It has been long known that men who are infected with Zika can spread the virus to their sex partners. This was the case of the American researcher who was infected by the mosquito-borne virus while working in Senegal whose wife developed symptoms of the disease after his return.

It appears that women infected with Zika can also spread the virus to their sexual partner.

The U.S. Centers for Disease Control and Prevention (CDC) reported on Friday of the first known case of female-to-male Zika infection, which was detected in New York City.

Alexander Davidson, from the New York City Department of Health and Mental Hygiene in New York, and colleagues reported that the case involved a woman in her 20s who had travelled to a place where the Zika virus is spreading.

The woman had vaginal sex with a male partner without using condom when she arrived home. She was eventually diagnosed with Zika when she suffered from fever, rash, fatigue and heavier period than usual. A week later, the male partner also developed symptoms and tested positive for the virus.

Although the case involved a woman infecting men, CDC said that this suggests transmission can also spread between two women and urged increased caution for pregnant women with female sexual partners who have visited or lived in Zika-infected places.

"Women who have pregnant women for sexual partners should abstain [from sex] through the duration of the pregnancy," said CDC senior medical advisor John Brooks. "There has not been a documented case of female to female transmission yet but we believe this is the right thing to do to provide the best possible protection."

Most of those who get infected with the virus do not get sick, or only develop mild illness but the virus can cause serious problems in pregnant women and their unborn child. Pregnant women who get infected with the virus faces increased likelihood of bearing children with birth defects such as microcephaly. In rare cases, Zika can also cause neurological conditions in adults.

"This case represents the first reported occurrence of female-to-male sexual transmission of Zika virus," Davidson and colleagues reported in the CDC journal Morbidity and Mortality Weekly Report on July 15.

"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. Ongoing surveillance is needed to determine the risk for transmission of Zika virus infection from a female to her sexual partners."