Bubonic and/or pneumonic plague, which is caused by the bacterium Yersinia
pestis, which lives in the fleas of rodents.
The flees bite people and transmit the disease. This is the "black death" of the middle ages. The treatment for the disease is various antibiotics including streptomycin, ciprofloxicin, Doxycycline
and others. It often occurs in outbreaks and can be fatal if not treated.
Answer assisted by David Miller, Medical Student