Liz Szabo

USA TODAY

In response to the mosquito-borne Zika outbreak, the American Red Cross is asking people to avoid donating blood if they traveled to Latin America or the Caribbean in the past 28 days.

Blood donors who develop symptoms of Zika within two weeks of donating blood should contact the Red Cross within immediately so their blood can be quarantined, the organization said in a statement Wednesday.

“The American Red Cross is dedicated to providing the safest, most reliable blood products possible to patients in need," said Susan Stramer, vice president of scientific affairs at the American Red Cross. "The Red Cross continues to use safety measures to protect the blood supply from Zika and other mosquito-borne viruses."

The announcement comes two days after a similar recommendation by the American Association of Blood Banks, which says the virus is believed to remain in the blood for less than 28 days.

The Canadian Blood Services said Wednesday it is barring people from giving blood within 21 days of traveling outside of Canada, the continental USA and Europe.

Blood suppliers currently test for diseases including HIV, hepatitis, West Nile virus and the parasite that causes malaria. There are no commercial tests for Zika virus, said Anne Winkler, medical director of the transfusion service at Grady Health System in Atlanta.

One advantage to the Red Cross' voluntary approach: it can begin immediately. Changing the questionnaire given to potential blood donors to ask about recent travel to Zika-affected areas would take much longer, since those forms must be reviewed by the Food and Drug Administration, Winkler said.

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Unlike the flu, the virus cannot be spread from person to person. Mosquitoes that bite an infected person can spread it to future victims.

Because the virus is not spreading among local mosquitoes in the continental USA, the risk of contracting Zika through a blood transfusion here is "extremely low," said Robert Glatter, an emergency physician at Lenox Hill Hospital in New York City.

More than 30 Americans have been diagnosed with Zika after traveling to Latin America or the Caribbean. The risk that those travelers could spread the diseases to others is remote because mosquitoes don't bite in the winter, Glatter said.

The Red Cross only collects blood from people who are "healthy and feeling well at the time of donation." But four out of five people with Zika infections experience no symptoms of disease. Those who do often report mild illness, including low fever, rash, pink eye, joint pain and headache, according to the World Health Organization.

During an outbreak of Zika in French Polynesia from 2013 to 2014, doctors found the virus in 3% of blood donors without any symptoms, according to a study published in October in Emerging Infectious Diseases.

Scientists in Brazil are evaluating a possible case of Zika virus spread through a blood transfusion, according to the American Association of Blood Banks. Dengue fever, a virus spread through the same Aedes mosquito that transmits Zika, is known to spread through blood transfusion.

Infectious disease specialist Peter Hotez said the Red Cross is taking a "reasonable" approach to reduce the risk of Zika in the organization's blood supply.

Asking people to avoid giving blood within 28 days of travel will reduce the blood supply, but not by much, Winkler said. The policy will reduce summer blood supplies by 1.17% and winter blood supplies by 2.27%, according to the American Association of Blood Banks.

Policies could change as scientists learn more about the virus, said Kristy Murray, director of the Laboratory for Vector-Borne and Zoonotic Diseases at Baylor College of Medicine and Texas Children's Hospital in Houston.

"This is all constantly evolving," she said.