Marmots are large ground squirrels, a type of rodent, that have historically been linked to plague outbreaks in the region.
Tests confirmed the teenager had contracted bubonic plague and authorities imposed quarantine measures in the Tugrug district of Gobi-Altai province.
The quarantine, which began on Sunday, will run until Saturday, and authorities have already isolated 15 people who came into contact with the teenager. All of them are healthy.
Rodents are the main vector of plague transmission from animals to humans, but the disease can also be passed on through flea bites or from person to person.
Plague killed an estimated 50 million people in Europe during the Black Death pandemic in the Middle Ages, but modern antibiotics can prevent complications and death if administered quickly enough.
Bubonic plague, which is one of plague’s three forms, causes painful, swollen lymph nodes, as well as fever, chills and coughing.
Mongolia has recorded 692 cases of marmot plague from 1928 to 2018. Of those, 513 died of the disease, equivalent to a mortality rate of just over 74%.
Earlier this month, two other people tested positive for bubonic plague in the neighboring province of Khovd, prompting warnings from officials in nearby Russia.
Officials from Russia’s Ministry of Agriculture and Food told citizens in the border area not to hunt marmots or eat marmot meat, and to take preventive measures against insect bites.
The Russian Embassy in Mongolia cited Sergei Diorditsu, a World Health Organization (WHO) representative in Mongolia, who reportedly said the province sees seasonal outbreaks of the plague, according to Russian state media outlet RIA Novosti.
“There are natural foci of plague in Mongolia and the disease is spread by tarbagans (Mongolian marmots),” the embassy said.
“The problem is that local residents who, despite all prohibitions and recommendations of local authorities, continue to hunt them and eat them, as this is a local delicacy.”
Authorities in the Chinese region of Inner Mongolia also confirmed a case of the plague in the city of Bayannur, northwest of Beijing, on July 7, according to the state-run Xinhua news agency.
In 2019, a couple in Mongolia died after eating a raw marmot kidney, triggering a quarantine that left several tourists stranded in the region.
Last week, a squirrel in the US state of Colorado tested positive for the plague.
The US reports up to a few dozen cases every year, according to the Centers for Disease Control. Two people died in Colorado from the plague in 2015.
The plague has recently made a comeback, and the World Health Organization has categorized it as a re-emerging disease.
Anywhere from 1,000 to 2,000 people get the plague every year, according to the WHO, but that estimate does not account for unreported cases.