IQ1: Zika Virus and pregnant travellers

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Rick Harp: Welcome to Infectious Questions, a brand new podcast produced by the National Collaborating Centre for Infectious Diseases. At NCCID we work to help public health practitioners find, understand, and use infectious disease research and evidence. And one way we do just that is this very podcast.

Hello, I’m Rick Harp.

Shivoan Balakumar: And I’m Shivoan Balakumar.

Now, for this first run of episodes, we will be focusing on an emerging infection very prominent in the media right now: Zika virus. We know it’s prompted many questions across Canada among public health professionals and those that they serve.

Harp: And that’s what this program is all about, helping those with infectious disease questions connect to those with the answers. Speaking of which, let’s introduce you to our first guest, Dr. Philippe Lagacé-Wiens, an assistant professor of Medical Microbiology and Infectious Diseases at the University of Manitoba, is also consultant to the Travel and Tropical Medicine Clinic of the Winnipeg Regional Health Authority.

Doctor, welcome to Infectious Questions.

Dr. Philippe Lagacé-Wiens: Hi.

Harp: Now, I understand a common question you’ve heard, both by way of patients and practitioners, goes something like this: “I’m going to Mexico soon. Should I cancel my trip because of the Zika virus?” And I know that this question comes from both pregnant women and their partners. How might public health practitioners respond to that question?

Lagacé-Wiens: That’s a very good question because it does really represent the type of thing that we are getting from the field, and I often like answering these questions by delving into what the risks are and the people’s perceptions of the risk. And often, you have to let individuals make their own decisions once they fully understand it.

So, to put things in perspective with the Zika virus specifically, the data that we are getting coming out of South America, and in particular, Brazil—where the epicenter of activity is, and where they’re getting the most cases—would seem to suggest if you live there for one month, your chances are approximately one in a thousand of getting Zika virus infection. And although we don’t have good data from other parts of the Americas, you can probably assume that rates are somewhat lower as you go into Mexico and the Caribbean. But, as a starting point, we can think of it that way.

And putting that into a little bit of a perspective, if you’re going for a couple of weeks, your risk is then 1 in 2,000, or even 1 in 4,000, of being infected with this particular virus. And if you compound that with the risk of the average person, of getting not only infected with the virus but actually getting ill from the virus—which is only about 20 per cent, as 80 per cent of people will be asymptomatic when they get this infection—the risk really starts to be negligible.

And I think ‘negligible’ is an excellent way to describe that. For the average Canadian traveling to these destinations, the risk is negligible of any severe outcomes from Zika virus.

Now, you’ve thrown in the pregnancy question. And a pregnant woman, a woman who’s intending to be pregnant, falls into a very special category. Given the evidence that we’re seeing, a link between bad fetal outcomes or congenital infections leading to bad outcomes in the fœtus and infection during pregnancy. Now, with regards to that, again, data is starting to come out, is still very limited, but we’re seeing from the best quality data that somewhere between 1 in 4 and 1 in 3 women who are pregnant and have a symptomatic infection with this virus, that there could be a bad fetal outcome. So, some congenital abnormalities related to that infection. Again, it’s not proven that the link is there, but this is by far the strongest evidence that we have so far.

So if you take this whole picture into consideration, you can often get to explain to patients what the overall risk of infection is, and if you’re pregnant, what the overall risk of a poor outcome (should you get infected) is. And with that sort of information, I think women who are pregnant can make an educated decision as to how they feel they perceive that risk. And again, travelers who aren’t pregnant, which fall into a category that is of negligible risk, can also make an educated decision.

Harp: Now, when it comes to pregnancy and Zika, I know that we’re learning more and more literally every week, every day, but what do we know now about the level of risk depending on what trimester a woman is in when she travels to an affected area?

Lagacé-Wiens: Yeah, and that’s another great question. To be sure, a week or two ago, many people would have been saying that the earlier the infection, the higher the risk of a very poor outcome. So if it was in the first trimester, it would be the highest risk; second trimester, an intermediate risk; and third trimester, the lowest risk. And that would follow the pattern of what we see with a number of other types of infections that can lead to the same outcomes.

That being said, with recent evidence that’s now coming out of Brazil—and this is very hot off the press—we’re seeing that there are a number of women who are in their late pregnancies that are being described as having some congenital abnormalities presumed to be from the infection. And so I think, at this point, we have to say that we don’t have a solid answer to that. The evidence would point towards there could be bad outcomes in any trimester, and I think that’s probably the best that we could say for now.

Harp: Now, one thing that might be of help here is to put Zika-related risks into perspective by comparing it to other risks to health. Can you do that for us?

Lagacé-Wiens: Good. I like to answer that question because it does help provide some perspective.

And I like to use other travel-related potential risks. And one of the common ones that people will hear about when they travel is malaria, as a good example. And if you think about malaria, and if you go to an area of the world that has a very intense transmission of malaria (so, say Sub-Saharan Africa, and we have lots of travelers who are going there)—so I’m trying to compare intense malaria transmission with intense Zika transmission—and your risk of acquiring malaria in a country with high-level transmission is really about 20 times higher than your risk of getting Zika virus.

Likewise, if we think about dengue virus—which is, interestingly, a virus in the same group as Zika virus and it’s transmitted by exactly the same mosquito in Brazil. (And, interestingly, Brazil, in the past year has seen a dramatic increase in dengue infections, and then they’ve basically called a very serious dengue outbreak, which has kind of gone into the shadows now with this sort of Zika outbreak, but it’s certainly been in the back of my mind.) And so, your risk of dengue in Brazil is approximately the same as Zika virus.

So, I was throwing numbers like one in a thousand for a month, and that’s probably about the same as it is for dengue, although it’s difficult to get accurate data. But the difference between dengue and Zika viruses—for the average traveler, dengue virus can be very serious. It can be deadly, in fact, and even with the best of care somewhere within the realm of 2 to 3 per cent of people will die if they get dengue infection. So when you put that into perspective with an infection where you have 80 per cent of people who have no symptoms at all and the other 20 per cent will get very mild symptoms (maybe feel like they’ve got a flu and will resolve within five to seven days), you really start to see relative risks here.

And when you think about the pregnancy, it certainly adds an element of risk and a lot of pregnant women are very, very risk averse for obviously good reasons, and so they will often perceive that risk as being sufficient not to travel.

Harp: Dr. Lagacé-Wiens, thank you very much.

Lagacé-Wiens: My pleasure.

Balakumar: That was Dr. Philippe Lagacé-Wiens, an assistant professor of Medical Microbiology and Infectious Diseases 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 the Zika virus you’d like addressed? Please email it to nccid@umanitoba.ca.

Harp: Thus concludes this inaugural edition of Infectious Questions, 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. The host organization of the NCCID is the University of Manitoba. Learn more at nccid.ca.