“Everybody knows that pestilences have a way of recurring in the world; yet somehow we find it hard to believe in ones that crash down on our heads from a blue sky. There have been as many plagues as wars in history; yet always plagues and wars take people equally by surprise.” - Albert Camus, The Plague
“As Bubonic Plague Kills Another Man in Mongolia, Russia Starts Mass Vaccination Against Black Death”
- Aristos Georgiou (Newsweek, August 12, 2020)
It is hard to believe that things could have ever been worse (even far worse) than what we are now facing with the COVID-19 pandemic. But they were.
Plague was the cause of one of the most fatal pandemics recorded in human history (killing around 200 million people in Europe and Asia in the 1300s). And, panic was ignited recently by four reported cases of bubonic plague in Mongolia raising the question: “How worried should we now be about yet another pandemic arising in China?”
Plague redux. There are three different kinds of plague. The most common form is bubonic plague. The name of the disease derives from the ancient Greek word boubon, which refers to swelling in the groin by enlarged lymph glands, called buboes. This is one of the most evident symptoms of the illness; other common symptoms include fever, chills, diarrhea, and bleeding—typically from the mouth, nose, or rectum, or under the skin.
A second form, pneumonic plague, is a highly lethal infection of the lungs that can be spread by coughing. The third form, septicemic plague, occurs when the plague bacterium invades the bloodstream, and is an almost certain death sentence. People dying of septicemic plague turn a very dark color—hence the name Black Death.
Unlike COVID-19, plague is a bacterial infection, not a viral one. The etiologic agent Yersinia pestis, was discovered in 1894 by Alexandre Yersin, a student of Louis Pasteur and Robert Koch. Yersin also found the bacterium in rats.
Plague is zoonotic, an infection transmitted from animals to humans. Rats are the most common carriers although we now know that many different rodents, from mice to prairie dogs, also carry the disease. But bubonic plague is not spread directly from rats to humans. Fleas serve as intermediaries. First the rat gets infected; then a flea living on the rat bites the rat and gets infected as well; then the flea jumps from the rat to a human and bites them, thus transmitting the infection. Bubonic plague is fatal in 50% to 60% of all cases.
A recent study of bones from humans who died in the Bronze Age, some 5,000 years ago, detected the DNA of Y. pestis. For centuries, travel along trade routes to and from China—and from port to port on ships carrying both humans and flea-laden rats—was the genesis of many plague epidemics. There have been 28 epidemics of bubonic plague in recorded history, including the Great Plague of Athens (430-427 BCE); the Plague of Justinian (541-542), which killed 25-50 million people in the Eastern Roman Empire; the Black Death (1346-53), which wiped out 30% to 60% of all humans in Europe; and the Great Plague of London (1665), which killed 100,000 Londoners—20% percent of the city’s population—in seven months.
Plague in the United States. Bubonic plague first came to the western United States about a century ago. Y. pestis became established in wild rodent populations, including prairie dogs. As a result, a handful of cases of bubonic plague are reported annually in the U.S., all in the west. Because of the introduction of antibiotics, however, the death rate in the United States from plague fell from over 66% early in the 20th century to 11% a century later.
In the last few decades, seven human plague cases on average per year have been reported in the U.S. Recently, California reported its first plague case in five years. This happened in the South Lake Tahoe area where a man was diagnosed with plague following a walk along a trail with his dog. It is thought that the flea causing the infection came from the dog. This incident has led the California Department of Public Health to issue a warning that in addition to wild rodents, dogs and cats may also carry plague-infected fleas.
While plague can be successfully treated with antibiotics, a U.S. Food and Drug Administration-approved vaccine to prevent plague is not available. Therefore, visitors to national parks in the western United States should protect themselves by spraying with insect repellant containing DEET, and should avoid feeding squirrels, chipmunks, and other rodents.
New plague outbreak in Mongolia. News of the plague first broke out on July 5, 2020 when a herdsman from the city of Bayannur in the Chinese region of Inner Mongolia was diagnosed with bubonic plague. Since then a total of four cases have been confirmed with two deaths including a 15-year-old boy in a remote southwest province of Gobi-Altal, who became ill after eating the meat of a marmot. All four cases have been linked to eating or coming in contact with marmots—a large member of the squirrel family. While it is illegal to hunt marmots in Mongolia, this rodent is considered a delicacy, and its meat is believed to provide health benefits.
Of the 21 Mongolian provinces, 17 are now considered at risk of bubonic plague. A number of people with contact with the known cases are quarantined, and in nearby regions of Russia warnings have been issued to residents not to hunt or eat marmots. In the Republic of Tuva, which borders Mongolia, a mass vaccination campaign to prevent the spread of plague has begun. (There is no evidence, however, that Russia’s plague vaccine is safe or effective.)
How worried should you be? Unless you are planning a trip to Mongolia, which isn’t recommended (or perhaps even possible) given the dangers of and restrictions related to travel in light of COVID-19, the answer is not to worry. Even if you are going to or are currently in Mongolia, you have almost nothing to fear (assuming you can stay clear of marmots and the marmot flea, Oropsylla silantiewi).
If you are like many in the U.S. who are road-tripping this summer to escape the confines of home, and if you plan to go to places with wild rodents of any kind, keep in mind that you should keep your distance. Chipmunks, squirrels and prairie dogs may be “cute” and seem harmless but they are not. The fleas that they harbor can carry the deadly plague bacterium.
Perhaps the moral to this story is that we need to treat wildlife with greater respect. Zoonotic infections are common; some of you may recall my earlier Germ Gems posts about the connection between COVID-19 and animals (such as bats, civets, pangolins and others). Another parallel with COVID-19 is the need for an effective plague vaccine (the efficacy and safety of the Russian plague vaccine, as is the case with the recently released Russian vaccine against SARS-CoV-2, is suspect at best).
But for me the most important lesson from the history of plague, which also applies to COVID-19, is humility. Just as many pandemics have emerged unpredictably, some have submerged or even disappeared without our understanding exactly why. In the case of plague, which has almost crushed humanity on many occasions, why has it become a relatively minor challenge in most countries in modern times? It’s not because the carriers, rats and other rodents, have disappeared. And, as mentioned, we can’t credit its control to an effective vaccine. What is it then? I certainly don’t know, but I hope COVID-19 would adopt a similar disappearance act sometime soon!
