WASHINGTON (AP) – The Food and Drug Administration is recommending U.S. blood banks refuse donations from people who have travelled to countries where the Zika virus is active in the previous four weeks, part of guidelines meant to protect the blood supply from the mosquito-borne virus.

The agency recommends the same four-week deferral for people who have shown symptoms of the virus or had sexual contact with someone who has traveled to a Zika-affected region in the past three months.

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The recommendations follow similar measures taken earlier this month by the Red Cross and the American Association of Blood Banks, which have asked travelers to Zika outbreak countries to wait at least 28 days before donating blood.

While FDA officials stressed that there have been no reports of Zika entering the U.S. blood supply, they said transmission through blood is a real possibility.

“Based on the best available evidence, we believe the new recommendations will help reduce the risk of collecting blood and blood components from donors who may be infected with the Zika virus,” said FDA biologics director Dr. Peter Marks, in a statement.

Canadian blood officials have already taken similar steps, deferring donations from people who have travelled outside of Canada, the continental United States and Europe.

The virus is spreading rapidly through Latin America. While most people experience either mild or no symptoms, Zika is suspected of causing a devastating birth defect – babies born with abnormally small heads – and pregnant Americans are urged to avoid travel to affected areas.

One case in Texas is believed to have been transmitted through sex, and officials in Brazil, hard-hit by Zika, have recently reported finding the virus in saliva and urine.

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Federal health experts say more study is needed to determine whether Zika can spread through those body fluids. The main source of transmission remains mosquitoes.

Zika usually is transmitted through bites from a mosquito species that can be found in Florida, along the Gulf Coast and in states that border Mexico, among other regions.

Currently no local mosquito-borne Zika cases have been reported in U.S. states, but several cases have been reported in U.S. territories, including Puerto Rico, the U.S. Virgin Islands and American Samoa.

In those areas, the FDA recommends blood banks obtain whole blood donations from U.S. states that have not reported Zika transmission via mosquito.

If someone is actively infected, the U.S. government has a test that diagnoses Zika fairly well. But most people experience no symptoms or very mild ones, and the antibody test used to tell afterward if they were infected isn’t very accurate.

The Centers for Disease Control and Prevention is urging pregnant women or those trying to become pregnant not to travel to Zika-affected areas.

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