On Thursday, the Chinese authorities lifted the 9-day quarantine they had imposed in a part of Yumen City in northwest Gansu Province after a resident had died of plague on 16 July.

The authorities had effectively sealed off the old downtown area of the northwestern city, stopping 30,000 residents leaving the area. They also quarantined 151 people who had been in direct contact with the 38-year-old man who died, and who is thought to have caught the disease from a dead marmot, a member of the squirrel family.

The state broadcaster China Central Television says the man lived in a township called Chijin, which had also been sealed off.

Chinese state media report that during the quarantine, disease prevention and control specialists from the National Health and Family Planning Commission, together with local authorities, carried out disinfection and rat extermination, and ran education sessions to raise awareness of how people can guard against infection.

According to Chinese experts, the plague is present in an “active,” communicable phase in the local rat population.

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According to Chinese experts, the plague is present in an “active,” communicable phase in the local rat population.

No further cases of the disease had been reported by Tuesday, according to Xinhua news agency, which notes that in China, plague is categorized as a “Class A infectious disease, the most serious under China’s Law on the Prevention and Treatment of Infectious Diseases.”

Plague is a disease caused by the bacterium Yersinia pestis that affects humans and other mammals and is probably most well-known for wiping out a significant proportion of the population of Europe in the Middle Ages.

Humans usually contract the disease after coming into contact with an animal infected with plague, or after being bitten by a rodent flea that is carrying the bacterium.

Unless it is treated promptly with antibiotics, the disease causes serious illness or death within 24 hours.

According to the US Centers for Disease Control and Prevention, cases of human plague continue to occur in the western United States, but in terms of global numbers, the vast majority occur in Africa and Asia.

The South China Morning Post reports that the recent Chinese victim is thought to have come into contact with an infected, dead marmot that he chopped up to feed to his dog – he went on to develop a fever later that day.

Infection by Y. pestis bacteria causes three types of plague:

  • Bubonic – where bacteria infect the lymph system, usually as a result of a bite from an infected flea or rodent
  • Septicemic – where bacteria enter the bloodstream. As in bubonic, this mostly happens as a result of a bite from an infected flea or rodent, but it can also occur from untreated bubonic or pneumonic plague
  • Pneumonic – this is the most serious form, where the bacteria infect the lungs and cause pneumonia.

The Chinese man who died is thought to have contracted the pneumonic form.

Pneumonic plague is also contagious – if someone has pneumonic plague and coughs, droplets containing plague bacteria are released into the air and infect other people who breathe them in.

China has seen few outbreaks of plague in recent years. Most happen in remote rural areas in the west of the country. State media say there were 12 cases and three deaths in the province of Qinghai in 2009, and one in Sichuan in 2012.

In 2008, Medical News Today reported how scientists suggested the reason plague is so lethal is because of a single genetic mutation.