Sexual transmission of Zika Virus
On February 5, 2016, the Centers for Disease Control and Prevention (CDC) published recommendations for preventing sexual transmission of the Zika virus.1 Release of the interim guidelines came after a case was reported in Dallas, TX, involving a woman thought to have acquired Zika virus infection after sex with an infected partner.2 The only other information about possible sexual transmission available at the time included a published report of transmission from a man to a woman and a published report of Zika virus detected in semen of a man with hematospermia.3
On February 23, after receiving 14 additional reports of suspected sexual transmission of Zika virus, the CDC updated its guidelines on preventing sexual transmission of Zika.3,4 The 14 women included some who were pregnant. Two of the women had laboratory-confirmed Zika virus infection. Infection was considered probable in 4 others and had been excluded in 2, while information was pending for the remaining cases.
Information from the CDC notes that all men involved in known cases of likely sexual transmission had symptoms of Zika virus infection. However, virus transmission can occur before and after symptoms develop. In one case, it appears that the virus was sexually transmitted a few days before the man became symptomatic.
Only about 20% of people who are infected with the Zika virus develop the classic symptoms, which include fever, rash, joint pain, and conjunctivitis. It is not known if men infected with the virus but who are asymptomatic have the virus in their semen or if they can transmit the virus through sex.
It is known that the virus can persist in semen longer than it is present in blood, although how long the virus remains in the semen is not known. In a patient who developed signs of Zika virus infection after returning home to England from a trip to French Polynesia, Zika virus RNA was detected in semen when RT-PCR testing was performed at 27 and 62 days after the man first showed signs of infection.5 Serum and urine samples tested negative for the virus at both of those follow-up intervals.
It is also not known whether an infected woman can transmit the virus to sex partners or if transmission can occur with oral sex through exchange of bodily fluids, including semen, saliva, and vaginal fluids. Nor is it known if the risk of congenital infection is different when a pregnant woman acquires Zika infection through sex versus by a mosquito bite.