Last Reviewed: December 2016

What is plague?

Plague is a severe disease that affects humans and other mammals caused by an infection with a type of bacteria, Yersinia pestis. Plague occurs naturally in the western United States and is transmitted by the bite of an infected flea, by handling infected animals, or inhaling droplets from the cough of an infected person or animal. Plague in humans can require strict isolation and disinfection procedures for infected individuals. The disease is rare in the United States, with an average of seven cases reported each year. Exposure to plague is typically limited to the western and southwestern parts of the country.

Who gets plague?

People working in or visiting areas with infected rodents (such as mice, rats, or squirrels) are at greater risk of getting this disease. There have been no reports of plague in New York State. However, exposures in the western U.S. or overseas have occasionally resulted in cases or need for investigations in the eastern U.S. Cases reported in the U.S. most often occur in late spring to early fall.

How is plague spread?

The most common way that plague is spread to people is by the bite of an infected flea. Other important ways it spreads includes the handling of infected animals (especially cats, rabbits, rats, mice, and squirrels), inhaling droplets from humans or household pets with plague, or by laboratory exposure. It can be spread from one person to another when an infected person coughs and releases droplets that can infect others. Typically, this requires direct and close contact with the person with plague.

What are the symptoms of plague and when do they appear?

While there are different forms of plague, fever, chills, headache, and weakness are symptoms of all forms and usually begin 1 to 6 days after exposure to the plague bacteria.

In bubonic plague, which is the most common form, one or more swollen, inflamed, tender, and painful lymph nodes (called buboes) develop in the body near where the infected flea bit the person.

In septicemic plague, plague bacteria infects the bloodstream. It causes symptoms of stomach pain, shock, and possibly bleeding into the skin and organs. Skin and other tissues, such as fingers and toes, may turn black and die. Septicemic plague can occur as the first symptom of infection or may occur if bubonic plague is left untreated.

In pneumonic plague, infection occurs in the lungs. This is the most serious form and may cause shortness of breath, chest pain, cough, respiratory failure, and shock may develop. Pneumonic plague develops when infectious droplets are inhaled or may progress from bubonic and septicemic plague.

How is plague diagnosed?

If plague is suspected, samples of blood, sputum (spit/mucous mix from a cough), or lymph node glands may be taken for laboratory testing. The laboratory tests will show if there is evidence of the bacteria, which can lead to a diagnosis.

What is the treatment for plague?

Plague can be treated successfully with intravenous antibiotics if appropriate therapy is started early. The duration of treatment is generally 10-14 days. If a person diagnosed with bubonic plague is not treated promptly, the bacteria can spread to other parts of the body and cause septicemic or pneumonic plague.

Does past infection with plague make a person immune?

There is no vaccine to prevent plague. Immunity after plague recovery is variable and may not provide complete protection.

What can be done to prevent the spread of plague?

  • Wear gloves if skinning or handling potentially infected animals to prevent contact between the skin and the plague bacteria.
  • If a person is exposed to someone diagnosed with some forms of plague he or she may be given antibiotics.
  • When human or animal cases have been identified in your community, take steps to reduce rodent habitats. This may include brush or junk removal, removal of rodent food supplies such as pet and wild animal food, and making home and outbuildings rodent-proof.
  • Do not allow dogs or cats that roam free in areas where plague occurs to sleep on your bed.
  • Apply flea control products to pets.
  • Use flea repellent products containing DEET during activities such as camping, hiking, or working outdoors in areas where plague is endemic.
  • Wild rodents such as prairie dogs imported from the western U.S. should not be kept as pets.