Roughly 200 people are under medical observation, several hospitals are under quarantine, and dozens are in isolation in Russia following the unexplained death of an infectious disease researcher at the Irkutsk Anti-Plague Research Institute of Siberia, in the town of Shelekhov, according to early reports of the situation on Sunday and Monday.

Researcher Darya Shipilova reportedly died last week from pneumonia of “unknown” cause, according to Rospotrebnadzor, a Russian public health agency.