While people often consider plague (aka the ‘black death’) to be something from history books, it is in fact still alive and well is some areas of the world. In North America, it is most common in the southwestern US but can extend into other regions.

Plague is caused by the bacterium Yersinia pestis, which is carried primarily by wild rodents. Infection with Yersina pestis can cause bubonic plague (swollen lymph glands), septicemia plague (bloodstream infection) or pneumonic plague (pneumonia/lung infection). An average of 13 human cases are diagnosed in the US every year. In today’s modern times, the infection can be effectively treated with antibiotics, but if left untreated the mortality rate is still 50-90%. The Canadian Notifiable Disease Database has never received a report of plague in a human.

Plague has been reported in a variety of animal species, including cats and dogs. However, dogs seem to be relatively resistant to the infection compared to cats. Yersinia pestis gets from rodents to other animals and people mainly by flea bites. Fleas become infected by biting an infected animal, and can then pass on the infection by biting another animal or person. It is also possible for plague to be transmitted by direct contact with infected animals, but this is less common.

A recent report described an outbreak of plague in prairie dogs in western South Dakota. There is concern that the disease could also affect the endangered black-footed ferret in that area. Plague almost always kills prairie dogs, and black-footed ferrets almost exclusively eat prairie dogs.

When plague is present in wild animals in a region, there is always a risk of transmission to people and pets through contact with infected animals or bites from infected fleas. Some basic measures to reduce the risk of plague exposure in areas where the disease exists in wild animals are:

Keep cats indoors

Talk to your veterinarian about a flea control program for your pets

Never touch wild animals, especially sick or dead ones

Don’t keep wild animals as pets

Try to keep wild animals away from your pets

Photo: Scanning electron micrograph of an Oriental Rat Flea, Xenopsylla cheopis.

(Centers for Disease Control and Prevention (CDC) / Janice Carr)