What Is Bubonic Plague? China's Inner Mongolia Reports 'Black Death' Case

A case of bubonic plague has been confirmed in China's Inner Mongolia autonomous region, according to local health officials. The Bayannur city health commission said a herdsman was diagnosed with the disease on Sunday and is receiving treatment in hospital, with his condition reported as being stable, according to state media.

While it is not clear how the individual became infected, Bayannur city has put in place control measures as a precaution, issuing a level three alert that warns people not to eat, hunt or transport animals that can potentially harbor the disease in the region, such as marmots, Reuters reported.

The alert also encourages the public to report any dead or diseased rodents, as well as any suspected plague cases, with authorities saying the measures will stay in place for the rest of 2020.

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"At present, there is a risk of a human plague epidemic spreading in this city. The public should improve its self-protection awareness and ability, and report abnormal health conditions promptly," health authorities in Bayannur said.

Last week, authorities in the country of Mongolia—which neighbors the Chinese region of Inner Mongolia—reported two cases of bubonic plague associated with the consumption of marmot meat in Khovd Province.

What is bubonic plague?

Bubonic plague is a disease caused by the bacteria Yersinia pestis, usually found in small mammals and their fleas, that can be transmitted to humans.

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The most common route of transmission is when a flea infected with the bacteria bites a human, according to the U.S. Centers for Disease Control and Prevention (CDC.) However, people can also become infected via direct contact with infected tissues while handling an animal that is sick with plague or has died from the disease.

In the majority of cases, Yersinia pestis infections result in bubonic plague, however, the bacteria can also cause two other related diseases—septicemic plague and pneumonic plague. The latter is the only form that can be spread from person to person via the inhalation of respiratory droplets.

The Yersinia pestis bacteria was the cause of the Black Death—widely considered to be the deadliest pandemic in human history, which killed anywhere between 75 and 200 million people across Europe, Asia and North Africa in the 14th century.

The subsequent centuries saw several significant outbreaks of plague around the world. While cases of are rare today, outbreaks do still occur—although modern treatments have significantly reduced the mortality of the disease.

According to the World Health Organization, between 1,000 and 2,000 people are are affected by plague every year, with Madagascar, Peru and the Democratic Republic of Congo particularly badly affected.

Yersinia pestis, bubonic plague
A bubonic plague smear, prepared from a lymph removed from bubo of a plague patient, demonstrates the presence of the Yersinia pestis bacteria. Centers for Disease Control and Prevention/Getty Images

In China, outbreaks of plague are increasingly rare with only 26 cases resulting in 11 deaths recorded between 2009 and 2018. Plague is also present in the U.S. although cases are also very rare, mostly occurring in rural and semi-rural areas of the southwestern states. According to the U.S. CDC, an average of seven plague cases are reported annually in the country.

If left untreated, bubonic plague has a fatality rate of 30-60 percent, while pneumonic and septicemic plague almost always result in death, sometimes within 24 hours of the onset of symptoms in the case of the latter.

If patients are treated quickly with antibiotics and supportive therapy, the mortality rate for all forms of plague falls. For example, the mortality rate for bubonic plague drops to around 10 percent with treatment. However, this figure may be higher in some endemic areas, according to the WHO.

Symptoms of plague can appear between one and seven days after infection and they vary between the different forms.

With bubonic plague, patients develop fever, headache, chills and weakness, while the bacteria also causes lymph nodes in the body to swell up. These swollen, painful lymph nodes are referred to as "buboes." If the disease progresses, the buboes can turn into open sores filled with pus.

In May, 2019, a Mongolian couple died of plague after eating raw marmot kidneys, a local folk remedy believed to be beneficial for health.

Following the deaths of the couple—both residents of Mongolia's westernmost province Bayan-Ölgii—authorities declared a six-day quarantine in the region, during which no further cases were reported.

Mongolian health officials have warned people not to eat raw marmot meat because the animal can harbor the Yersinia pestis bacteria. Nevertheless, at least one person dies in the country annually of plague, often due to eating this meat, according to Mongolia's National Center for Zoonotic Disease.

This article was updated to include additional information about the deaths of a Mongolian couple from plague in May, 2019.

What Is Bubonic Plague? China's Inner Mongolia Reports 'Black Death' Case | Health