Guidance on sexual transmission of Zika virus and methods of prevention.
Zika virus and sexual transmission
The greatest likelihood of acquiring Zika virus infection is via the bite of an infected Aedes mosquito whilst travelling to a country or area with risk for Zika virus transmission. However, a small number of cases have occurred through sexual transmission.
The majority of reported cases of sexual transmission have involved transmission from a male to a female partner. Transmission from a female to a male sexual partner, and from a male to a male sexual partner has also been reported, whilst there is a theoretical risk of transmission from a female to a female sexual partner.
Sexual transmission can occur via vaginal sex, anal sex, oral sex and the sharing of sex toys. People infected with Zika virus can pass the virus through sex even when asymptomatic.
Zika virus has been shown to be present in semen and vaginal secretions. The virus persists longer in semen (3 months) than in the female genital tract (2 months), therefore the advice given to prevent sexual transmission is different for men and women.
Potential consequences of Zika virus sexual transmission
While Zika is usually an asymptomatic or mild illness for the majority of people, more importantly, it presents a significant risk to the developing fetus as it can cause serious birth defects. Infection in the first trimester of pregnancy appears to carry the greatest risk of these abnormalities, which can occur even if the woman had no symptoms at the time of her Zika infection. However, a risk exists throughout pregnancy.
It is therefore imperative that women who are pregnant take measures to avoid exposure to Zika virus throughout the duration of pregnancy, including during sexual contact.
Similarly, couples should take precautions to avoid a woman becoming pregnant during or shortly after having a possible Zika virus infection.
Barrier methods to prevent sexual transmission
There are recommended barrier methods to prevent sexual transmission of Zika virus from an individual who may have been exposed to Zika virus either as a traveller returning from a country or area with risk of Zika virus transmission or following previous unprotected sexual contact with a potentially infectious partner.
Barrier methods include:
- male or female condoms for penetrative sex (including sex toys)
- male or female condoms or dental dams for oral-genital or oral-anal sexual contact
- sex toys should not be shared
- to increase their effectiveness barrier methods should be used consistently and correctly, for the entire duration of sexual contact
Advice for individuals at greatest Zika virus risk
Pregnant women and women or couples considering pregnancy are advised to check the NaTHNaC country information pages and the A to Z listing for detailed country advice prior to travel.
Screening of asymptomatic travellers for Zika virus infection is not available on the NHS. Therefore, couples considering pregnancy in the very near future should consider whether they should avoid travel to a country or area with risk for Zika virus transmission, rather than delay conception for the recommended period (see below) after travel. This particularly includes couples in assisted conception programmes.
No specific sexual transmission precautions are required for travellers to countries with very low risk for Zika virus transmission.
This advice is summarised in an algorithm which is available here.
Advice for pregnant women and their sexual partners
Consistent use of barrier methods for vaginal, anal and oral sex during and after travel is advised to reduce the risk of sexual transmission which could result in the developing fetus becoming infected with Zika virus.
Barrier methods should be continued for the duration of the pregnancy and couples should use barrier methods during and after travel even in the absence of Zika virus symptoms.
Advice for couples considering pregnancy
Consistent use of effective contraception and consideration of barrier methods for vaginal, anal and oral sex during and after travel is advised to reduce the risk of conception and sexual transmission which could result in the developing fetus becoming infected with Zika virus.
These measures should be maintained for the following time periods even in the absence of Zika virus symptoms:
- if both partners travelled, for 3 months after last possible Zika virus exposure
- male traveller only, for 3 months after return or after last possible Zika virus exposure
- female traveller only, for 2 months after last possible Zika virus exposure
*Last possible Zika virus exposure is defined as the date of leaving an area with high or moderate Zika virus risk, or the date on which unprotected sexual contact with a potentially infectious partner took place.
Travelling to low risk countries/areas
- No specific precautions required
Individuals with further concerns regarding sexual transmission of Zika virus and options for contraception or barrier methods should contact their GP for advice.