At the beginning of September, the U.S. Forest Service posted a notice in the Lake Tahoe area of California warning the public that chipmunks, ground squirrels, and other wild rodents in the area had been found to be infected with plague. In August, a local Tahoe resident had fallen ill with the disease after walking his dog along the Truckee River. In the spring of this year, a 20-year-old man in Arriba County, New Mexico, died from the flea-borne illness. Outside the United States, the Associated Press reported that the Congo has seen an upsurge in infections this year, with 10 deaths recorded as of September 2. In China, the plague had swept through at least 17 provinces by the end of August, and two people died from the disease in Mongolia. Here are 10 important things you should know about the plague. “Plague is actually not something you hear about very often, but if you do get a few cases it tends to be widely reported because of the notorious outbreak in the Middle Ages,” says William Schaffner, MD, a professor of preventive medicine in the department of health policy at the Vanderbilt University School of Medicine in Nashville, Tennessee. “Public health officials are not very concerned, because the United States typically sees between one and six plague cases each year and they’re localized to places where people usually get close to prairie dogs [and other ground-welling rodents].” Because the disease is rarely known to be passed from human to human, Dr. Schaffner notes that it is highly unlikely to be as widespread as flu or COVID-19.
2. Where Does Plague Come From?
The bacteria that cause plague (Yersinia pestis) transmit to humans through fleas that breed among certain ground-dwelling rats, rock squirrels, wood rats, ground squirrels, prairie dogs, chipmunks, mice, voles, and rabbits. During the infamous plague of the 1300s, the pestilence was attributed to black rats, also known as roof or house rats. So, why don’t we see plague today wiping out urban areas, which are notorious breeding grounds for rats? City rodents are the wrong type of rat, according to the plague expert Michael Antolin, PhD, a professor in the department of biology at Colorado State University in Fort Collins. “Rattus rattus, the black rat, has fleas that are very good at biting humans, and the Norwegian rat [found in cities like New York] has a flea that just has no care for us whatsoever,” says Antolin. “Plus, the black rat will live with humans, while the Norwegian rat will not — it lives in the sewers.”
3. How at Risk Am I of Getting the Plague?
Your chance of getting plague depends on where you live. The Centers for Disease Control and Prevention (CDC) cautions residents in rural and semirural areas of the western states where plague occurs to be on the alert for public health warnings of an outbreak in their area, like the one recently issued in Lake Tahoe. If they are walking outside near where infected animals live, they may get bit by a disease-carrying flea.
4. Can a Pet Give Me the Plague?
If you are the owner of a pet that goes outdoors, your risk may increase. “Humans certainly get plague from fleas on dogs,” says Antolin. “Your dog is running around and checking things out. Flea jumps on dog. Flea goes home with dog. Flea gets on human. That’s a fairly common exposure.” Cats, many of which like to hunt rodents, are also known plague transmitters. Antolin adds that hunters may want to be extra careful as well. “If a hunter shoots an infected rabbit and skins it, that’s a good way to get plague,” he says.
5. Are There Other Risk Factors to Be Aware Of?
Antolin suggests that residents in rural areas of the western United States keep their eye on the weather. “In relatively wetter years, there’s more plague — that’s a pattern that’s seen worldwide,” he says. “That may be why we have some more plague cases this year.” The CDC highlights 1983 as a particularly big year for plague in the United States, when 16 human cases were reported between April 21 and June 17. “That was the last really big El Niño year in the West,” says Antolin. “New Mexico can get monsoon rains in the summer, and that’s when their cases may go up.” Based on a study at Colorado State, Antolin speculates that plague bacteria may survive dormant in amoebas in the soil, and then possibly be released in rainier periods.
6. What Are the Symptoms of Plague?
Plague bacteria can cause fever, headache, weakness, chills, and other bodily distress, depending on which form a person gets (bubonic, septicemic, or pneumonic). The CDC details possible symptoms. With bubonic plague, germs multiply in the lymph nodes (usually near the groin) and cause a swelling called a bubo. With septicemic plague (which can develop from untreated bubonic plague), bacteria enters the bloodstream and may cause skin and other tissues to turn black and die. With pneumonic plague, Bacillus bacteria enter the lungs, causing patients to develop shortness of breath, chest pain, cough, and sometimes bloody or watery mucus.
7. How Deadly Is the Plague?
The British independent health journal Bandolier estimates that the chance of contracting plague is about 1 in 3 million, and the odds of dying from it are about 1 in 30 million. Numbers from the CDC show that antibiotics have reduced mortality rates to about 11 percent from about 66 percent during the pre-antibiotic era (1900 through 1941). If left untreated, the illness can be deadly, so it’s important to have symptoms diagnosed and get treatment. Commonly available antibiotics can stop the plague if they’re taken early, before the disease progresses.
8. Is Plague Easily Diagnosed?
Because plague is seldom seen and the symptoms can be similar to flu and other illnesses, medical professionals may not quickly identify plague as such — and that can lead to lethal outcomes. “The problem is that plague is rare, and the symptoms are often not immediately recognized, unless you’re a doctor in a local area that’s on the alert,” says Schaffner. That was the unfortunate case for Taylor Gaes, a star athlete in Fort Collins, Colorado, who died the day after his 16th birthday in 2015. Gaes had been sick with aches and other symptoms that made his parents think he had the flu. When he started coughing up blood, they rushed him to a hospital, where he stopped breathing and died. It was only after the fact that doctors discovered that the football quarterback and baseball starting pitcher had been infected with the plague.
9. What Can People Do to Prevent Getting the Plague?
The CDC provides a list of tips to avoid getting the plague in the first place. These include reducing potential rodent habitats in areas where you live or work, wearing gloves if you are handling or skinning potentially infected animals, wearing insect repellents in areas where you might be exposed to infected fleas, using flea-control products on pets, and not allowing pets to roam freely in areas that have been flagged for having rodent populations that may be infected. A plague vaccine is not available. New plague vaccines are in development but are not expected to be commercially available in the immediate future.
10. Where Can I Stay Up-to-Date Regarding Plague?
The World Health Organization provides detailed data on plague around the world, and the CDC keeps tabs on the disease in the United States, including maps and charts showing hot spots for infections and death tallies from year to year. “We don’t expect an outbreak, but it is still an organism whose name evokes attention, if not anxiety, so we keep our eye on it,” says Schaffner.
