Authorities in Brazil, where a Zika outbreak has been linked to severe birth defects, on Thursday disclosed two cases of transmission tied to blood transfusions, adding to concerns over the spread of the virus.
The virus, spreading quickly across Latin America and the Caribbean, is usually transmitted by the bite of a mosquito.
Marcelo Addas Carvalho, the doctor who is the director of the blood center at the University of Campinas near Sao Paulo, said genetic testing confirmed that a man who received a blood transfusion using blood donated by another man infected with Zika in March 2015 became infected with the virus, although he did not develop symptoms.
Carvalho said another man, who had suffered gunshot wounds, also became infected with Zika after receiving multiple blood transfusions that included blood donated by an infected person in April 2015.
Carvalho said that infection probably was caused by the transfusion but genetic tests have not yet been conducted to confirm it. He said it was very unlikely the infection was caused by a mosquito bite because the patient was in a hospital intensive care unit for three months. The patient later died from his gunshot wounds and not the Zika infection, health officials and Carvalho said.
“Transmission of the virus through blood transfusion is very rare and not an important factor in the epidemic. Governments and society in general should focus on eliminating the mosquito, which is the main form of transmission,” Carvalho said.
The Brazil cases, along with a reported case of sexual transmission of the virus in Texas add a new dimension to efforts to limit Zika’s spread.
The cases have emerged at an awkward time because Rio de Janeiro is preparing to host the Olympic Games in August when tens of thousands of athletes and tourists were expected to visit Brazil’s second largest city.
Brazil is investigating more than 4,000 suspected cases of microcephaly, a condition in which infants are born with abnormally small heads and can suffer developmental problems, that may be linked to the outbreak.
Scientists have begun to study whether Zika infection in pregnancy can cause microcephaly. The World Health Organization, citing strong suspicions of a link between the two and the spike in cases in Brazil, declared a global health emergency on Monday.
Sexual contact and blood transfusions as modes of transmission of the virus have been matters of concern for experts since the beginning of the outbreak, said Dr. William Schaffner, an infectious diseases expert at the Vanderbilt University School of Medicine in Nashville, Tennessee.
But Schaffner questioned whether either will lead to widespread transmission of Zika.
“A little bit of transmission? Sure,” Schaffner said. “But the main engine of transmission that has led this virus to be spread widely throughout Central and South America and the Caribbean is, of course, the mosquito.”
Procedures for blood donations have been tightened in the countries including Brazil to protect blood supplies from Zika. U.S. health officials are still working on national guidelines.
Following word of the Texas case on Tuesday, U.S. health officials urged the use of condoms to prevent spreading sexually transmitted infections.
Brazil said it was reinforcing instructions to blood banks that people infected with Zika or dengue not be permitted to donate blood for 30 days after full recovery from the active stage of Zika infection.
The American Red Cross has urged prospective donors who have visited Zika outbreak zones to wait at least 28 days before giving blood, but said the risk of transmitting the virus through blood donations was “extremely” low in the continental United States.
It asked donors who give blood and subsequently develop symptoms consistent with Zika within 14 days to notify the Red Cross so the product can be quarantined.
In the Texas case, a person in Dallas became infected with Zika after having sex with another person who had traveled in Venezuela, where the virus is circulating.
Dallas County health officials said on Thursday both those people have fully recovered from the virus.
Schaffner said uncertainties remain about sexual transmission of the virus, including how long a person might be able to transmit it or whether an infected person must have had symptomatic Zika in order to be able to transmit Zika through sex. Most infected people do not develop any symptoms.
While health authorities have not provided such details, Schaffner said he suspected a man transmitted Zika to a woman.
“We don’t know whether it can move from a woman to a man. We assume also that if a man can transmit it to a woman, that a man could also transmit it to another man,” Schaffner said.
New York Governor Andrew Cuomo on Thursday expanded his state’s free Zika testing to include all pregnant women who have traveled to countries where people have been infected.
Florida Governor Rick Scott declared a public health emergency on Wednesday in four counties with travel-related cases of the Zika virus. Scott extended his order to a fifth county on Thursday. He has also ordered increased mosquito control efforts in some of the southeastern state’s most heavily populated locales including Miami and Tampa.