Doctors believe that a blood donor passed along the typically mosquito-borne virus in late January to two hospitalized patients who needed transfusions.
"These data show evidence for Zika virus transmission by means of [blood] platelet transfusion," reported a team led by Dr. Iara Motta, of the Jose Alencar Gomes da Silva National Cancer Institute in Rio de Janeiro, and Bryan Spencer of the American Red Cross in Dedham, Mass.
According to the researchers, the donor alerted the local blood bank of symptoms -- rash, eye pain and joint pain -- that had developed two days after donation. Lab tests confirmed that the blood was contaminated with Zika virus.
In the meantime, the blood had been transfused into two patients -- a 54-year-old woman with the bone marrow disorder myelofibrosis, and a 14-year-old girl battling leukemia. The Zika strains from the donor and the two recipients were a match, and the evidence appears to "strongly favor transfusion as the source of the infection," the authors reported Aug. 17 in the New England Journal of Medicine.
As often occurs, neither of the patients who received the donated blood came down with symptoms of Zika infection, the researchers noted.
The Zika virus is typically transmitted via mosquitoes and can cause a transient illness. It is most dangerous to pregnant women, due to the virus' link to microcephaly, a devastating birth defect where babies are born with smaller than normal heads and underdeveloped brains.
Health officials in the United States have already been preparing for the possibility of Zika transmission via blood transfusion. In March, the U.S. Food and Drug Administration approved an experimental test to check blood donations for the Zika virus.
"The availability of an investigational test to screen donated blood for Zika virus is an important step forward in maintaining the safety of the nation's blood supply," Dr. Peter Marks, director of the FDA's Center for Biologics Evaluation and Research, said at the time in an agency news release.
Wherever Zika virus transmission occurs, "blood collection establishments will be able to continue to collect blood and use the investigational screening test, minimizing disruption to the blood supply," he explained.
The FDA also recommends that anyone who has traveled recently to an area where the Zika virus is active refrain from donating blood.
In other recent news, Texas health officials on Monday reported what appears to be the first case of Zika infection traveling across state lines. A resident of that state who visited Miami recently has tested positive for the virus, state health officials said in a statement.
Things are much worse in the U.S. territory of Puerto Rico, where federal health officials declared a public health emergency on Friday because Zika is spreading so rapidly among residents there. The number of Zika cases there now total 10,690, with 1,035 of those being pregnant women.
The continental United States is also experiencing its first-ever local outbreak of Zika, in a one-square-mile Miami neighborhood called Wynwood. Florida health officials say there have been at least 28 local Zika infections.
The U.S. Centers for Disease Control and Prevention is urging pregnant women and their partners to stay away from Wynwood -- the first time the CDC has ever warned against travel to an American neighborhood for fear of an infectious disease.
The more than 1,800 Zika infections so far reported in the United States mainly have been linked to travel to countries with Zika outbreaks in Latin America or the Caribbean.
Most of the thousands of Zika infections recorded globally have so far occurred in Latin America and the Caribbean. Brazil, especially, has reported the vast majority of cases of Zika-linked microcephaly.
U.S. officials said they don't expect to see a Zika epidemic in the United States similar to those in Latin America. The reason: better insect control as well as window screens and air conditioning that should help curtail any outbreaks.
In addition to mosquitoes, the Zika virus can be transmitted through sex. These infections in the United States are thought to have occurred because the patients' partners had traveled to countries where Zika is circulating, the CDC said.
The CDC advises pregnant women not to travel to an area where active Zika transmission is ongoing, and to use insect repellent and wear long pants and long-sleeved shirts if they are in those areas. Partners of pregnant women are advised to use a condom to guard against sexual transmission during pregnancy.
The U.S. Centers for Disease Control and Prevention provides more information on mosquito-borne diseases.
This Q & A will tell you what you need to know about Zika.
To see the CDC list of sites where Zika virus is active and may pose a threat to pregnant women, click here.
Copyright © 2016 HealthDay. All rights reserved.