December 2010

What Is Plague?

Plague is an infectious 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 rat. 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 – about 75% to 97% of all cases.
  • Pneumonic plague infects the lungs. It can spread through airborne droplets when infected people cough or sneeze, or through contact with infected body fluids such as blood or urine. It can also spread from clothing or linens that have been contaminated with infected body fluids. While pneumonic plague is the most deadly, it is the least common form (occurring in less than 14% of cases). There is concern that this form could be used in a bioterrorist attack.
  • Septicemic plague is when the infection spreads through the bloodstream. It accounts for less than 20% of all cases, and is typically fatal without antibiotics. Both bubonic and pneumonic plague can progress to septicemic plague.
X-ray scan of a flea showing the actual size of the plague virus
Xenopsylla cheopis (oriental rat flea). This flea is the primary carrier of plague.

Where Does Plague Occur?

Historically plague caused worldwide epidemics that led to millions of deaths. The most widely known plague epidemic was the Black Death of 14th century Europe. This was in a time when human homes and workplaces were inhabited by flea-infested rats. Outbreaks are a rare occurrence today due to improved living conditions, public health and antibiotic treatment.

Approximately 2,000 cases are reported to the World Health Organization each year, mostly from Africa, South America and Asia. About 10 – 15 cases of plague occur each year in the southwestern U.S.A; these cases are usually from contact with wild animals. Large outbreaks are rare.

What Are the Symptoms of Plague?

Symptoms usually occur one to 10 days after exposure. Initial symptoms are flu-like complaints: fever, chills, muscle pain, weakness and headache. A swollen and very tender lymph gland, accompanied by pain, is another symptom. Pneumonic plague symptoms: rapidly developing pneumonia with shortness of breath, chest pain, cough and sometimes bloody or watery sputum. The pneumonia may cause respiratory failure and shock. If left untreated, the person may die.

What Is the Treatment?

Antibiotics such as streptomycin, gentamicin and others are effective treatments for plague. People with pneumonic plague need to be placed in medical isolation so they do not pass it on to other people.

Is There a Vaccine for Plague?

Currently, there is no vaccine available for general public use. A vaccine for use in people at high risk of exposure, such as some military people and animal handlers in areas where plague is common, was discontinued in 1998. Although the vaccine was effective in preventing bubonic plague it did not prevent the pneumonic form and involved multiple injections, with many side effects. Research is ongoing to develop a new, more effective vaccine.

Can I Get Treatment If I Have Been Exposed but Do Not Have Symptoms?

Yes, you can take antibiotics if you may have been exposed to plague, or if you have been in close contact with people who are partially treated or untreated.

Can Plague Be Prevented?

To reduce the likelihood of being bitten by infected fleas where plague is known to occur:

  • Make homes, recreation places and workplaces less attractive to rodents, such as rats, by removing food sources, storing garbage safely, and eliminating nesting materials.
  • Use trained professional staff to inspect and, if necessary, fumigate warehouses, sheds or other buildings where there may be infected rodents.
  • Make sure your dog or cat is treated regularly for fleas and does not roam freely.

Avoid direct contact with disease-bearing animals, infected tissues, and contaminated clothing and linen so that plague does not spread.

More Information

Call Toronto Public Health at 416-338-7600 (TTY at 416-392-0658) or speak to your health care provider.