Unlike other vector-borne diseases such as dengue, yellow fever, and chikungunya, Zika can be spread through the traditional mosquito bite and through sexual transmission. To help stop the spread of Zika through sexual transmission, it is important to understand the risks of Zika as a sexually transmitted disease (STD) and to take proactive measures to protect yourself.
Despite mosquito-borne transmission dwindling over the winter in the majority of the U.S., the risk of Zika as an STD will not waver, particularly from the 40 million people that travel between the continental U.S. and Zika-affected areas each year. This has some people wondering: Will there be a Zika epidemic like we’ve seen with HIV?
Low Risk of a Zika STD Epidemic: Long story short, the risk of a Zika virus outbreak due to sexual transmission alone is low. In order for a pathogen (e.g., bacteria, virus) to result in an epidemic, an infected individual must, on average, infect more than one other individual. Although research is ongoing, Zika would need to be twice as infectious as HIV, and an individual would need to remain infectious for over one year before we approach this threshold. Fortunately, this is not what has been observed to date, suggesting the risk of a Zika epidemic driven solely by sexual transmission (no mosquito-borne transmission) is low.
“Low Risk” does not mean “No Risk”: Just because the risk of a sexually-transmitted Zika epidemic is low for the community as a whole, this does not mean that there is no risk at the individual level. As with any other STD, your risk of contracting Zika via sexual transmission is dependent on your sexual behavior and that of your partner. If an area has individuals with higher sexual activity, both in regards to frequency as well as number of partners, there may be an increase in the likelihood of localized Zika outbreaks due to sexual transmission. Therefore, individuals and partners must take responsibility for stopping the sexual transmission of Zika virus.
Protect Yourself from Sexual Transmission of the Zika Virus: Studies suggest that Zika can be transmitted via all forms of sex, regardless of gender, and even when the infected individual shows no symptoms.[3, 4, 5] With only ~20% of infected individuals experiencing symptoms, this underscores the need to be mindful of sexual behavior.
Although research is ongoing, current observations about the persistence of the virus in semen and vaginal fluid serve as the foundation for the CDC’s guidance for protecting against sexual transmission. Regardless of whether you and your partner are looking to conceive, or if you are solely focused on preventing sexual transmission of Zika, the CDC guidance remains the same:
- Abstain from sex for 6 months for men, and 8 weeks for women, from the time of last possible exposure, or
- Use condoms consistently and correctly for the same time periods.
As mosquito season begins to wane in much of the U.S., it seems that the interest and urgency for Zika control measures has followed suit. But given what we know about Zika as an STD and the number of travelers returning from Zika-affected areas, it is important for each person and their partner to understand that the risk of contracting Zika does not end with the mosquito.
Author: Dr. Jenn Kruk, Molecular Biologist, IEM
 Laith Yakob, Adam Kucharski, Stephane Hue, W John Edmunds. Low risk of sexually-transmitted Zika virus outbreak. Vol 16, No. 10, p1100–1102, October 2016. DOI: http://dx.doi.org/10.1016/S1473-3099(16)30324-3
 Brooks RB, Carlos MP, Myers RA, et al. Likely Sexual Transmission of Zika Virus from a Man with No Symptoms of Infection — Maryland, 2016. MMWR Morb Mortal Wkly Rep 2016;65:915–916. DOI: http://dx.doi.org/10.15585/mmwr.mm6534e2
 Davidson A, Slavinski S, Komoto K, Rakeman J, Weiss D. Suspected Female-to-Male Sexual Transmission of Zika Virus — New York City, 2016. MMWR Morb Mortal Wkly Rep 2016;65:716–717. DOI: http://dx.doi.org/10.15585/mmwr.mm6528e2
 Deckard DT, Chung WM, Brooks JT, et al. Male-to-Male Sexual Transmission of Zika Virus — Texas, January 2016. MMWR Morb Mortal Wkly Rep 2016;65:372–374. DOI: http://dx.doi.org/10.15585/mmwr.mm6514a3
 Petersen EE, Meaney-Delman D, Neblett-Fanfair R, et al. Update: Interim Guidance for Preconception Counseling and Prevention of Sexual Transmission of Zika Virus for Persons with Possible Zika Virus Exposure — United States, September 2016. MMWR Morb Mortal Wkly Rep 2016;65:1077-1081. DOI: http://dx.doi.org/10.15585/mmwr.mm6539e1