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A doctor draw blood from Luana, who was born with microcephaly, at the Oswaldo Cruz Hospital in Recife, Brazil, Thursday, Jan. 28, 2016. Photograph by Felipe Dana, AP

Can We Keep Zika Out of the US Blood Supply?

If Zika virus comes to the United States, will the US blood supply be at risk?

Because the disease has demonstrated that it can pass via blood from mother to fetus, and via other bodily fluids between sexual partners, the question lurks in the back of most discussions of Zika’s likely arrival on the US mainland. And because there is not now a test for donated blood, keeping the virus out of the blood supply relies on people adhering to restrictions published by the Food and Drug Administration that ask travelers to defer donating for a period of time—an imprecise deterrent, but currently as good as it gets.

The concern for the blood supply is reasonable. In 2002, when West Nile virus was newly arrived in the United States, transfusions given to a teenage accident victim—who died of her injuries, and became an organ donor—caused that disease to pass to all four recipients of her organs. Dengue, another mosquito-borne illness that is burgeoning in Central and South America and has become established in south Florida, has also passed between blood donors and recipients, though there are only a few cases on record. And Zika virus was identified in 3 percent of donated blood in French Polynesia in late 2013 and early 2014, when the virus first landed in that area.

The concern has been sharpened by a new analysis, published Wednesday in the journal PLoS Currents Outbreaks, that plots the range of the mosquito species known to carry Zika against the numbers of travelers who arrive from the Zika zone. The researchers—from several US government agencies, North Carolina State University and University of Arizona, and Durham University in England—predicted that cities within the mosquito’s range are at highest risk of local transmission of Zika if they have international airports, or airports receiving connecting flights from those hubs. Other cities receiving large numbers of travelers from the Zika transmission zone were at moderate or lower risk if they fell near the edge of the mosquito’s range. So, for instance, Miami, Orlando, Jacksonville, Tallahassee, and New Orleans were at high risk of receiving the disease; New York, Atlanta and Houston were at moderate risk, and Dallas, Denver and Los Angeles at low risk.

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A map of cities most at risk for arrival and local transmission of Zika virus. Graphic from Monaghan et al., PLoS Current Outbreaks, March 16, 2016.

What was jaw-dropping in the study, though, were the sheer numbers of people who arrive in US cities from the Zika transmission zone: up to 1 million per month in Miami and New York, 500,000 per month in Atlanta, Houston, New York and Dallas, and millions per month through the ground border crossings of San Diego, El Paso and Laredo.

To prevent Zika contaminating the blood supply, the FDA issued guidelines last month addressing blood donation and this month regarding donated cells and tissues. For blood donation, the agency recommended that blood agencies ask people to defer donation for four weeks after experiencing Zika symptoms, traveling in the Zika transmission zone,  or having sex with a man who either had the symptoms or traveled in the Zika zone. For tissues such as ligaments and corneas, and cells (which include sperm and eggs), the agency extended the deferral to six months. The FDA has not placed any restrictions on donation of solid organs, arguing that because they are both life-saving and in short supply, the benefit outweighs the risk.

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Blood donations. Photograph by MikeHT, Flickr (CC).

Dr. Matthew Kuehnert, who is director of the office of blood, organ and other tissue safety at the Centers for Disease Control and Prevention, and is serving as the lead for the blood safety team in the CDC’S Zika response, said knowing how far to go to protect the blood supply is challenging because data is so sparse.

“There is little that we know about transfusion transmission of Zika, although I think we should assume it can happen,” he said by phone. “From the data that has been collected on Zika, about 80 percent of people don’t know they are infected. There is a period of viremia”—when virus circulates in the blood—”but we don’t know how long that viremia is. It is thought to be 7-10 days, but as we start to collect more data we may find it is longer than that.”

“It is possible we could get a transfusion or transplant transmission case before we even know local transmission of Zika is occurring.”

Those considerations apply in areas where Zika is not yet locally established. Where it is—which in the United States is Puerto Rico (160 cases as of March 9), American Samoa (13 cases) and the Virgin Islands (1 case)—blood is assumed to be a risk, and workarounds are being urgently sought. Because there is no test for Zika in donated blood—an approved test is “weeks to months away,” Kuehnert said—the only alternative is to use what are called “pathogen reduction” treatments, which inactivate viruses. Currently, pathogen reduction can only be used on platelets and plasma; red blood cells can be altered by pathogen reduction, and authorities are urgently searching for better techniques..

In a sign of how quickly an epidemic can upset the balance of blood supplies, Puerto Rico is now receiving outsourced blood from the US mainland, via a joint effort of three blood-collection agencies—the  American Red Cross, Blood Centers of America, and America’s Blood Centers—and the Department of Health and Human Services. The CDC estimates the current need for clean blood and blood products in Puerto Rico is 2,500 units of red blood cells, and an additional 1,000 units of other blood products, every week.

Despite the protections put in place by the FDA, public health authorities are braced for the possibility that transfusion-associated Zika could begin occurring in the United States. “This could happen at any time,” Kuehnert acknowledged.

He added: “It is possible we could get a transfusion or transplant transmission case before we even know local transmission of Zika is occurring,” because the illness that necessitates a transfusion—or the immunosuppressive drugs that transplants recipients take—make them more vulnerable to disease. “We are doing a lot of work to be prepared.”