Merck Manual

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Pet Owner Version

Plague in Dogs


Paul Ettestad

, DVM, MS, Epidemiology and Response Division, New Mexico Department of Health

Reviewed/Revised Jun 2018 | Modified Oct 2022

Plague is a sudden and sometimes fatal bacterial disease caused by the bacteria Yersinia pestis. It is transmitted primarily by the fleas of rats and other rodents. This is the disease, often called the Black Death, that swept through Asia and then Europe in the 14th century. Over 25 million people (one third of the population there) died of this disease in Europe between 1347 and 1352. Devastating outbreaks of this disease recurred with regularity throughout the next 200 years.

Today, this disease can be controlled with antibiotics and other medications; however, it has not been eradicated. Small numbers of cases occur in wild animals in the western United States and throughout the world, including Eurasia, Africa, and North and South America. On average, 10 human plague cases are reported each year in the United States; the majority are from New Mexico, California, Colorado, and Arizona. Infection in dogs is extremely rare.

Yersinia pestis is maintained in the environment in a natural cycle between susceptible rodent species and their associated fleas. Commonly affected rodent species include ground squirrels and wood rats. Dogs are usually exposed to the bacteria by oral contact with secretions or tissues of an infected rodent or rabbit or by the bite of an infected flea. Potentially, the infected fleas can be transported into homes.

There are three forms of plague: bubonic, septicemic, and pneumonic. Bubonic plague causes swollen lymph nodes. Septicemic plague results when the plague spreads through the blood and affects multiple internal organs (such as the spleen, liver, heart, and lungs). Pneumonic plague refers to plague that causes affects the lungs (pneumonia); it develops from untreated septicemic plague or from infectious droplets spread by coughing from affected individuals.

Dogs are inherently resistant to the plague-causing bacteria. Dogs that do become infected with plague are less likely to show signs of illness than infected cats. Signs may include fever, lethargy, inflammation of the lymph nodes below the lower jaw, a pus-like lesion along the jaw, lesions in the mouth, and cough.

Due to the rapid progression of this disease, treatment for suspected plague (and infection control practices) should be started before a definitive diagnosis is obtained with bacterial cultures. Your veterinarian will recommend an antibiotic as standard treatment.

Along with treatment and diagnostic considerations, protection of people and other animals and initiation of public health interventions are critical when an animal is suspected to have plague. Even before a diagnosis is complete, animals with signs suggestive of plague should be placed in isolation and infection control measures implemented to protect you and your family, other household pets, and any other animals or individuals that have had contact with the infected pet.

To decrease the risk of pets and humans being exposed to plague, pet owners in areas where the disease may be found should keep their pets from roaming and hunting, limit their contact with rodent or rabbit carcasses, and use appropriate flea control. Your veterinarian can suggest the most appropriate flea control product for your pet.

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