NEW YORK • The first case of female-to-male sexual transmission of the Zika virus has been documented in New York City, raising the prospect that the disease could spread more widely beyond the countries where it is already endemic and largely transmitted by mosquitoes.
For months, there has been growing concern about the possible danger of sexual transmission, but until now the virus has been thought to pass only from men to women, or between two men.
"This represents the first reported occurrence of female-to-male sexual transmission of Zika virus," said a report last Friday from the federal Centres for Disease Control and Prevention and the New York City Department of Health and Mental Hygiene.
The evidence of a previously undocumented transmission means is the latest twist in an outbreak that continues to baffle and surprise experts. It is prompting officials to rethink, once again, the guidance for healthcare providers and the general public on how to limit the danger of infection as the pool of those who could be at risk widens.
Zika can pose a dire risk to pregnant women. It targets developing nerve cells in foetuses and can lead to a birth defect called microcephaly, in which babies are born with abnormally small heads and brain damage. It also could cause developmental problems after birth.
Zika is primarily transmitted by the yellow fever mosquito, Aedes aegypti, which thrives in warm, tropical climates. But 11 countries have documented cases of sexual transmission from a man to a woman.
The New York case is the first in which a man was infected by a woman, and it raises the prospect that other men - with no travel history to Zika-affected areas and no reason to suspect that they might have the virus - could become infected and pass the virus on, creating a new chain of transmission.
In the report, researchers found that a man, who is in his 20s and did not travel outside the United States during the year before his illness, contracted the virus after one instance of vaginal intercourse, without a condom, with a woman who had recently returned from a country where the virus is endemic.
If the virus was passed along through vaginal fluid, there is very little information on how long it might persist there or how great the risk of transmission during intercourse is.
The report cites a recent study of non-human primates where three non-pregnant females were found to have the virus in vaginal fluid for up to seven days after exposure.
"Further studies are needed to determine if the virus is also found in the vaginal fluid of humans and, if so, for how long," the report said.
NEW YORK TIMES