WASHINGTON — The Food and Drug Administration wants all U.S. blood centers to start screening for Zika, a major expansion intended to protect the nation’s blood supply from the mosquito-borne virus.

Friday’s advisory means all U.S. states and territories will need to begin testing blood donations for Zika. Previously, the FDA had limited the requirement to Puerto Rico and two Florida counties.

“There is still much uncertainty regarding the nature and extent of Zika virus transmission,” said Dr. Peter Marks, director of the FDA’s biologic products center, in an agency release. “At this time, the recommendation for testing the entire blood supply will help ensure that safe blood is available for all individuals who might need transfusion.”

Blood collection sites already test donations for HIV, hepatitis, West Nile virus and other blood-borne viruses.

FDA officials said Zika testing is already under way in Puerto Rico and parts of Florida, where “it has shown to be beneficial in identifying donations infected with Zika virus.”

The FDA has authorized use of two experimental blood-screening tests for Zika, one made by Roche and another from Hologic. Several testing sites are already voluntarily using the technology, including blood centers in Texas. The cost of adding Zika testing to the blood screening process is less than $10, according to officials at South Texas Blood and Tissue Center.

Since February, U.S. blood centers have been turning away people who have recently traveled to areas with Zika outbreaks.

Zika is spread primarily by mosquito bites, as well as sex. There have been cases of Zika transmission through blood transfusion in Brazil.

The FDA works with other federal agencies to set screening standards.