GENEVA: The World Health Organization said on Saturday that it still does not know what caused the pneumonia that killed a Russian lab worker at an anti-plague research center in Siberia this month, and that no case of plague had been registered. The WHO said the Russian state regulator reported that tests of the lab worker and those who came in contact with her were negative for the high-threat pathogens tested, that her contacts still showed no symptoms, and that no further linked cases of
