Plague

May 2026

Plague is a serious disease caused by the bacteria Yersinia pestis that can affect both humans and animals.

There are three forms of plague:

  • Bubonic plague results from the bite of an infected flea that has fed on an infected rodent, such as a mouse or rat. The infection appears in the lymph nodes, causing them to swell and become painful. This swollen node is known as a ‘bubo’ (which gives the name bubonic). Bubonic plague is the most common form.
  • Pneumonic plague infects the lungs and can spread person to person through respiratory droplets when the ill person coughs or sneezes. Without treatment, pneumonic plague is often fatal. It is the least common form of plague. This form could potentially be used in a bioterrorism attack. No bioterrorist attack using the bacteria that causes plague has happened in modern times.
  • Septicemic plague occurs when the infection spreads through the bloodstream. Both bubonic and pneumonic plague can progress to septicemic plague, which is generally fatal without treatment.

Symptoms usually start one to seven days after a bite from an infected flea (bubonic plague) and one to four days after exposure for pneumonic plague.

Symptoms may include:

  • Fever
  • Chills
  • Headache
  • Muscle pain
  • Weakness
  • Swollen and painful lymph nodes, also known as “bubos”
  • Pneumonia (lung infection)
  • Shortness of breath
  • Chest pain
  • Cough
  • Bloody or watery mucus

If left untreated, this may lead to respiratory failure, shock, and death.

Bubonic plague results from the bite of an infected flea that has fed on an infected rodent, such as a rat, mouse, or prairie dog or, less commonly, by handling tissues of an infected animal.

Pneumonic plague can spread person to person through respiratory droplets when an infected person coughs or sneezes. People can become infected if they breathe the contaminated air or touch contaminated surfaces, then touch their eyes, nose or mouth.

Plague once caused major outbreaks around the world, including the Black Death in 14th century Europe. Today, cases are rare because of better living conditions, public health measures and antibiotics.

Plague is found in rodents (and their fleas) in Africa, Asia, South America, and south-west USA. Plague is not known to be present in Canada. The three countries with the highest number of reported cases of plague in humans are the Democratic Republic of Congo, Madagascar, and Peru. A small number of human plague cases are reported each year in the western United States of America. These cases are usually from contact with wild animals or outdoor cats.

If you think you have plague, before you visit a doctor or a hospital, call Toronto Public Health immediately.

Toronto residents should call 416-338-7600, Monday to Friday, from 8:30 a.m. to 4:30 p.m., or call 311 after hours and ask to speak to the Communicable Disease Manager. Let health care workers know of your potential exposure to plague before seeking health care.

Toronto Public Health will make appropriate arrangements for your medical assessment. Describe your symptoms over the phone, where you have been travelling and mention any possible exposure to plague.

If you think you are infected with plague, it is important that you isolate immediately:

  • Stay home, separate yourself from those around you and do not have physical contact with people, pets or animals.
  • Do not take public transportation, taxi or ride share.
  • Wash or sanitize your hands often and cover your cough or sneeze with your elbow or a tissue.
  • Wear a well-fitting, high-quality mask.
  • Avoid contact between others and your body fluids, including mucus or pus, and items contaminated by them, such as clothing or bedding.

      Plague is diagnosed through laboratory testing including a blood test or testing of body fluids.

      Plague can be treated effectively with antibiotics, but they must be given quickly.  Many people also need hospital care. Close contacts of people with pneumonic plague may be given a preventive antibiotic.

      If you are visiting areas where plague is known to occur, you can reduce the likelihood of being bitten by infected fleas:

      • Apply insect repellent approved by Health Canada, following manufacturer’s instructions.
      • Avoid direct contact with rodents or other wildlife, sick or dead animals, and people who are sick or are suspected to be infected with pneumonic plague.
      • Make homes, recreation places and workplaces less attractive to rodents, such as rats, by removing food sources, storing garbage safely, and eliminating nesting materials.
      • Do not allow pets to sleep on your bed, especially “outdoor” cats and dogs.

      Currently, there is no vaccine available for plague. Research is ongoing to develop an effective vaccine.

      Call Toronto Public Health at 416-338-7600 (TTY at 416-392-0658) or speak to your health care provider. You can also call 811 to connect to a registered nurse day or night for free, secure and confidential health advice.
      Date modified: May 29, 2026