Plague

Plague is an infectious disease of animals and people caused by the bacterium Yersinia pestis. While the name might cause alarm, things have changed since millions of Europeans died from the disease during the Middle Ages. Today, plague is considered a rare disease overall, although the bacteria naturally circulate in wild rodents and fleas in certain parts of the world. In the U.S., plague is predominantly found in rural and semirural areas of the West, especially where wild rodents and their fleas are abundant. The majority of human and animal cases occur in Arizona, California, Colorado, and New Mexico.

All mammals are potentially susceptible to plague. However, their vulnerability to severe disease and their role in spreading it vary widely. Severe disease is most often seen in wild rodents like prairie dogs, chipmunks, and squirrels. Less often, it surfaces in wild rabbits (especially cottontails), pet cats, and, rarely, people. Although pet dogs also can catch plague or plague-carrying fleas, they are more resistant to getting sick.

What are the signs of plague?

There are three main forms of plague—all caused by the same bacterium. The form that develops depends on how the bacterium is spread, how it enters the body, and where the infection is focused. Cats can have all three forms of plague. Dogs are largely resistant to illness, and those that do become sick tend to have milder signs.

Bubonic plague

This is the most common form in animals, and it can develop following a flea bite or entry of bacteria through the skin. 

Common signs of bubonic plague include:

  • Fever
  • Lethargy
  • Swollen and painful lymph nodes (buboes), usually under the jaw or around the neck
  • Loss of appetite

Cats—Cats also may develop eye discharge, mouth sores, ruptured skin abscesses, diarrhea, vomiting, spleen and liver damage, and pneumonia. Infections can be deadly: in experimental studies, about half of infected cats did not survive the infection.

Rodents—Bubonic plague can take different forms in rodents. In the acute form, rodents develop bleeding buboes as well as an enlarged spleen, but no other internal damage. Death typically occurs within 3 to 5 days. In the subacute form, rodents develop rotting buboes and internal damage, with death occurring in 6 or more days. Both forms cause bleeding from the nose, tiny red or purple spots on the skin (petechiae), abscess formation, and lung inflammation (pneumonitis). 

Pneumonic plague

Pneumonic plague—the most contagious form—typically is spread through respiratory droplets, and can be fatal if not promptly treated. It occurs when the Y. pestis bacteria infect the lungs, either directly (as through inhalation) or as a progression from septicemic or bubonic forms. Cats are highly susceptible, and often develop severe illness. 

Common signs of pneumonic plague include:

  • Fever
  • Coughing or sneezing
  • Labored or rapid breathing
  • Open-mouth breathing (especially cats)
  • Eye or nose discharge (may be bloody or pus-like)

Vomiting or diarrhea also may be present, especially in cats. Note that cats with pneumonic plague are known sources of infection in people, including both pet owners and veterinary professionals.

Septicemic plague

Septicemic plague occurs when Y. pestis bacteria enter the bloodstream, either directly (as through a fleabite or wound) or as a complication of bubonic or pneumonic plage. There, the bacteria rapidly multiply, releasing toxins that trigger widespread inflammation, coagulation disorders, and organ failure.

Signs can mimic those of other illnesses, making diagnosis challenging without laboratory testing. They include:

  • Sudden high fever
  • Lethargy, weakness, or depression
  • Loss of appetite
  • Vomiting or diarrhea
  • Rapid heart rate
  • Circulatory signs (like hypothermia or shock)
  • Hemorrhagic signs (like petechiae, bruising, or bleeding from the nose, gums, or rectum)

Some animals also may have neurologic signs like seizures and uncoordinated movements. Death may occur rapidly, sometimes with no warning—especially in cats, rabbits, and rodents.

What should I do if I suspect plague?

Many of the described signs of plague require immediate veterinary attention, and the disease can be highly contagious. Your fast action can protect both your pet(s) and your family.

If your pet has any of the listed signs, contact your veterinarian right away so they can advise you on next steps and prepare for your visit. Be sure to tell your veterinarian about any possible exposures to wild rodents or fleas.

In the meantime:

  • Avoid close contact (no kissing, snaggling, or sleeping together), especially if your pet has sores or is coughing or sneezing.
  • Refrain from touching their sores or body fluids.
  • Wash your hands thorough after handling you pet or anything they’ve touched
  • Wear gloves and a mask if you must handle them closely
  • Keep them away from other pets and people
  • Avoid trying to treat your pet yourself

How is plague diagnosed and treated?

  • Your veterinarian may suspect plague based on your pet’s signs and their likelihood of exposure to wild rodents or fleas—especially in areas where plague is known to occur. Buboes are a strong diagnostic clue when present, but lymph node enlargement may be absent in cases of pneumonic or septicemic plague.
  • To confirm the diagnosis, your veterinarian will collect samples from your pet, such as bubo fluid, blood, and/or nose or mouth swabs, and send them to a laboratory to test for Y. pestis bacteria or antibodies against the bacteria. This is often done in coordination with state public health authorities, who can help with rapid testing, assess potential exposures, recommend steps to prevent further spread. Depending on your pet’s signs, your veterinarian also may recommend lung X-rays to check for signs of pneumonia.
  • Plague is treatable with antibiotics, and early treatment can be lifesaving. The choice, administration route, and dose of antibiotic depend on the severity of disease and species of animal, and may be adjusted based on your pet’s age, size, and health status. Your veterinarian may start treatment immediately, before plague is confirmed.
  • Except in severe cases, animals generally respond quickly to antibiotics and have a good chance of recovery. For at-home treatment, it is critical that antibiotics be given exactly as directed. Animals generally are considered noninfectious after 48 to 72 hours of antibiotic therapy, provided their condition is improving.
  • In more serious cases, animals may require additional care like IV fluids, oxygen therapy, and nutritional support along with close monitoring in the hospital or at home.
  • Animals suspected or confirmed to have plague often need to be isolated during treatment—especially if they have the pneumonic form—to prevent the disease from spreading to other animals and people. Veterinary professionals caring for plague patients will take additional precautions to protect themselves, including use of personal protective equipment (like gloves, disposable gowns, face shields or goggles, and masks or N95 respirators).

How is plague spread?

Wild rodents are the main reservoir of Y. pestis, meaning they maintain the bacteria in nature and play a key role in its transmission cycle. A major transmission route for animals and people is fleabites. The disease also can spread through: 

  • Direct contact with infected animals or their tissues, as may occur by handling sick or dead rodents or rabbits
  • Ingestion of infected animals, as when cats prey on rodents or rabbits
  • Inhalation of respiratory droplets from a person or animal (typically cats) with the pneumonic form of the disease

How can I protect my pet and others against plague?

Prevention of plague starts with two key steps: controlling fleas and avoiding contact with rodents. Animals that roam freely are more likely to encounter plague-infected animals or fleas—and could bring the disease home.

These tips can help keep everyone safe, and prevent many other infectious diseases, too:

  • Use year-round, veterinarian-recommended flea prevention for pets.
  • Check pets regularly for fleas, especially after they’ve been outdoors.
  • Keep pets away from wild animals and areas where sick or dead rodents or rabbits have been seen.
  • Keep cats indoors and supervise dogs when outdoors.
  • Avoid areas with known plague activity, and keep pets from roaming freelly in high-risk environments.
  • Rodent-proof your home and yardm such as by storing firewood away from the house and keeping tall grass and brush trimmed.
  • If you live in or travel to an area where plague occurs, ask your veterinarian about extra precautions, especially if your pet goes outdoors or interacts with wildlife (as when hunting).