts, leading to an epidemic. Despite this life cycle, most plague models up to now have concentrated only on human populations.