Can Zika be considered a sexually transmitted infection?
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.
Due to the suspected association between in utero exposure to Zika virus infection and congenital microcephaly, the CDC recommends women who are pregnant should speak to their physician about preventing infection and if they think they have a male partner who may have or was known to have Zika virus infection. The CDC has published guidelines for evaluation and testing of pregnant women.
Women with male partners who are living in or who have traveled to an area with Zika are advised to either use condoms correctly any time they have insertive sex (vaginal, anal, or oral) or to abstain from sex during their pregnancies.
The CDC recommends male partners of pregnant women should be using measures to prevent mosquito bites and that men who live in or have traveled to an area of active Zika virus transmission and who have a pregnant sex partner should consistently and correctly use condoms during sex or abstain from sex during the duration of the pregnancy.
Noting the lack of knowledge about how long Zika remains in the semen of infected men and whether infected men who remained asymptomatic carry Zika in their semen, women who are trying to get pregnant are also encouraged to speak to their healthcare provider and be prepared to discuss their partner’s travel history, whether he used repellents to prevent mosquito bites, and if they had sex without the protection of a condom. Although there are tests available to detect Zika virus in semen, they are not widely available and interpretation of the results is unclear at the present time.
Captain David M. Morens, MD, is Senior Advisor to the Director, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD. He said that while cases are rare, sexual transmission of other viruses has been recognized previously. In addition, he noted that the immune-privileged state of the gonads allows for virus survival.
“It appears that sexual transmission may occur more often with the Zika virus than with other viruses. This is an observation, however, that needs to be confirmed,” Dr. Morens said.
Information on Zika virus for health care providers, including information specific to obstetrical care providers, can be accessed at http://www.cdc.gov/zika/hc-providers/index.html.
1. Oster AM, Brooks JT, Stryker JE, et al. Interim guidelines for prevention of sexual transmission of Zika virus-United States, 2016. MMWR Morb Mortal Wkly Rep. 2016;65(5):120-121.
2. Dallas County Health and Human Services. DCHHS reports first Zika virus case in Dallas County acquired through sexual transmission. February 2, 2016. Dallas, TX: Dallas County Health and Human Services; 2016. http://www.dallascounty.org/department/hhs/documents/February2016Newsletter.pdf.
3. Update: Interim guidelines for prevention of sexual transmission of Zika virus - United States, 2016. Available at: http://emergency.cdc.gov/han/han00388.asp. Accessed March 5, 2016.
4. Hills SL, Russell K, Hennessey M, et al. Transmission of Zika virus through sexual contact with travelers to areas of ongoing transmission – Continental United States, 2016. MMWR Morb Mortal Wkly Rep. 2016;65(8):215-216.
5. Atkinson B, Hearn P, Afrough B, et al. Detection of Zika virus in semen [letter]. Emerg Infect Dis. 2016;22.Epub February 11, 2016]