“After a while, the fashion of the contagion began to change into black or livid blotches, which showed themselves in many [first] on the arms and about the thighs and [after spread to] every other part of the person, … a very certain token of coming death.”
The Decameron, Giovanni Boccaccio,14th-century Italian poet
“While extremely rare, the disease is still around today, with a man in New Mexico dying of plague in March after being hospitalized for the disease and a person in Oregon being diagnosed with bubonic plague in February after likely being infected by their pet cat.”
Susan Scutti and Katie Hunt, CNN Health and Medical, July 5, 2024
Bubonic plague is on the screen again. For the general public, it is on the television screen—a fictional tale about the disease is airing on a popular streaming service. For those of us in infectious diseases, it is on our radar screen; the Centers for Disease Control and Prevention (CDC) reported that as of July 24, 2024, there were three cases of plague in the U.S. As it’s been almost four years since my Germ Gems post on plague (See “What Happens in Mongolia Stays in Mongolia (or does it?),” August 19, 2020), it seemed like a good time to revisit the disease that caused the “deadliest pandemic in human history.”
Plague: a recap. Plague is a bacterial infection caused by the bacillus Yersinia pestis. (It is named for Alexandre Yersin who discovered the bacillus in 1894.) It is zoonotic—an infection transmitted from animals to humans. Rats are the most common carriers of the disease. But many other rodents and, in some cases, even rabbits or domestic animals (dogs and cats) can carry the disease. The “carrier” does not, however, spread the disease directly to humans.
In 1898, the French physician Jean-Paul Simond determined that the disease was a vector-borne infection, i.e., transmitted from rodents to humans via flea bites. (Recent studies suggest that human body lice can also harbor Y. pestis.) First the rat (or other animal) gets infected and is bitten by a flea living on the rat thereby infecting the flea. The flea then jumps from the rat to a human, bites the human and transmits the infection. While the bacterium is the culprit, the flea—the intermediary— is the real offender.
There are three different forms of plague: bubonic; pneumonic; and septicemic. Bubonic plague is the most common. Its name is derived from the Greek word boubon, referring to enlarged lymph glands called buboes. This is one of the most evident symptoms of the disease. Other common symptoms include fever, chills, diarrhea and bleeding—typically from the mouth, nose, or rectum or under the skin. Bubonic plague is fatal in 50% to 60% of cases.
Pneumonic plague is a highly lethal infection of the lungs (pneumonia) that can be spread by coughing. It is almost always fatal.
Septicemic plague is also almost always fatal. It occurs when the plague bacterium invades the bloodstream. This causes an associated darkening of the skin—hence the name Black Death.
Plague in perspective. According to Wikipedia’s “List of epidemics and pandemics,” in human history, nineteen pandemics have been responsible for at least 1 million deaths, and of these, six were due to bubonic plague. The Black Death in the 14th century was one of the worst; it claimed the lives of 30-60% of the European population—a contested death toll of 25-50 million people. (Some experts think this is an overestimate and are still debating how many people actually were killed by Y. pestis in this medieval pandemic.)
Somewhat surprisingly, plague wasn’t among the infectious diseases that the explorers brought with them to the New World—diseases that killed close to 90% of all indigenous peoples. (See July 10, 2024 Germ Gems post, “The Columbian Exchange: Microbes That Conquered the Americas.”) Instead, plague was introduced into the U.S. in 1900 by rat-infested steamships that had sailed from affected areas, mostly from Asia. Plague epidemics then occurred in port cities. The last urban plague in the U.S. occurred in Los Angeles from 1924 through 1925.
Now, an average of seven cases of plague are reported each year to the CDC and the World Health Organization reports 1,000 to 3,000 cases worldwide every year. The U.S. Food and Drug Administration has not approved a vaccine for plague, but the disease can be treated successfully with antibiotics such as levofloxacin.
Plague is no longer the scourge that it was in the Middle Ages. And while it is down, it is not out. The bacterium, carriers, and vector are all still here. Given the right conditions, could plague rear its head yet again and cause another horrendous pandemic? I don’t know the answer, but I offer these words of cautious: never say “never.”
Excellent, well written