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Yersinia pestis in Cats

The parasitic genus Yersinia pestis causes the bacterial disease referred to as plague. This condition occurs worldwide. In the United States, it is predominantly found in the southwest between the months of May and October. Carriers of this disease include rats, squirrels and mice; the disease is typically transmitted when a rodent either bites, or is bitten by a cat.

The infection travels rapidly to the lymph nodes, where white blood cells are produced. The resulting reaction from the lymph nodes is a rapid multiplication of white cells, abnormal fluid build up with swelling, and possible skin breakage. Cats infected with plague will experience fever, inflammation, and excessive pain due to the lymph nodes being chronically swollen.

Outdoor cats are most affected, with males predominating due to their tendency to roam. However, there are no gender or breed boundaries for susceptibility to the plague.

Although it is quite rare, plague is transmittable to humans, and care should be taken to avoid fleas and body fluids from an animal that is suspected of being infected with the Yersinia bacterium.

Dogs may also be infected with plague. If you would like to learn more about how this disease affects dogs, please visit this page in the PetMD health library.

Symptoms and Types

There are three forms of plague: bubonic plague, pneumonic plague, and septicemic plague. Symptoms associated with bubonic plague in cats will include painfully swollen lymph nodes, fever, inflammation, depression, vomiting, dehydration, diarrhea, enlarged tonsils, and anorexia. The head and neck area will swell considerably, and should the cat survive, its lymph nodes may abscess and then rupture and drain. Other symptoms include discharge from the eyes, mouth ulcers, and a loss of appetite, with visible weight loss being evident. Coma may follow.

The normal incubation period for bubonic plague is between two and seven days after the cat has been bitten. In the case of pneumonic plague, a lung infection will occur; and with septicemic plague, which is rare in cats, the same symptoms as bubonic plague will appear, along with systemic infection of the blood.


The Yersinia bacterium is transmitted to cats when an infected flea bites them, or when they ingest an infected rodent. It is more common for a cat to become infected after eating a rodent than it is for the cat to acquire this disease through a fleabite.

Another possible cause for exposure could come from the animal’s environment. If the home is heavily infested with fleas, or if the homeowner resides near a wildlife habitat, where the animal is exposed to rodents, this could put the animal at a higher risk of contracting the plague. Garbage, woodpiles, and food sources can also be outlets for transmission of this disease.


Your veterinarian will run a full diagnostic evaluation on the cat, including blood samples, culture samples of fluids, and kidney and liver testing, in order to establish a definitive diagnosis of this disease. A swollen lymphatic system is a clear indication that infection is present and blood tests will show the level of white blood cells present, amongst other things, further aiding in identifying the presence of plague bacteria.

A thorough physical examination will be undertaken to check for swelling around the neck and head, liver and kidneys, and to check for signs of dehydration, fever, lung infection, or anything else that will conclusively pinpoint the plague as a cause for your cat’s illness.

Medication will be administered to treat the symptoms, and if plague is confirmed, or suspected, your cat will be isolated until the condition is resolved.

You will need to give a thorough history of your cat's health, including a background history of symptoms, and possible incidents that might have precipitated this condition.



Your cat will require hospitalization to treat the more severe symptoms of plague, and will be given a full course of antibiotics. Cats that are weakened and dehydrated, will require an intravenous drip to assist in rehydration. Flea treatment will also be required. The incidence of mortality is high for cats that are not treated early and effectively.

Living and Management

Ongoing flea control and management of rodents is a must. There is no home management plan for this disease, and all cases of suspected infection should be reported to your veterinarian immediately. However, maintaining a flea-free home and keeping rubbish, food, and woodpiles to a minimum will help greatly in reducing the risk of plague infection. Additionally, cats should be neutered, as this aids in subduing their hunting instinct.

Indoor cats are less likely to be exposed to the Yersinia bacterium. But if you do not have the option of keeping your pet indoors, you will need to provide preventive flea care to your cat.

When travelling to areas where the plague bacteria may be present, it is wise to make sure your cat is kept on a leash or in an enclosed environment at all times so that exposure to wild rodents or fleas that may be carrying this disease is limited.

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