The couple had consumed the raw meat and kidney of a marmot, believed by some to be a folk remedy for good health, Ariuntuya Ochirpurev of the World Health Organization told the BBC.
The rodent is a known carrier of Yersinia pestis, the bacterium commonly associated with the highly contagious bubonic plague.
Following the couple's deaths on May 1, a quarantine was issued in Mongolia's western Bayan Olgii province, which borders China and Russia.
More than 100 people, including foreign tourists from Switzerland, Sweden, Kazakhstan and South Korea, had come into contact with the couple and were isolated and treated with antibiotics, according to Ochirpurev.
The quarantine was lifted Monday after no other cases were reported.
The Centers for Disease Control and Prevention says modern antibiotics are effective in treating plague, but without immediate care the infection can cause serious illness or even death. Patients typically develop fever, headache, chills, weakness and painful swelling in the lymph nodes.
"The Black Death," as it was known at the time, killed millions of people in the Middle Ages, but cases now are uncommon.
Human plague infections do continue to occur in the western United States, but significantly more cases occur in parts of Africa and Asia, according to the CDC.