Plague is a sudden and sometimes fatal bacterial disease caused by 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) 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.
Yersinia pestis is maintained in the environment in a natural cycle between susceptible rodent species and their associated fleas. Commonly affected species include ground squirrels, prairie dogs, rabbits, and wood rats. Cats are usually exposed to the bacteria by oral contact with secretions or tissue of an infected rodent or rabbit (for example, eating an infected animal) or by the bite an infected flea. Cats that roam or hunt in areas where the bacteria is present have an increased risk of developing plague. Potentially, infected fleas can be transported into homes.
In mammalian hosts, plague occurs in one of 3 forms: bubonic, septicemic, or pneumonic. Bubonic plague causes swollen lymph nodes. The bacteria enter the body via the skin (by a flea bite) or the mucous membranes (by ingestion of infected animal tissue). The bacteria then travel via the lymphatic vessels to regional lymph nodes. These infected lymph nodes are called buboes, the typical lesion of bubonic plague. Septicemic plague can develop when the organism spreads through the bloodstream and affects numerous organs, including the spleen, liver, heart, and lungs. Pneumonic plague affects the lungs. It can develop from inadequately treated septicemic plague or from infectious respiratory droplets, such as those from a coughing pneumonic plague patient.
The most common presentation of plague in cats is bubonic plague. Cats with bubonic plague usually have fever, loss of appetite, lethargy, and an enlarged lymph node that may be abscessed and draining. Ulcers in the mouth, skin abscesses (pockets of pus and infection), discharge from the eyes, diarrhea, vomiting, and diffuse spreading inflammation of tissues beneath the skin have also been documented. High fever may be present. Cats with primary septicemic plague have no obvious disease of the lymph nodes but have fever, lethargy, and poor appetite. Septic signs may also include diarrhea, vomiting, excessively rapid heart rate, weak pulse, and breathing distress. Primary pneumonic plague has not been documented in cats. Cats with secondary pneumonic plague may have all the signs of septicemic plague along with a cough and other abnormal lung sounds.
To diagnose plague, your veterinarian will take samples (such as blood, fluid from the lymph nodes, or a swab from the mouth or throat) for testing and confirmation of the presence of plague-causing bacteria. Blood tests may also help.
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. Your veterinarian will recommend an antibiotic as standard treatment.
The duration of infectivity in treated cats is not known with certainty, but cats are thought to be noninfectious after 72 hours of appropriate antibiotic treatment if there are indications of improvement. During the infectious period, cats should remain hospitalized, especially if there are signs of pneumonia. Human cases have occurred in cat owners trying to give medications by mouth at home, exposing them to contact with the mouth and associated infectious secretions.
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 that suggest plague should be placed in isolation at a veterinary hospital, and infection control measures should be implemented for the protection of you and your family, other household pets, and any other animals or individuals that have had contact with the infected animal. Examples of infection control measures include disinfection, protective clothing (such as gloves and face masks), and possibly preventive antibiotics for in-contact animals or people. Your veterinarian will contact local public health officials so they can help minimize spread of the disease.
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 cat.