Plague Outbreak of a Marmota himalayana Family Emerging from Hibernation

In April 2021, a plague outbreak was identified within one Marmota himalayana family shortly after emerging from hibernation, during plague surveillance in the M. himalayana plague foci of the Qinghai-Tibet Plateau. A total of five marmots were found dead of Yersinia pestis near the same burrow; one live marmot was positive of Y. pestis fraction 1 (F1) antibody. Comparative genome analysis shows that few single nucleotide polymorphisms were detected among the nine strains, indicating the same origin of the outbreak. The survived marmot shows a high titer of F1 antibody, higher than the mean titer of all marmots during the 2021 monitoring period (W = 391.00, Z = 2.81, p < 0.01). Marmots live with Y. pestis during hibernation when the pathogen is inhibited by hypothermia. But they wake up during or just after hibernation with body temperature rising to 37°C, when Y. pestis goes through optimal growth temperature, increases virulence, and causes death in marmots. A previous report has shown human plague cases caused by excavating marmots during winter; combined, this study shows the high risk of hibernation marmot carrying Y. pestis. This analysis provides new insights into the transmission of the highly virulent Y. pestis in M. himalayana plague foci and drives further effort upon plague control during hibernation.