Bubonic plague: Authorities in a city of China’s Inner Mongolia issued a warning on Sunday, a day after a hospital reported a case of suspected bubonic plague.

Sunday’s warning follows four reported cases of plague in people from Inner Mongolia last November, including two of the deadlier variant of plague—pneumonic plague.

The bubonic plague, known as the “Black Death” in the Middle Ages, is a highly infectious and often fatal disease that is spread mostly by rodents.

On July 1, state-run Xinhua news agency said that two suspected cases of bubonic plague reported in Khovd province in western Mongolia have been confirmed by lab test results. The confirmed cases are a 27-year-old resident and his 17-year-old brother. The brothers ate marmot meat, the health official said, warning people not to eat marmot meat.

What is the bubonic plague?

Bubonic plague is a rare but serious bacterial infection transmitted by fleas from rodents.

It is a zoonotic disease and it can be transmitted to other animals or humans. It mainly results from the bite of an infected flea. It may also result from exposure to the body fluids from a dead plague-infected animal.

It is one of the three plagues caused by bacterium Yersinia pestis. The other two being Septicaemic plague and Pneumonic plague.

It is spread by Yersinia pestis bacteria and requires urgent hospitalisation. According to the World Health Organisation (WHO), it can kill an adult in less than 24 hours, if not treated in time.

Without treatment, the plague can result in the death of 30% to 60% of the infected people.

What are the symptoms?

People infected with plague usually develop acute febrile disease with other non-specific systemic symptoms after an incubation period of one to seven days.

Symptoms typically include sudden onset of fever, chills, head and body aches, weakness, vomiting and nausea. Painful and inflamed lymph nodes can also appear during the bubonic plague.

Symptoms of the pneumonic form appear quickly after infection, sometimes less than 24 hours, and include severe respiratory symptoms such as shortness of breath and coughing, often with blood-tainted sputum.

How is plague treated?

Plague can be treated with antibiotics, and recovery is common if treatment starts early. In areas where there is a plague outbreak, people with symptoms should go to a health centre for evaluation and treatment.

Patients with pneumonic plague must be isolated and treated by trained medical staff wearing personal protective equipment.

When has it happened in the past?

Bubonic plague, known as the Black Death in the Middle Ages, killed tens of millions of people around the world in three major pandemics, with about a third of Europe’s population wiped out in the 1300s.

The bacterium is believed to have originated in Yunnan in southwest China. Opium trade routes from Yunnan caused the third global plague outbreak in 1894, but it has since become increasingly rare.

There were 3,248 cases worldwide, leading to 584 deaths—a fatality rate of 18%— between 2010 and 2015 according to WHO.

In the 14th century, bubonic plague resulted in Black Death in Asia, Europe, and Africa. It caused the death of over 50 million people — around 25% to 60% of the European population.