The World Health Organisation (WHO) has put scientists and health workers around the globe on alert for a new and potentially deadly pathogen – Disease X.

Each year the Geneva-based organisation, which is charged with monitoring and safeguarding world health, convenes a high-level meeting of senior scientists to list diseases that pose a serious risk of sparking a major international public health emergency.

In previous years the list has been confined to known killers such as Lassa fever, which is currently sweeping Nigeria, and Ebola, which killed more than 11,000 people in an epidemic in West Africa between 2013 and 2016.

However, this year a ninth mystery pathogen has been added to the watch list for the first time. "These diseases pose major public health risks, and further research and development is needed, including surveillance and diagnostics", said the WHO in a statement.