First female to male sexual transmission of Zika virus documented in New York.

Yet another very important update on sexual transmission of Zika virus from CDC was published online in CDC's Morbidity and Mortality Weekly Report[1]

Till now it was known that sexual transmission of ZIKA virus only takes place from male to female partner. But, The New York City Department of Health and Mental Hygiene (DOHMH) today identified the first case of a female transmitting the Zika virus to a man through sex in New York city.

This surprising new announcement have prompted the CDC to update its guidelines on the sexual mode of transmission of the virus.

A 20-year-old non-pregnant woman had condomless vaginal intercourse with male partner on the day she returned from a country where Zika virus infection is ongoing. She was completely symptomless on the day of return, but was down with Zika-like symptoms, including fever, rash, fatigue and muscle pain, along with numbness and tingling in her fingers and toes. On the next day she visited her primary health care provider, who confirmed the illness as Zika virus after getting the results of her urine and blood test. ((rRT-PCR). 

A week after the sexual contact, the male partner also had similar symptoms and was also diagnosed with Zika infection. On detailed history he ruled out other mode of Zika transmission. He has not travelled outside the country since 1 year, only had one sexual encounter since a week and did not have any mosquito bite.

Both the partners tested negative for Zika virus IgM antibodies by the CDC Zika MAC-ELISA assay performed at the New York State Department of Health Wadsworth Center.

CDC report concluded that “The timing and sequence of events support female-to-male Zika virus transmission through condomless vaginal intercourse.” The woman was most likely viremic when she had sex with her partner, and the virus was transmitted through uretral mucosa or penile abrasion or cut from woman’s vaginal or menstrual blood.   

A case report published on May 2016 in Lancet has already documented the presence of Zika virus in female genital tract.[2] Non-Human studies in primates have shown the presence of the virus in genital tract up to 7 days after subcutaneous inoculation.[3]

This case is very important from public health perspective as until now, it was assumed that the Virus is transmitted from a male partner to a receptive partner, now ongoing surveillance will be needed to combat the additional risk of reverse transmission. CDC is also advising protection for pregnant women with female sex partners who might have travelled to Zika endemic areas, though woman to woman transmission is not known till now.

The report stressed the need for further studies to determine the amount of time of virus survives in female genital tract.

The Aedes aegypti mosquitos still is the major source of infection.

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[1] http://www.cdc.gov/mmwr/volumes/65/wr/mm6528e2.htm?s_cid=mm6528e2_w

[2] http://www.thelancet.com/journals/laninf/article/PIIS1473-3099%2816%2930193-1/fulltext

[3] Dudley DM, Aliota MT, Mohr EL, et al. A rhesus macaque model of Asian-lineage Zika virus infection. Nat Commun 2016;7:12204