NEW YORK — U.S. public health officials have been told to stop working with the World Health Organization, effective immediately.

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 agency staff who work with the WHO must immediately stop their collaborations and “await further guidance.”

Experts said the sudden stoppage was a surprise and would set back work on investigating and trying to stop outbreaks of Marburg virus and mpox in Africa, as well as brewing threats from around the world. It also comes as health authorities around the world are monitoring bird flu outbreaks among U.S. livestock.

The Associated Press viewed a copy of Nkengasong’s memo, which said the stop-work policy applied to “all CDC staff engaging with WHO through technical working groups, coordinating centers, advisory boards, cooperative agreements or other means — in person or virtual.” It also says CDC staff are not allowed to visit WHO offices.