Lab tests confirmed that two unidentified individuals had contracted the “marmot plague” in the region of Khovd, Mongolia’s National Center for Zoonotic Disease (NCZD) said in a statement.

The NCZD said it moved to quarantine the provincial capital and one of the region’s districts about 500 kilometers south of the southern Siberian republics of Tyva and Altai.

Vehicles are temporarily banned from entering the region, the state-run TASS news agency cited Mongolian media as saying.

The NCZD said it has analyzed samples taken from 146 people who it said had contacts with the two infected persons and identified 504 second-contact individuals. Media reports suggested that the victims were a 27-year-old male and a young woman of an unknown age.

Mongolia closed a key border crossing with Russia in May 2019 on suspicion that it may have played a role in an outbreak of the plague, stranding several Russian tourists. A husband and wife had died after eating marmot meat in that incident.

Experts say the direct descendants of the same bubonic plague that killed 50 million people in the 14th century still exist today, killing around 2,000 people a year.