All blood donations in the U.S. should be tested for the Zika virus, the Food and Drug Administration said Friday.

The recommendation indicates the federal health agency sees Zika as a much broader threat now compared to six months ago, when it recommended screening blood for Zika only in areas with active Zika virus transmission.

"There is still much uncertainty regarding the nature and extent of Zika virus transmission," said Peter Marks, director of the FDA's Center for Biologics Evaluation and Research. "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 a transfusion."

More than 2,500 cases of Zika have been reported around the country, the majority travel-related. But the virus has been found to be spreading locally, through mosquitos, in three regions in Florida, heightening concerns of public health officials. The regions include Palm Beach, Tampa and Miami.

The virus causes relatively mild symptoms in adults, but can cause severe birth defects if pregnant women are infected. Health officials have warned pregnant women against traveling to the areas in Florida where the virus is mosquito-borne.