Cute Rat

Wild rodents, including rats, can carry many different zoonotic pathogens, such as Leptospira, Toxoplasma gondii, and Campylobacter. The Black Death is traditionally believed to have been caused by the micro-organism Yersinia pestis, carried by the Tropical Rat Flea (Xenopsylla cheopis) which preyed on Black Rats living in European cities during the epidemic outbreaks of the Middle Ages; these rats were used as transport hosts. Other zoonotic diseases linked to pest rodents include Classical swine fever and Foot-and-mouth disease.
The average lifespan of any given rat depends on which species is being discussed, but many only live about a year due to predation.