Yersinia pestis infection (patient information)

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Yersinia pestis infection


What are the symptoms?

What are the causes?

Who is at highest risk?

When to seek urgent medical care?


Treatment options

Where to find medical care for Yersinia pestis infection?

What to expect (Outlook/Prognosis)?

Possible complications

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: João André Alves Silva, M.D. [2]


Plague is an infectious disease that affects rodents, certain animals and humans. It is caused by the Yersinia pestis bacteria. These bacteria are found in many areas of the world, including the United States. There are 3 types of plague (bubonic, pneumonic and septicemic). Common symptoms of the disease include: fever, headache, chills, muscle pain, nausea and vomiting. The bubonic plague is characterized by swollen lymph nodes; the pneumonic plague by a rapid developing pneumonia; and the septic plague by bleeding and necrosis of tissues. People who live in rural areas, in contact with rodents are at higher risk of contracting the disease. The plague may be diagnosed by the signs and symptoms present in the patient and by laboratory culture of blood, sputum or lymph node aspirate. Complications may include: pneumonia, septicemia, shock and death. With adequate antibiotic treatment the mortality rate is about 8-10%.

What are the Symptoms of Yersinia Pestis Infection?

Plague symptoms depend on how the patient was exposed to the plague bacteria. The plague can take different clinical forms, but the most common are bubonic, pneumonic and septicemic.

Bubonic Plague

Symptoms appear suddenly, usually after 2 - 5 days of exposure to the bacteria, and may include:

  • Commonly found in the groin, but may occur in the armpits or neck, most often at the site of the infection (bite or scratch)
  • Pain may occur in the area before the swelling appears

Pneumonic Plague

Symptoms appear suddenly, typically 2 - 3 days after exposure, and may include:

Septicemic Plague

This type may cause death even before its symptoms occur. Symptoms may include:

What Causes Yersinia Pestis Infection?

Plague is caused by the bacteria Yersinia pestis. Rodents, such as rats, carry the disease. It is spread by their fleas.

The plague bacteria can be transmitted to humans by the following ways:

  • Flea bites
  • Plague bacteria are most often transmitted by the bite of an infected flea.
  • During plague epizootics, many rodents die, causing hungry fleas to seek other sources of blood.
  • People and animals that visit places where rodents have recently died from plague are at risk of being infected from flea bites.
  • Dogs and cats may also bring plague-infected fleas into the home.
  • Flea bite exposure may result in primary bubonic plague or septicemic plague.
  • Contact with contaminated fluids or tissues
  • Humans can become infected when handling tissue or body fluids of a plague-infected animal.
  • Infectious droplets
  • This type of spread has not been documented in the United States since 1924, but still occurs with some frequency in developing countries. Cats are particularly susceptible to plague and can be infected by eating infected rodents. Sick cats pose a risk of transmitting infectious plague droplets to their owners or to veterinarians. Several cases of human plague have occurred in the United States in recent decades as a result of contact with infected cats.

In the Middle Ages in Europe, massive plague epidemics killed millions of people. Plague can still be found in Africa, Asia, and South America. Today, plague is rare in the United States, but it has been known to occur in parts of California, Arizona, Colorado, and New Mexico.

The three most common forms of plague are:

The time between infection and development of symptoms is typically 2 to 7 days, but may be as short as 1 day for pneumonic plague. Risk factors for plague include a recent flea bite and exposure to rodents, especially rabbits, squirrels, or prairie dogs, or scratches or bites from infected domestic cats.

Who is at Highest Risk?

Human plague occurs in areas where the bacteria are present in wild rodent populations. The risks are generally highest in rural and semi-rural areas, including homes that provide food and shelter for various ground squirrels, chipmunks and wood rats, or other areas where you may encounter rodents.

People can get the plague when they are bitten by a flea that carries the plague bacteria from an infected rodent. People with highest risk of infection include:

  • People who handle infected animals
  • People are usually more at risk during, or shortly after, a plague epizootic
  • People that visit places where rodents have recently died from plague, because of the risk of being bitten by an infected flea
  • People who have cats that have the plague

When to Seek Urgent Medical Care?

People who should seek urgent medical care include:

  • Anyone who develops plague symptoms after exposure to fleas or rodents, especially if he/she lives in or has visited an area where plague occurs
  • Anyone who lives or has recently traveled to the western U.S. or any other plague endemic area and has symptoms suggestive of plague

People in close contact with very sick pneumonic plague patients may be evaluated and possibly placed under observation. Preventive antibiotic therapy may also be given, depending on the type and timing of personal contact.


The first step in plague diagnosis is evaluation by a health worker. Plague is a plausible diagnosis for people who are sick and live in, or have recently traveled to, the western United States, or any other plague-endemic area.

The most common sign of bubonic plague is the rapid development of a swollen and painful lymph node called a bubo. A known flea bite or the presence of a bubo may help a doctor to consider plague as a cause of the illness.

In many cases, particularly in septicemic and pneumonic plague, there are no obvious signs that indicate plague.

Diagnosis is made by taking samples from the patient, especially blood or part of a swollen lymph node, and submitting them for laboratory testing. Tests that may be done include:

Once the laboratory receives the sample, preliminary results can be ready in less than two hours. Laboratory confirmation will take longer, usually 24 to 48 hours.

Often, presumptive treatment with antibiotics will start as soon as samples are taken, if plague is suspected.

Treatment Options

Plague is a very serious illness, but is treatable with commonly available antibiotics. The earlier a patient seeks medical care and receives appropriate treatment for the plague, the better his/her chances of a full recovery.

People in close contact with very sick pneumonic plague patients may be evaluated and possibly placed under observation. Preventive antibiotic therapy may also be given, depending on the type and timing of personal contact.

People with the plague need immediate treatment. If treatment is not received within 24 hours after the first symptoms have developed, death may occur. Antibiotics that may be used to treat the plague include:

Oxygen, intravenous fluids, and respiratory support are usually also needed.

Patients with pneumonic plague should be strictly isolated from caregivers and other patients. People who have had contact with anyone infected by pneumonic plague should be watched carefully and given antibiotics as a preventive measure.

Where to Find Medical Care for Yersinia Pestis Infection?

Directions to Hospitals Treating Yersinia pestis infection

What to Expect (Outlook/Prognosis)?

Without treatment, about 50% of people with bubonic plague die. Almost all people with pneumonic plague die if not treated. Treatment reduces the mortality rates to 8-10%.

Possible Complications

Possible complications of human plague include:


Important measures to prevent plague infection include:

  • Reduce rodent habitat around your home, work place, and recreational areas. Remove brush, rock piles, junk, cluttered firewood, and possible rodent food supplies, such as pet and wild animal food. Make your home and outbuildings rodent-proof.
  • Wear gloves if you are handling or skinning potentially infected animals to prevent contact between your skin and the plague bacteria. Contact your local health department if you have questions about disposal of dead animals.
  • Use repellent if you think you could be exposed to rodent fleas during activities such as camping, hiking, or working outdoors. Products containing DEET can be applied to the skin as well as clothing and products containing permethrin can be applied to clothing (always follow instructions on the label).
  • Keep fleas off of your pets by applying flea control products. Animals that roam freely are more likely to come in contact with plague infected animals or fleas and could bring them into homes. If your pet becomes sick, seek care from a veterinarian as soon as possible.
  • Do not allow dogs or cats that roam free in endemic areas to sleep on your bed.


A plague vaccine is no longer available in the United States. New plague vaccines are in development, but are not expected to be commercially available in the immediate future.


World Health Organization (WHO)
Centers for Disease Control and Prevention (CDC)