A woman suffers the black death after eating an infected rodent delicacy.
The 25-year-old is being held in isolation with 19 people she has had contact with in Khovd Province, Mongolia.
Another unrelated case in Khentii province is also under investigation, reports say.
Separately, there are fears in China that a three-year-old boy in southwestern Yunnan Province has contracted a plague, also known as the Black Death.
The Chinese incident came after three dead rats were found in a village in Menghai County.
The county has launched a Stage IV Emergency Response to prevent the disease from spreading, the Global Times reported.
Bubonic plague is a bacterial disease transmitted by fleas that live on wild rodents and can kill an adult in less than 24 hours if not treated in a timely manner.
The infection of the woman in Altai-Soum or the Khovd province of Mongolia has been confirmed by laboratory test results, reported the country’s National Center for Zoonotic Diseases (NCZD).
She ate marmot meat last week, the center said.
Tests are reportedly ongoing on a suspected victim in Khentii province.
Groundhog hunting is illegal in Mongolia, but many consider the rodent a delicacy and ignore the law.
This year Mongolia reported 22 suspected cases, six of which have been confirmed, the highest number in a decade.
Three of the six died, most recently a 38-year-old man in Khovsgol province who ate an infected marmot earlier this month.
The previous two deaths this year were a 15-year-old boy in Govi-Altai Province in July and a 42-year-old man in Khovd Province in August.
17 of the 21 Mongolian provinces are now threatened by the bubonic plague, warned the NCZD.
People were warned not to hunt, eat, sell, buy, or transport marmots.
Two deaths were also reported in China’s Inner Mongolia that year.
Russia has taken important steps to stop the Black Death from spreading across its borders with Mongolia and China as the region also battles Covid-19.
Tens of thousands of people have been vaccinated in border areas in the Siberian republics of Tuva and Altai.
An eruption was recorded on the Ukok Plateau of the Altai Mountains in Russia – for the first time in more than 60 years.
Up to 200 million people were killed in the 14th century by the Black Death – the bubonic plague.