IQ2: Sexual transmission of Zika Virus


APRIL 2016: apx. 9 min. | The second episode of our Infectious Questions podcast continues its focus on Zika virus with our guest expert addressing questions around the sexual transmission of Zika.

IQ2: Sexual transmission of Zika Virus

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Rick Harp: Welcome to Infectious Questions, a public health podcast produced by the National Collaborating Centre for Infectious Diseases. NCCID helps those with infectious disease questions connect to those with the answers. Hello, I’m Rick Harp.

Shivoan Balakumar: And I’m Shivoan Balakumar. This episode continues our focus on Zika virus. Last week, we looked at the risks pregnant women potentially face when traveling to Zika affected areas. This week, our guest expert addresses questions around the sexual transmission of Zika.

Harp: Dr. Philippe Lagacé-Wiens is an assistant professor of Medical Microbiology and Infectious Disease at the University of Manitoba. He’s also a consultant to the Travel and Tropical Medicine Clinic of the Winnipeg Regional Health Authority.

Doctor, welcome back to Infectious Questions.

Dr. Philippe Lagacé-Wiens: Thank you.

Harp: Now, this week, we’re dealing with a question that came your way from a woman who had recently gone to the Caribbean with her partner. They had heard sexual transmission of Zika virus was a risk, a risk that’s since been confirmed. That, in turn, prompted her to ask how long she and her partner should wait before trying to have a baby. How would you address that?

Lagacé-Wiens: Thank you for that question. So, definitely, there have been a number of reports now, starting actually a couple years ago, that Zika virus could be transmitted sexually to an individual who had not been exposed at all. And that’s how it was first noticed, that travelers would come back and transmit it sexually to a place where there was no Zika virus circulating. And they since then have basically confirmed that this is the case; you can transmit this virus sexually.

In a couple that has traveled and is intending to become pregnant shortly after their travels, there are a number of recommendations that have been put out there. And they all come from data that is not the best quality of data, but it’s the best that we have right now. One of the challenges is, we don’t really have a good handle on how long this virus will stay in the human body.

We know that it stays in the blood for, at the outset, maybe two weeks after you start to get symptoms—so maybe three weeks after you travel to the endemic area—but we don’t know if it’s got other parts of the body that it can stay in for a while, both in the woman and in the man. And certainly in the man, what we’ve demonstrated is that the virus will persist in semen, so in secretions from the general urinary tract and in the prostate, for upwards of two months, and certainly have demonstrated it in semen about 62 days after an infection, and that’s the highest level of evidence that we have and it’s a single case, so it’s obviously low-level evidence but it’s what we have.

And so there’s obviously then, therefore, the risk that a man can transmit it to his wife upwards of two months after he has been infected. And an unknown risk that the woman might actually have this virus in parts of her body, maybe even in the ovaries, until two months as well. And that’s just basically inferring one from the other.

So the general rule, what the recommendation is for a couple who’s intending to become pregnant after having been potentially exposed, acknowledging that this virus can be asymptomatic in a lot of people, is in the range of two to three months after the exposure. And again, that’s only going by very limited evidence that we have. That’s why you see this broad two to three months answer to this sort of question (*Note – since recording this webcast, guidance on sexual transmission has been refined).

I personally have been following the guidelines that are set out by the Canadian Travel Advisory, which state two months, but it’s not unreasonable to say three months because other organizations are saying the same thing. And that only reflects the lack of knowledge that we have currently so we’re using fairly broad recommendations.

Harp: And remind us again: what percentage of cases are asymptomatic?

Lagacé-Wiens: About 80 per cent of cases are asymptomatic, and so it’s entirely possible that either one or the other of the partners have been infected, have the virus in their body (and, in the case of the man, have it in their prostate) and really not have had any symptoms at all. What we don’t know, interestingly, is whether or not an asymptomatic man can transmit it to his partner. The only cases that we have in the literature right now are all of symptomatic individuals transmitting it to their partner. Now, whether or not the absence of symptoms is indicative of a better control of the virus initially, and that maybe it doesn’t establish itself in the prostate or other organs of the body, is completely unknown. So we basically apply the same criteria to everybody.

How common is the sexual transmission of Zika virus?

Balakumar: Now, earlier in March, the WHO (World Health Organization) Director General, Dr. Margaret Chan, announced that reports and investigations from several countries strongly suggest that sexual transmission of the virus is more common than previously assumed. Could you comment on the research and findings that inform this statement, as well as some of the questions that are still unanswered in relation to current guidance in Canada?

Lagacé-Wiens: Yeah, that’s a great question. And certainly, initially, a lot of the reports that we were getting were fairly sporadic. They were low numbers. There was a case here and a case there, and the major difference and the major changes happened leading to that declaration, has primarily been out of the United States, where there is a lot of travel coming back from South America. And the United States itself, at least for the time being, is a non-endemic; there’s no transmission that’s occurring inside the United States through mosquitoes. And we had lots of travelers coming in and the CDC was very aggressively looking for potential cases of sexual transmission, and essentially reported an explosive increase (and I use explosive in a fairly relative fashion), but a large number of women that had acquired the infection from symptomatic men that were noted. So it very quickly, within the matter of a week or two, went from “These are happening fairly sporadically (yes, it’s a mechanism of transmission but it’s not a dominant mechanism of transmission), we’re still focusing entirely on mosquito control and mosquito prevention,” to “This transmission (the sexual transmission) is clearly occurring more commonly than we suspected.”

Now, putting a number on that ‘more commonly’ is much more challenging, and trying to figure out, “If you’re symptomatic, do you transmit it to your partner 100 per cent of the time for each active intercourse, or is it 50 per cent, or 10 per cent?” That’s very challenging to tease out. And it will eventually come out but, for the time being, we have to assume that there’s a fairly high probability of transmission to a sexual partner in the case of a symptomatic man to a woman.

Again, there are a lot of questions we don’t have answers to. For example, if there’s a symptomatic woman, what is the chance of transmitting it to a man? And, of course, there’s much less relevance to that in terms of the risk of a woman getting the infection and potentially infecting a fœtus. And, of course, if a woman is sexually active there’s always the chance that they become pregnant, so the risk is much greater there. So there’s little interest in trying to figure out what the transmission from woman to man is, but it’s still an unanswered question. And the biggest unanswered question is whether or not a man can transmit it to a woman when they are asymptomatic. And of course, there’s studies that are being pursued with that, trying to detect the virus in prostatic secretions or semen of men that are returning from travel that don’t have symptoms but have documented infection.

Harp: Alright, doctor, we’ll leave it there. Thanks again for joining us here on the Infectious Questions podcast.

Lagacé-Wiens: My pleasure.

Balakumar: That was Dr. Philippe Lagacé-Wiens, an assistant professor of Medical Microbiology and Infectious Disease at the University of Manitoba, and a consultant to the Travel and Tropical Medicine Clinic of the Winnipeg Regional Health Authority. Do you have a public health question about Zika virus you’d like addressed? Please email it to

Harp: Infectious Questions is produced by the National Collaborating Centre for Infectious Diseases. Production of this podcast has been made possible through a financial contribution from the Public Health Agency of Canada.

Balakumar: Note that the views expressed here do not necessarily represent those of the Agency.

NCCID’s host organization is the University of Manitoba. Learn more at


A public health podcast produced by NCCID, Infectious Questions connects those with infectious disease questions to those who have answers. Subscribe on iTunes, Stitcher and SoundCloud.