The U.S. Food and Drug Administration (FDA) has directed blood collection facilities to begin screening all donated blood and blood components for the Zika virus. Currently, Florida and Puerto Rico and a few other areas are already performing screening.
Though most people infected with Zika do not become ill or have a mild illness and recover fully, the infection can cause serious consequences for babies born to women who are exposed to the virus while pregnant, such as microcephaly (smaller than expected head) and other birth defects.
While no transmissions of Zika through blood transfusions have been documented in the U.S. to date, there have been four probable transfusion-related cases in Brazil. In 2014, during an outbreak in French Polynesia, nearly 3% of blood donors who had no symptoms tested positive for the virus, suggesting the risk of spreading Zika through blood transfusions.
Earlier this year, the FDA had advised that people at risk of Zika infection, such as those who had traveled to areas where Zika is active, be deferred from donating blood. This earlier guidance is now revised to include universal screening of blood donations to further reduce the risk of transmitting the virus through blood transfusions.
"As new scientific…information regarding Zika virus has become available, it's clear that additional precautionary measures are necessary," said Luciana Borio, MD, the FDA's Acting Chief Scientist in a press release.
So far, only Florida and Puerto Rico have reported local transmission of the mosquito-borne Zika virus in the U.S., but more areas are expected to be affected. For the latest information, see the CDC's Map of Zika in the United States. The Aedes mosquito that carries the virus is found mainly in the southern U.S. Eleven states in the south will begin screening blood donations for Zika within the next month and the rest of the states are required to begin screening within 3 months.
As labs at blood donor centers ramp up testing, FDA officials anticipate no issues with testing supplies. Earlier this year, the FDA approved two investigational tests for use to screen donated blood for Zika. The tests were approved under an "investigational new device (IND)" protocol and did not go through the standard regulatory process prior to implementation, which can be time-consuming. The tests screen for the presence of the virus by detecting its genetic material (RNA). Units of blood that test positive for the virus are removed from the supply and not used for transfusions.
One of the challenges in containing the disease is that most people infected with Zika (about 80%) have no symptoms and don't know they are infected and can spread the disease. Though primarily spread through bites of mosquitos, scientists have learned that the virus can be transmitted through sexual contact. They are currently studying how long the virus may be transmitted in this way. There has also been one case reported in a caregiver of a patient infected with Zika and a case in which a laboratory employee contracted the disease.
"There is still much uncertainty regarding the nature and extent of Zika virus transmission," said Peter Marks, M.D., Ph.D., director of the FDA's Center for Biologics Evaluation and Research in a press 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."