Several diseases affect black-footed ferrets, the most serious being canine distemper and sylvatic plague. Canine distemper is thought always to be fatal to ferrets. It is spread by other animals that frequent prairie dog towns, including coyotes, badgers and skunks. It was the main cause of the catastrophic losses of ferrets in northwestern Wyoming in 1985 and 1986. Sylvatic plague is the wildlife version of bubonic plague that devastated the human population in Europe in the Middle Ages.
Prairie dogs are susceptible to plague, and entire dog towns can be eliminated quickly.
Although ferrets were thought to be resistant to the disease, the death of a captive ferret in 1994 to plague it acquired from eating an infected prairie dog is cause for concern. Ferrets are also susceptible to other diseases, including rabies, tularemia and human influenza, but those diseases are not known to pose a serious threat. None is considered a serious concern. Inbreeding is another problem that can arise with the breeding of closely related animals carrying the same recessive problem gene. Even if a recessive trait does not show in the breeding animals, it will be seen in the offspring.