MOSCOW: A laboratory worker at a plague research institute in Siberia has fallen ill and died in undisclosed circumstances, prompting authorities to quarantine dozens of people, and the head of Russia's health watchdog to fly to the Irkutsk region.

The death has sparked public health fears on social media, but the authorities said on Monday the situation was under control.

Plague is endemic to Siberia, location of the first known prehistoric human outbreak, as the bacterium that causes it, Yersinia pestis, is present among the small wild mammals in its vast wilderness and their fleas. It is rare for Russians to fall ill with plague, however, though cases in other parts of the world - notably Africa - occur every year.