Animal Health – Plague

Factsheet - ISSN 1198-712X   -   Copyright King's Printer for Ontario
Agdex#: 400/660
Publication Date: January 2013
Order#: 13-013
Last Reviewed:
Written by: Tim Pasma

Table of Contents

  1. Cause
  2. Clinicial Signs
  3. Treatment
  4. Protection and Management
  5. Transmission to Humans
  6. Reporting

Plague is a disease of rodents, cats and dogs that can also spread to humans. Rodent and flea control will help prevent the spread of plague.


Plague is caused by the bacterium Yersinia pestis. The bacteria are found in rodents (Figure 1), and fleas can carry the bacteria from an infected rodent to other animals, including dogs and cats.

Clinical Signs

There are three forms of plague: bubonic, septicemic and pneumonic. Animals with bubonic plague develop fever, poor appetite and appear depressed. Enlarged lymph nodes and abscesses called buboes appear on the body, and these abscesses may rupture and drain pus.

Animals with septicemic plague develop fever and lethargy and may have other signs such as diarrhea, vomiting and circulatory problems.

Two mice hunched in a corner

Figure 1. The bacterium is commonly found on rodents.

Animals with pneumonic plague have all the signs of septicemic plague, plus cough and pneumonia.

Livestock are not known to be affected by plague. Cats are more likely to be affected than dogs (Figure 2).


Have a veterinarian see an animal that is suspected of being infected with plague immediately, as the disease progresses quickly. A veterinarian can confirm whether an animal is infected with plague and prescribe treatment. An infected animal is likely to require isolation in a veterinary clinic with close monitoring.

Prevention and Management

To keep pets from being infected with plague, keep them from roaming and hunting, limit their contact with rodent carcasses and use flea control. Rodent control is also important.

Orange kitten outside sitting on the grass

Figure 2. Cats are more likely to be affected.

Transmission to Humans

People exposed to infected animals or fleas are at risk of contracting plague.

Bubonic plague will result from a bite from an infected flea that has fed on an infected rodent, such as a rat. Pneumonic plague can be spread through airborne droplets released by the coughs or sneezing of an infected person or animal, especially cats.

Plague is highly contagious. Owners should never attempt to diagnose or treat the disease on their own – a number of human cases have occurred in people who handled sick cats. Hunters are also at risk if they skin an infected animal. Outbreaks have also occurred in areas of poor housing with inadequate sanitation.


Veterinary laboratories in Ontario and veterinarians who use a laboratory outside of Ontario must notify the Ontario Ministry of Agriculture and Food and Ministry of Rural Affairs (OMAF and MRA) when a case of plague is diagnosed in an animal. OMAF and MRA will take measures to prevent the spread of the disease and will notify public health officials, who will follow up on people potentially exposed to the disease.

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