The last reported human case of plague in Canada occurred in 1939, and in animals in 1989. Bubonic plague, the most common form of disease, results in "buboes" or swelling at the lymph glands. Fortunately, antibiotics are effective at treating plague.
Plague is a bacterial zoonotic disease (a disease we get from animals), caused by a bacterium called Yersinia pestis. It can result in three forms of disease: bubonic plague (80-95% of cases), septicemic plague (10-20% of cases), and pneumonic plague (rare). Bubonic plague affects the lymph nodes and is the most common form. Inhaling the bacteria can cause pneumonic plague, which affects the lungs, and blood poisoning can result from both forms.
Over the course of human history, three plague pandemics have been recorded: in the 6th century, the 14th century, and at the end of the 19th century. The 14th century pandemic, known as the “Black Death” killed up to a third of the European population (estimated 17-28 million people).
Fortunately, human epidemics from plague are rare today. Epidemics have occurred in Africa, Asia and South America. Since the 1990s, most cases reported have been from Africa. In recent decades, 0-17 cases have been reported each year in the United States, mostly in the West.
The primary source of the Yersinia pestis bacteria is usually infected small mammals such as rodents, shrews, and pikas. Other animal species such as cats, dogs, foxes, rabbits, mink, marten, etc., can also be infected with the bacteria. The virus spreads by:
- Infected rodent flea bites (most common route of transmission)
- Contact with an infected animal (including bites and scratches)
- Handling infected tissue
- Inhalation of respiratory droplets from infected animals or people
Bubonic plague affects the lymph nodes and is the most common form. Inhaling the bacteria can cause pneumonic plague, which affects the lungs, and blood poisoning can result from both forms. Plague can also be caused by contact with the body fluids and respiratory secretions of infected individuals. In some instances, direct contact with household cats and rabbits that have been infected can cause disease.
Symptoms of plague include:
- Fever
- Chills
- Muscle pain
- Weakness
- Headache
- Intense pain and swelling near lymph nodes (bubo)
- Cough
- Chest pain
- Shortness of breath
- Nausea
- Vomiting
- Diarrhea
- Abdominal pain
Incubation period is generally one to seven days; plague pneumonia may take less than one day, and up to four days, to incubate.
Diagnosis of Yersinia pestis can be made by identifying the organism by doing a culture or by Polymerase Chain Reaction (PCR) test of infected tissues and fluids. Viewing through a microscope may be helpful, but Y. pestis resembles other organisms so additional testing is needed to confirm its identity. Testing during the initial illness and after recovery, 2 - 4 weeks apart, can help confirm the diagnosis.
Since this organism can infect laboratory workers, it is important to let the laboratory know if you suspect Plague is possible. Healthcare providers should call the BCCDC Medical Microbiologist on-call for additional information.
Y. pestis is considered a high-risk pathogen in Canada which means the collection, transportation, and testing of suspect Y. pestis is highly regulated by biosafety procedures.
Treatment must begin as early in the stages of disease as possible and include antibiotics.
The fatality rate of untreated plague is 50 to 100 percent and 15 to 30 percent with treatment.
There is a vaccine for specific personnel who may be at heightened risk of infection. However, the vaccine can have significant side effects and is not available for the general public.
Flea and rodent control are essential, especially in endemic areas. Also, appropriate precautions around infected body fluids with bubonic plague, and respiratory discharges around individuals with plague pneumonia are required to prevent the spread of this disease, until at least 48 hours after the administration of antibiotics. Veterinary staff working with potentially infected animals should also take appropriate contact precautions.
Hunters, veterinarians, hikers, campers, biologists, owners of cats allowed to roam free and rural residents in areas where plague is detected are at increased risk of exposure. The risk of exposure to infected fleas is higher in areas near rodent colonies experiencing widespread mortality.
