It seems strange to be writing about plague in the year 2000, a disease that has decimated the world’s human population on a regular basis. There are no statistics on the number of animals killed by the plague. A global plague epidemic killed an estimated 100 million people in 542, including one-quarter of Europe’s population. Another epidemic, dubbed the “Black Death,” started in 1346 and lasted 300 years, killing 25 million people. A third epidemic is still going on in the twenty-first century. Between 1965 and 1970, more than 25,000 cases of plague were reported in South Vietnam; the true figure could be as high as 250,000.
“A curse on both of your residences…”
Human and animal health have been and will continue to be threatened by the plague. Plague, caused by the bacteria Yersinia pestis, persists in semiarid rodent populations all over the world. Between 1944 and 1995, more than half of the 383 confirmed cases of human plague in the United States occurred in New Mexico, with the majority of the rest occurring in Arizona, California, and Colorado. The disease was most commonly transmitted to humans via flea bite.
Mortality today ranges from 5% to 20% with appropriate antibiotic therapy. The Yersinia organism then multiplies in the flea’s stomach and is passed on to the next animal bit by the flea. Prairie dogs, rock squirrels, and ground squirrels are the most common infected wild hosts in the United States, with dogs and cats capable of transmitting the flea from wildlife to humans.
Aside from flea bites, cats can become infected with the plague by eating infected rodents, and humans can become infected by handling infected rodents brought home by their dog or cat. Depending on the type of plague, pets, particularly cats, may transmit Yersinia pestis through bites and scratches or sneezing and coughing (see below). In 1977, the first report of a domestic cat transmitting plague was published, and veterinarians and their assistants have been responsible for a large proportion of confirmed cases of plague. It’s unclear why cats are more vulnerable to plague than other carnivores that eat rodents.
Three faces of plague of cat
There are three types of plague: bubonic, pneumonic, and septicemic. Many cats had lymph node abscesses beneath the jaw. Infection occurs when bones from the carcass scrape or pierce the oral cavity or throat. Bubonic plague occurs when the organism is contained at the lymph nodes of the mouth and throat.
If the organism manages to get past the lymph node barrier and into the bloodstream, it may be filtered by and confined to the lungs, resulting in pneumonic plague. If the organism, on the other hand, outnumbers the cat’s defense mechanisms, a devastating blood infection occurs, resulting in septicemic plague. This type of disease frequently impairs the ability of the blood to clot. As there is widespread hemorrhage and bleeding, tissues turn a reddish black color, hence the name “Black Death.”
An examination of 119 documented feline plague cases revealed that 53% were bubonic, 10% were pneumonic, 8% were septicemic, and 29% were unclassified (but presumed to be septicemic) (but presumed to be septicemic). There is no one age, breed, or sex of cat that is more vulnerable than others. Nonspecific symptoms such as lethargy, fever, and loss of appetite were common. A typical scenario might look like this: A plague-infected rodent is eaten by a cat. The overall mortality rate in this study was 33%, with the pneumonic form having the highest risk of death.
A flea will typically bite and consume the blood of a plague-infected animal. Tetracyclines appear to be the most effective antibiotics in simple cases. So far, the organism has not developed antibiotic resistance. However, the efficacy of antibiotic therapy for both humans and animals is dependent on timing. Antibiotics are of little benefit if administered more than 24 hours after the onset of the pneumonic or septicemic forms of the disease, and the prognosis becomes dire.
Cat owners in plague-endemic areas should keep their cats from hunting and remove outdoor rodent-infested areas such as piles of wood or brush. Meticulous flea control with the new once-a-month topical insecticides will reduce the risk of fleas carrying plague into the home. Even better, keep cats indoors. With caution, diligence, and luck, the twenty-first century will avoid losing millions of its citizens, as well as their animal companions, to this ancient fate.
Dr. Plotnick was former vice president of ASPCA Bergh Memorial Animal Hospital.
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