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Plague is a life-threatening infection caused by the organism Yersinia pestis. There are three types of plague. Bubonic plague is the most common type in humans. Infected fleas transmit Y. pestis primarily among rodents. When an outbreak kills many rodents, infected fleas can jump to other animals and humans, spreading the infection. Improved living conditions and health services have made human outbreaks uncommon, but occasional plague cases occur. Concern exists about the use of plague as a biological weapon. Plague bacteria could be put into a form that might be sprayed through the air, infecting anyone inhaling it and causing pneumonic plague. This form affects your lungs and can spread from person to person. Fortunately, when given promptly, antibiotics usually effectively treat plague.

Complications of Plague

Complications of plague may include:

  • Gangrene of your fingers and toes resulting from clots in the small blood vessels of your extremities
  • Severe shock
  • Sudden, severe lung failure (acute respiratory distress syndrome, or ARDS)
  • Bloodstream infection (septicemia)
  • Inflammation of the membranes and fluid surrounding your brain and spinal cord (meningitis)
  • Death

With prompt treatment, the overall fatality rate from plague is less than 15 percent. Without treatment, mortality rates can be as high as 60 percent for bubonic plague and 100 percent for pneumonic plague. Death can occur within days after symptoms first appear if treatment doesn't begin promptly.

Causes of Plague

Plague has afflicted humans throughout history. The cause of plague, the Yersinia pestis bacterium, was discovered in 1894 by Alexandre Yersin. Soon after, scientists realized that fleas transmitted the bacteria. Three types of plague exist.

Bubonic plague

Bubonic plague is the most common type of plague in humans. It's usually caused by a bite from an infected flea. Y. pestis bacteria primarily infect animals such as squirrels, rabbits and prairie dogs. You may become infected by a fleabite if you're in close contact with such animals. The bacteria can also enter through a cut in your skin if you handle these animals. Domestic cats that come into contact with infected animals also may transmit the infection to humans.

Septicemic plague

Septicemic plague occurs when plague bacteria multiply in your bloodstream. This happens when bacteria transmitted by a fleabite enter directly into your bloodstream, or as a complication of bubonic or pneumonic plague.

Pneumonic plague

Secondary pneumonic plague can develop if you're infected with another type of plague. In this case, the infection spreads to your lungs, causing a virulent pneumonia that can often be fatal. Primary pneumonic plague can occur when you inhale droplets coughed into the air by a person or animal with pneumonic plague.

Plague as a bioterrorism agent

Plague is also one of a number of potential agents of bioterrorism, along with anthrax, smallpox, botulism, tularemia and nerve gases. It's possible that plague bacteria could be turned into an aerosol and then be spread over large populations.

Signs & Symptoms of Plague

There are three types of plague: bubonic, septicemic and pneumonic. Signs and symptoms vary depending on the type of plague. It's possible to develop more than one type.

Bubonic plague

Signs and symptoms of bubonic plague generally appear within two to eight days of a plague-infected fleabite. After you're bitten, the bacteria travel through your lymphatic system, infecting the first lymph node they reach. The resulting enlarged lymph node (bubo) is usually 1 to 10 centimeters in diameter, swollen, painful and warm to the touch. It can cause so much pain that you can't move the affected part of your body. The bubo usually develops in your groin, but may also appear in your armpit or neck, depending on where the flea bit you.

Signs and symptoms of bubonic plague include:

  • Buboes — swollen, painful, warm lymph nodes
  • Sudden onset of fever and chills
  • Headache
  • Fatigue or malaise
  • Muscle aches

Septicemic plague

Septicemic plague occurs when plague bacteria multiply in your bloodstream. If septicemic plague occurs as a complication of bubonic plague, buboes may be present.

Signs and symptoms include:

  • Fever and chills
  • 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

Pneumonic plague — which can occur as a complication of another type of plague or by inhaling infectious droplets coughed into the air by a person or animal — is the least common form of plague. But it's also the most rapidly fatal. Early signs and symptoms, which generally occur within a few hours to a few days after inhaling contaminated droplets, include:

  • High fever
  • Weakness
  • Signs of pneumonia, including chest pain, difficulty breathing and a cough with bloody sputum
  • Nausea and vomiting

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.

Diagnosis of Plague

Your doctor may suspect plague if you live in a high-risk region or report a suspicious exposure. With the exception of a visible bubo, signs and symptoms often mimic other, much more common infectious diseases.

Medical history

You'll likely be asked to describe the type and severity of your symptoms and tell your doctor about your recent history, including whether you've been exposed to sick animals or traveled to areas with plague.

Bubo and respiratory fluid examination

If plague is suspected, your doctor may confirm the diagnosis through microscopic examination of fluid extracted from your bubo, bronchi or trachea. Needle aspiration is used to obtain fluid from your bubo. Fluid is extracted from your airways using endoscopy. In this procedure, a thin, flexible tube is inserted through your nose or mouth and down your throat. A suction device is sent down the tube to extract a fluid sample from your airways.

Blood test

Your doctor may also test blood drawn from your veins to diagnose plague. Y. pestis bacteria generally are present in your bloodstream only if you have septicemic plague.

Treatments of Plague

Treatment for plague includes antibiotics and supportive therapy. Your doctor is required by law to report documented plague infections to local health officials.


As soon as your doctor suspects that you have plague, you'll need to be admitted to an isolation room in a hospital. There, you'll receive powerful antibiotics directly into your veins (intravenously) or your muscles (intramuscularly) for seven to 10 days. Streptomycin and gentamicin are the most effective drugs against plague. Other alternatives include intravenous doxycycline (Vibramycin) and chloramphenicol (Chloromycetin).

Even if you don't have signs or symptoms, you'll need treatment with preventive, oral antibiotics for seven days after direct exposure to a person with pneumonic plague.

Supportive therapies

If you have serious complications, such as bleeding, organ failure and respiratory distress, then respiratory support, intravenous fluids and oxygen may be necessary.

Prevention of Plague

Although no effective vaccine is available, antibiotics offer effective preventive therapy if you're at risk of or have been exposed to plague. Ask your doctor immediately about preventive antibiotics if you:

  • Have had close contact with a person or animal with known or suspected pneumonic plague
  • Have been bitten by a flea or unknown insect in an area known to have recent plague cases
  • Are planning to spend time in a region with recent plague outbreak

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

  • Avoid contact with sick or dead animals. If you hunt, wear gloves when handling dead animals.
  • Rodent-proof your home. Remove potential nesting areas, such as piles of brush, rock, firewood and junk. Don't leave pet or bird food or any other foods in areas that rodents can easily access.
  • Prevent your pets from contracting fleas. Use flea-control products and don't allow pets to wander unsupervised. Ask your veterinarian for recommended flea-control brands and guidelines.
  • Take precautions when outdoors. Closely supervise your children and pets when spending time outside in areas with large rodent populations. Use insect repellent on your skin and clothing.

Know the risk factors and the symptoms of plague so that you can identify it early and contact your doctor immediately. If you know of recent plague cases in your area, report sick or dead animals to your local health department or to police.

When to seek Medical Advice

Call your doctor if you or someone close to you develops signs or symptoms of plague within a week of any of the following:

  • Being exposed to sick or dead rats, wild rabbits, squirrels and other rodents or to domestic cats that may have been exposed to such animals
  • Being bitten by a flea
  • Spending time in an area with a known, recent plague outbreak or with a large number of dead or dying animals
  • Having close contact — within six feet — with a person or animal with pneumonic plague
  • Traveling to a high-risk region of the United States or another country with high plague rates

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