Plague is a flea-transmitted disease that naturally infects the majority of rodent genera, and is caused by the bacterium Yersinia pestis. Certain resistant rodent species, such as field mice, serve as reservoirs for the disease, while other mammals, most notably prairie dogs, black-footed ferrets, cats, and primates, are highly susceptible to the disease. Plague is a worldwide threat to human health and has been responsible for three human pandemics.
Species highly susceptible to plague usually die so quickly after infection that field signs may be subtle. External swelling, or buboes, may or may not be present depending on mode of exposure to the bacteria.