Plague infection : symptoms and causes

Plague infection : symptoms and causes

Plague is an infectious disease caused by the bacteria Yersinia pestis, a zoonotic bacteria, usually found in small mammals and their fleas. Known as the Black Death during medieval times, today plague occurs in fewer than 5,000 people a year worldwide. It can be deadly if not treated promptly with antibiotics.

Plague is divided into three main types — bubonic, septicemic and pneumonic — depending on which part of your body is involved. Signs and symptoms vary depending on the type of plague.


Bubonic plague

Bubonic plague is the most common variety of the disease. It’s named after the buboes — swollen lymph nodes — which  typically develop within a week after an infected flea bites you.

Buboes may be:

Situated in the groin, armpit or neck
About the size of a chicken egg
Tender and warm to the touch

Other signs and symptoms may include:

Sudden onset of fever and chills
Fatigue or malaise
Muscle aches

Pneumonic plague

Pneumonic plague affects the lungs. It’s the least common variety of plague but the most dangerous, because it can be spread from person to person via cough droplets. Signs and symptoms can begin within a few hours after infection, and may include:

Cough, with bloody sputum
Difficulty breathing
Nausea and vomiting
High fever

Pneumonic plague progresses rapidly and may cause respiratory failure and shock within two days of infection. If antibiotic treatment isn’t initiated within a day after signs and symptoms first appear, the infection is likely to be fatal.

What causes Plague

The bacterium (Yersinia pestis) that cause plague can be transmitted from a host such as a rat to a human through the bite of an animal or insect (such as a flea). These bites transport the zoonotic disease. The animal or insect that spreads the disease is referred to as a vector. More than 200 different rodents and other species can serve as hosts. Hosts can include domestic cats and dogs, squirrels, chipmunks, marmots, deer mice, rabbits, hares, rock squirrels, camels, sheep, and other animals.

The vector is usually the rat flea. Thirty different flea species have been identified as vectors of the plague. Other vectors of plague include ticks and human lice. Transmission can also occur when someone inhales plague-infected organisms that have been released into the air. Plague can be aerosolized, as in acts of terrorism, causing the inhalation (pneumonic) form of the disease. People infected with pneumonic plague can also transmit airborne plague through coughed droplets of their own respiratory fluid. Close contact with plague-infected tissue or fluid can also transmit plague-causing bacteria to humans.


Complications of plague may include:

Death. Most people who receive prompt antibiotic treatment survive bubonic plague. Untreated plague has a high fatality rate.

Gangrene. Blood clots in the tiny blood vessels of your fingers and toes can disrupt the flow of blood and cause that tissue to die. The portions of your fingers and toes that have died may need to be amputated.

Meningitis. Rarely, plague may cause inflammation of the membranes surrounding your brain and spinal cord (meningitis).


Although no effective vaccine is available, scientists are working to develop one. Antibiotics can help prevent infection if you’re at risk of or have been exposed to plague.

Take the following precautions if you live or spend time in regions where plague outbreaks occur:

Rodent-proof your home. Remove potential nesting areas, such as piles of brush, rock, firewood and junk. Don’t leave pet food in areas that rodents can easily access.

Keep your pets free of fleas. Ask your veterinarian which flea-control products will work best.

Wear gloves. When handling potentially infected animals, wear gloves to prevent contact between your skin and harmful bacteria.

Use insect repellent. Closely supervise your children and pets when spending time outside in areas with large rodent populations. Use insect repellent.