Though bite of infectedmosquito is its primary mode of spread, since 2011, several case reports have
- Suggested Zika can be sexually transmitted.
- Documented Zika’s prolonged presence in semen of infected men.
In August 2016, the WHO () listed a total of 17 published reports on possible sexual transmission of Zika and 8 others on its presence in semen. Thus, as of Oct 2016, there’s plenty of scientific evidence that it’s possible for a Zika-infected man to infect a previously uninfected woman during sexual intercourse, in which case a fetus could also be affected. In other words, counting on a woman remaining uninfected following sex with a Zika-infected man is highly risky, especially for the fetus.
Reports Of Sexual Transmission From Symptomatic Males To Females
In each of these cases, the previously uninfected women developed symptoms suggestive of Zika even though they hadn’t been exposed to Zika-infected mosquitoes, i.e., highly likely they were infected through sexual transmission.
Cases reported from Argentina and France (), Canada ( ), Chile ( ), France, where in one case the suspected route was oral sex ( ) while the other case suggested male to female sexual transmission occurred 32 to 41 days after the man got infected with Zika ( ), Germany ( ), Italy ( ), a case where Zika virus RNA was found in the man’s semen even 62 days after first symptoms of infection, New Zealand ( ), a case where semen samples from the man tested positive for Zika virus RNA even 76 days after symptom onset and only tested negative on days 99 and 117, Peru ( ), Spain ( ), USA ( , , , ).
Other Reports Of Sexual Transmission Include
- Asymptomatic male to female, one each in France ( ) and USA ( ). Since ~80% of Zika-infected people remain asymptomatic ( ), prolonged presence of potentially infectious Zika in semen makes its sexual transmission a very important means of spreading through the population. Data also shows a pregnant woman being asymptomatic doesn’t preclude Zika virus from affecting the fetus.
- One case of male to male transmission (anal sex), in Texas, USA ( ).
- One case of female to male transmission in New York City, USA ( ).
Documented Cases Of Zika’s Presence In Semen
Live virus: Researchers were able to isolate Zika virus from semen
- In one case from the 2013 Zika outbreak ( ) two weeks after self-reported symptoms started.
- In a French case where semen virus load was 100000 times that in blood ( ) two weeks after self-reported symptoms started.
- Even 62 days after first fever symptom in a case from Scotland ( ).
Virus RNA: Detectable in a Netherlands patient up to 47 days after symptom onset (), 80 ( ) and 93 days ( ) from two cases in France, and even 181 ( ) and 188 days ( ) in two cases from Italy.
These data suggest live virus is not only present in semen of Zika-infected men but can also stay there for extended periods of time. This is why the WHO recommends () that
- In regions with active Zika virus transmission,
‘Pregnant women should practice safer sex or abstain from sexual activity for at least the whole duration of the pregnancy. Their partners should also be informed about this recommendation.’
- And in regions with no active Zika virus transmission,
‘a. Men and women returning from areas where transmission of Zika virus is known to occur should adopt safer sex practices or consider abstinence for at least 6 months upon return to prevent Zika virus infection through sexual transmission.
b. Couples or women planning a pregnancy, who are returning from areas where transmission of Zika virus is known to occur, are advised to wait at least 6 months before trying to conceive to ensure that possible Zika virus infection has cleared.
c. Sexual partners of pregnant women, returning from areas where transmission of Zika virus is known to occur, should be advised to practice safer sex or abstain from sexual activity for at least the whole duration of the pregnancy.’
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