(CNN) A local folk remedy thought to provide good health had the opposite effect for one Mongolian couple: After eating the raw kidney of a marmot, the pair died of bubonic plague, AFP news agency reported on Monday. Health authorities responded by declaring a quarantine that included locals and foreign tourists who had come into contact with the couple.

Plague, one of the deadliest bacterial infections in human history, caused an estimated 50 million deaths in Europe during the Middle Ages. Symptoms, which usually appear within one to seven days after infection, include painful, swollen lymph nodes, called bubos, as well as fever, chills and coughing.

"After the quarantine [was announced] not many people, even locals, were in the streets for fear of catching the disease," Sebastian Pique, a US Peace Corps volunteer living in the region, told AFP.

Plague has made a recent comeback. Having caused close to 50,000 human cases during the last two decades, it is now categorized by World Health Organization as a re-emerging disease. Worse, the bacterium causing plague, if converted into an aerosolized form, is considered one of the most likely biothreats and is classified as such by the US Centers for Disease Control and Prevention.

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