Plague is a serious illness caused by a germ called Yersinia pestis. The germs mostly live in small rodents and their fleas. The most common way for humans to get plague is a flea bite.
Plague is a rare disease. The illness mostly occurs in only a few countries around the world. In the United States, plague affects a few people each year in rural or semirural areas of western states.
Plague usually can be treated with antibiotics. If not treated, the illness is often deadly.
Plague is considered a potential bioweapon. The U.S. government has plans and treatments in place if the disease is used as a weapon.
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There are three types of plague. The symptoms vary for each type.
Bubonic plague causes swelling of lymph nodes. These are small, bean-shaped filters in the body's immune system. A swollen lymph node is called a bubo. The word "bubonic" is describing this feature of the disease.
If a person has bubonic plague, buboes appear in the armpits, groin or neck. Buboes are tender or painful. They vary in size from about less than half an inch (1 centimeter) to about 4 inches (10 centimeters).
Other symptoms of bubonic plague may include:
- Sudden high fever and chills.
- Not feeling well in general.
- Muscle aches.
- Rarely, skin sores.
Septicemic plague occurs when plague bacteria multiply in the bloodstream. Buboes may not be present.
Early symptoms are very general and include:
- Sudden high fever and chills.
- Extreme weakness.
- Stomach pain, diarrhea and vomiting.
More-serious symptoms may develop with advanced disease and organ failure. These include:
- Bleeding from the mouth, nose or rectum, or under the skin.
- Signs of shock, such as seizure, rash and low blood pressure.
- Blackening and death of tissue, called gangrene, most commonly on the fingers, toes, ears and nose.
Pneumonic plague affects the lungs. The disease may begin in the lungs, or it may spread from infected lymph nodes to the lungs. Symptoms can begin within a few hours after exposure and worsen rapidly.
Symptoms may include:
- Sudden high fever and chills.
- Cough, with bloody mucus.
- Difficulty or irregular breathing.
- Chest pain.
- Upset stomach and vomiting.
If treatment is not begun the first day, the disease progresses rapidly to failure of the lungs, shock and death.
When to see a doctor
Get immediate care if you have a sudden high fever.
Get emergency care if you have a sudden high fever or other symptoms and you live in an area that has had cases of plague. In the western United States, most cases have been in Arizona, California, Colorado and New Mexico.
Cases have occurred in Africa, Asia and Latin America. The countries with frequent cases include Madagascar, the Democratic Republic of Congo and Peru.
Plague is caused by a bacteria called Yersinia pestis. The bacteria circulate in populations of small animals and their fleas.
In the western United States, these animals include:
- Rats, mice and voles.
- Prairie dogs.
- Ground squirrels and chipmunks.
Other animals can get plague by eating small animals with the disease or picking up their fleas. These may include:
- Pet cats and dogs.
- Wild cats.
Disease in humans
People are most likely to get plague from a flea bite. The fleas are likely to come from small wild animals or from pets.
People also can get plague from direct contact with tissues of a sick animal. For example, a hunter can pick up the disease while skinning or handling an animal with the illness.
Pneumonic plague can be passed from animals to humans, or from humans to humans. Tiny droplets in the air can carry the bacteria when a person or animal coughs or sneezes. People can become infected when they inhale the droplets or touch coughed-up mucus.
The risk of getting plague is very low. Worldwide, only a few thousand people get plague each year. In the United States, seven people on average get plague each year.
Plague has been reported in nearly all parts of the world. The most common locations are Madagascar, the Democratic Republic of Congo and Peru. In Madagascar there is usually an outbreak of plague every year.
Plague has been reported in the western United States, most often in Arizona, California, Colorado and New Mexico.
The disease mostly survives in populations of rodents and their fleas in rural and semirural areas. It also has occurred in cities with overcrowding, poor sanitation or large rat populations.
People are at risk of getting plague if they work outdoors in areas where plague-carrying animals are common. People who work in animal clinics in these regions also have a risk of coming into contact with pet cats and dogs with the disease.
Camping, hunting or hiking in areas where plague-carrying animals reside can increase the risk of being bitten by an infected flea.
The U.S. government considers plague a possible biological weapon. Evidence exists of it being used or developed as a weapon in the past. The U.S. government has guidelines for treatment and prevention of plague used as a weapon.
Complications of plague may include:
- Gangrene. Blood clots can form in the tiny blood vessels of the fingers, toes, nose and ears. This can cause the tissues to die. The dead tissue needs to be removed.
- Meningitis. Rarely, plague may cause swelling and disease of the protective tissues surrounding the brain and spinal cord. This condition is called meningitis.
- Pharyngeal plague. Rarely, the disease can be present in the tissues behind the nasal cavity and mouth, called the pharynx. This is called pharyngeal plague.
The risk of death in people with all types of plague in the United States is around 11%.
Most people with bubonic plague survive with prompt diagnosis and treatment. Death is more likely with septicemic plague because it is difficult to diagnose and worsens rapidly. Treatment may unintentionally be delayed.
Pneumonic plague is severe and worsens rapidly. Risk of death is high if treatment doesn't begin within 24 hours after symptoms start.
No vaccine is available, but scientists are working to develop one. Antibiotics can help prevent infection if you were likely exposed to plague.
People with pneumonic plague are isolated during treatment to prevent the spread of disease. Health care workers must wear protective masks, gowns, gloves and eyewear when they treat someone with pneumonic plague.
Reducing the risk of exposure
If you live or spend time outdoors where plague occurs:
- Rodent-proof your home. Remove nesting areas for rodents, such as piles of brush, rock, firewood and junk. Don't leave pet food in areas that rodents can easily access. If you become aware of rodents living in your home, take steps to remove them.
- Protect your pets. Use flea-control medicines for your pets. Talk to your vet about the best options. If your pet is sick, get prompt treatment. Don't let pets sleep with you if they are outside in areas where plague occurs.
- Protection from animals. When handling dead animals, wear gloves to prevent contact between your skin and the animal. Call your local health department if you have concerns about the removal of a dead animal.
- Use insect repellent on skin and clothing. When outdoors, use insect repellents registered with the U.S. Environmental Protection Agency. These include products that contain DEET, picaridin, IR3535, oil of lemon eucalyptus (OLE), para-menthane-3,8-diol or 2-undecanone. Do not use a spray directly on your face. Do not use products with OLE or PMD on children under age 3. Do not use insect repellent on a child under 2 months old.