Explained: A Russian report says a worker at a Siberian plague institute fell ill and died of an unknown cause

A staffer at the Irkutsk Anti-Plague Research Institute contracted pneumonia of an unknown cause

pneumonic plague

A less common but severe form of plague that can spread from person to person, according to the WHO

Yersinia pestis

The bacterium that causes plague, usually found in small mammals and their fleas

Rospotrebnadzor

Russia's public health watchdog agency

etiology

The cause or origin of a disease

quarantine

Restricting movement or access to prevent the spread of disease, as imposed on the hospital