The same disease that wiped out a third of Europe in the 14th century — plague — has sickened at least two people this month in Inner Mongolia, an autonomous region of northern China.
Globally, there are between 1,000 and 2,000 reported cases of plague each year, according to the World Health Organization, and many of them occur in the Democratic Republic of Congo, Madagascar, and Peru. But the case that’s being handled out of Beijing’s Chaoyang Hospital is particularly concerning because it relates to a middle-aged married couple afflicted with a virulent version of the infection called pneumonic plague, according to the New York Times.
While plague was once referred to as “the black death” and certainly has its share of creepy symptoms, many of those infected with the most common, modern bubonic plague variety survive with proper, prompt treatment. The Chinese government has assured the public that it has properly quarantined the individuals and that risk for transmission appears low, according to the Times.
Still, people on Chinese social media are expressing concern that the patient count is secretly higher than reported or that people have already died, according to UPI. There’s no evidence to back up those claims, but the government isn’t traditionally transparent with its citizens about disease outbreaks. And the last few outbreaks — 12 cases in 2009 with three deaths; 7 cases in 2010 with two deaths; three cases in 2014 with three deaths — have instilled fear that more people will die. Pneumonic plague is nearly always fatal if not properly treated.
There is no effective vaccine to prevent the infection.
Plague is most often contracted after a person is bitten by an infected rat or flea, but, depending on the variety, it can also spread through contact with infected animals or humans. There are three variants of plague, and the most common, bubonic plague, has a mortality rate of 1 to 15 percent if treated immediately, although it’s hard to determine the proper death rate because cases in the developing world aren’t often reliably diagnosed.
The second most common variety, septicemic plague, can develop if bubonic plague is left untreated. Notably, two Mongolians were also sickened with the plague in May after they ate the raw kidney of a marmot, a large squirrel found in the region that’s believed to bring someone good health if they eat its uncooked innards. That couple died of septicemic plague.
The least common plague — pneumonic, which the two patients from Inner Mongolia are experiencing — is also the most deadly. That infection, which can result from untreated plague that’s spread to the lungs, can spread through airborne droplets.
Most commonly, a person infected with plague will develop intensely painful, red “buboes” around the site of their infection— really just swollen lymph nodes doing their job of trying to rid the body of the bacteria responsible for the illness. The buboes are followed by a high fever, chills, and extreme weakness. The plague becomes far more serious if it circulates to the bloodstream or the lungs. That’s when a doctor might see one of plague’s most gruesome symptoms: blackening, dead skin.
The United States reports about 7 human plague cases each year — often the bubonic form, and often in the western half of the country, according to the U.S. Centers for Disease Control and Prevention.
This article originally appeared on VICE US.