Plague: Definition, Manifestations and Treatment.


Plague is an infectious disease caused by bacteria called Yersinia pestis. These bacteria are found mainly in rodents, particularly rats, and in the fleas that feed on them. Other animals and humans usually contract the bacteria from rodent or flea bites.

SEM image of Yersinia pestis


Historically, plague destroyed entire civilizations. In the 1300s, the “Black Death,” as it was called, killed approximately one-third (20 to 30 million) of Europe’s population. In the mid-1800s, it killed 12 million people in China. Today, thanks to better living conditions, antibiotics, and improved sanitation, current World Health Organization statistics show there were only 2,118 cases in 2003 worldwide.

Approximately 10 to 20 people in the United States develop plague each year from flea or rodent bites primarily from infected prairie dogs in rural areas of the southwestern United States. About 1 in 7 of those infected die from the disease. There has not been a case of person-to-person infection in the United States since 1924.


Most cases of plague reported are from developing countries such as Africa and Asia. During 1990-1995, a total of 12,998 cases of plague were reported to the World Health Organization (WHO), particularly from countries such as India, Zaire, Peru, Malawi, and Mozambique. The following countries reported more than 100 cases of plague: China, Congo, India, Madagascar, Mozambique, Myanmar, Peru, Tanzania, Uganda, Vietnam, and Zimbabwe. Several foci are located in the semi-arid regions of northeastern Brazil, and outbreaks have also been reported from Malawi and Zambia. Australia is the only continent that is considered free of plague. The largest enzootic plague area is in North America-the southwestern United States and the Pacific coastal area.

Types of plague

There are three basic forms of plague:

Bubonic plague

In bubonic plague, the most common form, bacteria infect the lymph system and become inflamed. (The lymph or lymphatic system is a major component of your body’s immune system. The organs within the lymphatic system are the tonsils, adenoids, spleen, and thymus). Bubonic plague is the most commonly occurring type of plague and is characterized by the appearance of buboes swollen, tender lymph nodes, typically found in the armpits and groin

It’s usually contracted when an infected rodent or flea bites you. In very rare cases, you can get the bacteria from material that has come into contact with an infected person. Bubonic plague infects your lymphatic system (the immune system), causing inflammation. Untreated, it can move into the blood and cause septicemic plague, or to the lungs, causing pneumonic plague.

Septicemic Plague

When the bacteria enter the bloodstream directly and multiply there, it’s known as septicemic plague. You usually get septicemic plague the same way as bubonic plague through a flea or rodent bite. You can also get septicemic plague if you had untreated bubonic or pneumonic plague. Symptoms include fever, chills, weakness, abdominal pain, shock, and bleeding underneath the skin or other organs. Buboes, however, do not develop.

Pneumonic Plague

When the bacteria spread to the lungs, you have pneumonic plague the most lethal form of the disease. When someone with pneumonic plague coughs, the bacteria from their lungs are expelled into the air. Other people who breathe that air can also develop this highly contagious form of plague, which can lead to an epidemic. Pneumonic plague is the only form of the plague that can be transmitted from person to person.


The plague bacteria, Yersinia pestis, is transmitted to humans when they are bitten by fleas that have previously fed on infected animals, such as:

  • Rats
  • Squirrels
  • Rabbits
  • Prairie dogs
  • Chipmunks

The bacteria can also enter your body if you have a break in your skin that comes into contact with an infected animal’s blood. Domestic cats and dogs can become infected with plague from flea bites or from eating infected rodents.

Pneumonic plague, which affects the lungs, is spread by inhaling infectious droplets coughed into the air by a sick animal or person.

Risk factors

The risk of developing plague is very low. Worldwide, only a few thousand people develop plague each year. However, your risk of plague can be increased by where you live and travel, your occupation, and even by some of your hobbies.


Plague outbreaks are most common in rural and semirural areas characterized by overcrowding, poor sanitation and a high rodent population.


Veterinarians and their assistants have a higher risk of coming into contact with domestic cats and dogs that may have become infected with plague. Also at higher risk are people who work outdoors in areas where plague-infected animals are common.


Camping, hunting or hiking in areas where plague-infected animals reside can increase your risk of being bitten by an infected flea.


Signs and symptoms vary depending on the type of plague.

Bubonic plague: 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
  • Headache
  • Fatigue or malaise
  • Muscle aches

Septicemic plague: Signs and symptoms include:

  • Fever and chills
  • Extreme weakness
  • Abdominal pain, diarrhea and vomiting
  • Bleeding from your mouth, nose or rectum, or under your skin
  • Shock
  • Blackening and death of tissue (gangrene) in your extremities, most commonly your fingers, toes and nose

Pneumonic plague 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
  • Headache
  • Weakness


Complications of plague may include:

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


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


  • Doctor performs certain blood tests such as cultures (growing the bacteria in the lab from samples of blood, sputum, and fluid from the bubo). Cultures require more than 48 hours to produce definitive results.
  • A doctor may order an X-ray film of the chest, especially to see if plague has infected the lungs.

Treatment and management

Treatment usually involves strong and effective antibiotics, intravenous fluids, oxygen, and sometimes breathing support. People with pneumonic plague must be isolated from other patients. Medical personnel and caregivers must take strict precautions to avoid getting or spreading plague.


As soon as your doctor suspects that you have plague, you’ll need to be admitted to a hospital. There, you’ll receive powerful antibiotics, such as:

  • Gentamicin
  • Doxycycline (Vibramycin)
  • Ciprofloxacin (Cipro)
  • Levofloxacin (Levaquin)

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