As she was dashing to catch a late evening connecting flight from New York to Washington DC on April 23 to participate in World Malaria Day, Margaret Chan noticed a missed call from one of her top aides whom she knew she should call back immediately.

Keiji Fukuda, an assistant director general at the Geneva headquarters of the World Health Organisation (WHO), had news of what could prove an even more lethal killer. He warned her that he was expecting test results on a new virus that was worrying public health specialists in North America.