First female-to-male sexual transmission of Zika reported in New York City

Zika virus may spread sexually from women to men, according to a case report released today by the Centers for Disease Control and Prevention. It is the first suspected instance of female-to-male sexual transmission of the disease, which can cause birth defects like microcephaly.

The primary patient in question is a New York City woman in her twenties, who had recently traveled to a country dealing with ongoing transmission of Zika virus. Upon returning from the trip, she had condomless sex with a male partner, and the next day, she developed fever, fatigue, rash and other signs of Zika. A DNA test two days later confirmed that she had Zika virus.

Her male partner, who had not traveled to a Zika-hit region, developed symptoms of the disease a week later.

The CDC has not changed its Zika-related advice for partners due to the case, but the incident raises new questions. The public health agency still recommends that persons with Zika abstain from sex or use condoms for vaginal, anal and oral intercourse — all of which have been linked to passing the disease.

The woman in this report also began menses a day after returning home, but it’s unclear if vaginal fluids or menstrual blood lead to exposure in her male partner. Early cases of male-to-female transmission involved hematospermia, blood in seminal fluid. This condition might increase the amount of virus in sexual excretions, though cases of male transmission without hematospermia have been reported too.

It’s also unknown how long the virus lasts in the female genital tract. One study in women found the virus in the cervix and genitals three days after illness onset, while another investigation in female rhesus monkeys stated the virus can last in these regions up to seven days.

“Further studies are needed to determine the characteristics of Zika virus shedding in the genital tract and vaginal fluid of humans,” the report stated. The announcement was published today in the CDC’s Morbidity and Mortality Weekly Report.