Staff at the US Centers for Disease Control and Prevention have been ordered to stop communicating with the World Health Organization, according to a new memo, dealing a significant blow to global health efforts.

In line with Trump's executive order to end all collaboration with the WHO, the CDC has been instructed to end all communications and work with the international public health agency.

Experts said the sudden stoppage was a surprise and would set back work on investigating and trying to stop outbreaks and brewing global threats.

A U.S. Centers for Disease Control and Prevention official, John Nkengasong, sent a memo to senior leaders at the agency on Sunday night telling them that all staff who work with the WHO must immediately stop their collaborations and “await further guidance.