Dozens of people were reported to be in isolation after a Russian laboratory worker at an institute dedicated to studying the plague and other infectious diseases died of an undisclosed illness.

The researcher, a 28-year-old female laboratory technician at the Irkutsk Research Anti-Plague Institute of Siberia, in the town of Shelekhov, died after being diagnosed with a pneumonia of “unknown” origin, according to Rospotrebnadzor, the Russian agency that handles infectious disease.