The plague is a serious bacterial infection that can be deadly. Sometimes referred to as the “black plague,” the disease is caused by a bacterial strain called Yersinia pestis. This bacterium is found in animals throughout the world and is usually transmitted to humans through fleas.

The risk of plague is highest in areas that have poor sanitation, overcrowding, and a large population of rodents.

In medieval times, the plague was responsible for the deaths of millions of people in Europe.

Today, there are only 1,000 to 2,000 cases reported worldwide each year, with the highest incidence in Africa.

Plague is a rapidly progressing disease that can lead to death if untreated. If you suspect you have it, call a doctor right away or go to an emergency room for immediate medical attention.

There are three basic forms of plague:

Bubonic plague

The most common form of plague is bubonic plague. 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 (a part of the immune system), causing inflammation in your lymph nodes. Untreated, it can move into the blood (causing 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. When they’re left untreated, both bubonic and pneumonic plague can lead to septicemic plague.

Pneumonic plague

When the bacteria spread to or first infect the lungs, it’s known as 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.

People usually get plague through the bite of fleas that have previously fed on infected animals like mice, rats, rabbits, squirrels, chipmunks, and prairie dogs. It can also be spread through direct contact with an infected person or animal or by eating an infected animal.

Plague can also spread through scratches or bites of infected domestic cats.

It’s rare for bubonic plague or septicemic plague to spread from one human to another.

People infected with the plague usually develop flu-like symptoms two to six days after infection. There are other symptoms that can help distinguish the three forms of the plague.

Bubonic plague symptoms

Symptoms of bubonic plague generally appear within two to six days of infection. They include:

  • fever and chills
  • headache
  • muscle pain
  • general weakness
  • seizures

You may also experience painful, swollen lymph glands, called buboes. These typically appear in the groin, armpits, neck, or site of the insect bite or scratch. The buboes are what give bubonic plague its name.

Septicemic plague symptoms

Septicemic plague symptoms usually start within two to seven days after exposure, but septicemic plague can lead to death before symptoms even appear. Symptoms can include:

  • abdominal pain
  • diarrhea
  • nausea and vomiting
  • fever and chills
  • extreme weakness
  • bleeding (blood may not be able to clot)
  • shock
  • skin turning black (gangrene)

Pneumonic plague symptoms

Pneumonic plague symptoms may appear as quickly as one day after exposure to the bacteria. These symptoms include:

  • trouble breathing
  • chest pain
  • cough
  • fever
  • headache
  • overall weakness
  • bloody sputum (saliva and mucus or pus from the lungs)

Plague is a life-threatening disease. If you have been exposed to rodents or fleas, or if you have visited a region where plague is known to occur, and you develop symptoms of plague, contact your doctor immediately:

  • Be prepared to tell your doctor about any recent travel locations and dates.
  • Make a list of all over-the-counter medications, supplements, and prescription drugs you take.
  • Make a list of people who have had close contact with you.
  • Tell your doctor about all your symptoms and when they first appeared.

When you visit the doctor, emergency room, or anywhere else where others are present, wear a surgical mask to prevent the spread of the disease.

If your doctor suspects you may have plague, they will check for the presence of the bacteria in your body:

  • A blood test can reveal if you have septicemic plague.
  • To check for bubonic plague, your doctor will use a needle to take a sample of the fluid in your swollen lymph nodes.
  • To check for pneumonic plague, fluid will be extracted from your airways by a tube that is inserted down your nose or mouth and down your throat. This is called a bronchoscopy.

The samples will be sent to a laboratory for analysis. Preliminary results may be ready in just two hours, but confirmatory testing takes 24 to 48 hours.

Often, if the plague is suspected, your doctor will begin treatment with antibiotics before the diagnosis is confirmed. This is because the plague progresses rapidly, and being treated early can make a big difference in your recovery.

The plague is a life-threatening condition that requires urgent care. If caught and treated early, it’s a treatable disease using antibiotics that are commonly available.

With no treatment, bubonic plague can multiply in the bloodstream (causing septicemic plague) or in the lungs (causing pneumonic plague). Death can occur within 24 hours after the appearance of the first symptom.

Treatment usually involves strong and effective antibiotics such as gentamicin or ciprofloxacin, 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.

Treatment is continued for several weeks after fever resolves.

Anyone who has come into contact with people with pneumonic plague should also be monitored, and they’re usually given antibiotics as a preventive measure.

Plague can lead to gangrene if blood vessels in your fingers and toes disrupt blood flow and cause death to tissue. In rare cases, plague can cause meningitis, an inflammation of membranes that surround your spinal cord and brain.

Getting treatment as quickly as possible is crucial to stop the plague from becoming deadly.

Keeping the rodent population under control in your home, workplace, and recreation areas can greatly reduce your risk of getting the bacteria that causes plague. Keep your home free from stacks of cluttered firewood or piles of rock, brush, or other debris that could attract rodents.

Protect your pets from fleas using flea control products. Pets that roam freely outdoors may be more likely to come into contact with plague-infected fleas or animals.

If you live in an area where the plague is known to occur, the CDC recommends not allowing pets that roam freely outside to sleep in your bed. If your pet becomes sick, seek care from a veterinarian right away.

Use insect repellent products or natural insect repellants (like oil of lemon eucalyptus) when spending time outdoors.

If you have been exposed to fleas during a plague outbreak, visit your doctor immediately so your concerns can be addressed quickly.

There is currently no commercially available vaccine against plague in the United States.

Epidemics of plague killed millions of people (about one-quarter of the population) in Europe during the Middle Ages. It came to be known as the "black death."

Today the risk of developing plague is quite low, with only 3,248 cases and 584 deaths reported to the World Health Organization (WHO) from 2010 to 2015.

Outbreaks are generally associated with infested rats and fleas in the home. Crowded living conditions and bad sanitation also increase the risk of plague.

Today, most human cases of the plague occur in Africa though they do appear elsewhere. The countries in which the plague is most common are Madagascar, the Democratic Republic of Congo, and Peru.

The plague is rare in the United States, but the disease is still sometimes found in the rural southwest and, in particular, in Arizona, Colorado, and New Mexico. The last epidemic of plague in the United States occurred in 1924 to 1925 in Los Angeles.

In the United States, reported cases average seven per year. Most have been in the form of the bubonic plague. There hasn’t been a case of person-to-person transmission of the plague in U.S. urban areas since 1924.