How do people get plague?

In California, the most common way that people get plague is through the bite of infected fleas that live on wild rodents or in rodent burrows in the ground.

​People are more likely to come in contact with infected fleas when plague is spreading in a rodent population (this is called "epizootic plague"). Rodents may die when plague is active in a rodent population, and hungry fleas will leave a dead rodent to feed on other animals, including humans.

People can also get plague by:

• Contact with a​​nimal tissues, blood, or other body fluids infected with plague bacteria​

• Yersinia pestis in the blood and tissues of an infected animal (e.g., rodents) can enter a person’s body through cuts and scrapes in the skin or through the eyes, nose, or mo​​uth.

• Contact with droplets in the air from humans or animals (especially cats) that have a plague infection in their lungs​
  

• ​Yer​sinia pestis can be inhaled by others when an infected human or animal coughs or sneezes.​
  
  

​What are the symptoms of plague in people?

There are three types of plagu​e that people can get, and the symptoms can be different based on the type of plague or where in the body a person is infected:

1. Bubonic plague: Occurs when lymph nodes and glands, usually in the neck, armpits, and groin, beco​me infected and swollen with plague bacteria (these swollen glands are called "bubos"). Symptoms include fever, chills, headache, weakness, nausea, and vomiting. If not treated early, bubonic plague can lead to the two other types of plague (septicemic and pneumonic).

2. Septicemic plague: Occurs when the blood is infected with plague bacteria. Symptoms include high fever, extreme weakness, and bleeding into the skin and other organs.

3. Pneumonic plague: Occurs when the lungs are infected with plague bacteria. Symptoms include difficulty breathing, chest pain, cough, and bloody mucous.

If diagnose​​d early, plague can be treated successfully with ​antibiotics. Septicemic and pneumonic plague are the more severe forms of plague and are more difficult to treat. These forms can often cause death if antibiotic treatment is not started within the first 24 hours of illness.​​

Plague is an ancient disease that has caused epidemics of illness and the deaths of millions of people throughout history. During the “Black Death” of the 14th century, an estimated one-third of the population of Europe died from plague. Today, plague is rare among humans but is found each year among squirrels, chipmunks, and other rodents in California and the southwestern United States. 

People can become infected with plague bacteria if they are bitten by a flea from an infected rodent or have close contact with an infected animal. Most people with plague develop fever and swollen lymph nodes. Plague is treatable with antibiotics but can progress to severe and sometimes fatal illness if diagnosis and treatment are delayed. 

People visiting, hiking, camping, or living in areas where plague occurs should avoid contact with wild rodents and their fleas. Domestic cats are also susceptible to plague and can pass the infection to their owners.​

What do rodents have to do with plague?

The bacteria that cause plague are transmitted between wild rodents and their fleas. Fleas are infected with plague bacteria by feeding on the blood of infected rodents, and those fleas can then pass the plague bacteria onto uninfected rodents or animals, which can infect more fleas.

In California, rodents that sometimes carry plague bacteria include ground squirrels, chipmunks, and woodrats. Rats and mice in cities are not known to be involved in plague transmission in California today.​

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How can I help prevent plague?

The best way to reduce your chances of getting plague is to avoid contact with wild rodents and their fleas. You can observe rodents from a distance, but do not touch, feed, or handle any wild rodents. Make sure children are aware of and follow these rules. You can also help protect your pets from plague by keeping them away from rodent burrows and from approaching sick or dead rodents.

Other ways to help prevent plague:

• Be aware of areas where rodents infected with plague might be present – look for signs or postings in campgrounds that mention plague.
  

• Follow instructions on plague notices that are posted at campgrounds and recreation areas.

• Store food and garbage in rodent-proof containers to keep rodents away.

• Do not camp, rest, or sleep near rodent burrows.
  

• Wear long pants tucked into boots and use EPA-registered insect repellent on clothes and exposed skin to keep fleas from biting you.

• While camping or exploring in areas where plague has been reported, leave pets at home if possible. Otherwise, keep pets on a leash or in a closed-off area to prevent them from chasing or hunting rodents and sniffing in burrows.

• Protect pets with flea control products — for more information, talk to your veterinarian.

• Be careful when handling sick cats that may have had contact with wild rodents in plague areas. If your cat is sick, take it to the veterinarian for examination.

• If you live in a plague area, keep cats indoors if possible.​​