A suspected case of sexual transmission of the Zika virus from a female to a male has occurred in New York City, according to the New York City Department of Health and Mental Hygiene (DOHMH).

“This case represents the first reported occurrence of female-to-male sexual transmission of Zika virus,” Alexander Davidson of the DOHMH and his coauthors stated in the CDC’s Morbidity and Mortality Weekly Report . “Current guidance to prevent sexual transmission of Zika virus is based on the assumption that transmission occurs from a male partner to a receptive partner.”

The woman, reportedly in her twenties and not pregnant at the time of infection, had traveled to a region experiencing high volumes of Zika virus transmission. Upon returning home, the woman engaged in condomless vaginal intercourse with her male partner, and subsequently developed symptoms consistent with a Zika virus infection. Three days after symptom onset, her primary care provider took blood and urine samples, from which a Zika virus infection was confirmed. ( MMWR Morb Mortal Wkly Rep. 2016 Jul 15. doi: 10.15585/mmwr.mm6528e2 )

A week after the sexual encounter, her partner – also in his twenties – began experiencing symptoms of Zika virus infection. Three days after the onset of his symptoms, he went to the same primary care provider as the woman. He confirmed that he had not traveled outside of the United States in the last year, had engaged in condomless vaginal sex with just one individual (the aforementioned female), had no blood on his penis to indicate vaginal bleeding or the presence of open lesions, and had no mosquito bites in the previous week.

“The timing and sequence of events support female-to-male Zika virus transmission through condomless vaginal intercourse,” the coauthors conclude, adding that “virus present in either vaginal fluids or menstrual blood might have been transmitted during exposure to her male partner’s urethral mucosa or undetected abrasions on his penis.”

Both the female and male were tested via real-time reverse transcription–polymerase chain reaction (rRT-PCR), with serum testing done via the Zika immunoglobulin M antibody capture enzyme-linked immunosorbent assay (Zika MAC-ELISA). The rRT-PCR testing showed Zika virus RNA in the woman’s serum, despite being collected three days after the sexual encounter, meaning she was viremic at the time. Studies on nonhuman primates have shown that Zika virus RNA can remain present in vaginal fluid for up to a week, according to the report.

The CDC is cautioning pregnant women against travel to Zika-heavy areas, in particular the 2016 Summer Olympic Games in Rio de Janeiro. Health care providers who receive patients with Zika-like symptoms should ask if the patient has had sexual contact with someone who has traveled to an affected region, if the patient did not travel to such a region.


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