IQ3: Birth defects and the Zika Virus


This episode continues our focus on Zika virus. Here, our guest expert addresses the strength of the link between Zika infection and birth defects like microcephaly.

APRIL 2016 | apx. 9 min.

IQ3: Birth defects and the 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. So far in our series, we’ve looked at the risks the virus poses to pregnant travelers and the likelihood of sexually transmitting Zika. This week, we address the strength of the link between Zika infection and birth defects like microcephaly.

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: So this week, we’re gonna deal with a question that never seems to go away. I understand that you’ve been approached with this, and it kind of more or less takes the form of this: “I’ve heard in the media that it’s not Zika virus that’s leading to microcephaly, it is a pesticide that has been used to kill the mosquitoes that has generated these kinds of congenital birth defects.”

What’s your response to that?

Lagacé-Wiens: So, that is a good question, and certainly, when this epidemic of microcephaly and other neurological disorders was initially reported, people sought explanations besides the Zika virus, as that was the one that was initially presented as the probable cause. And I think that’s actually healthy skepticism, in order to spur scientific inquiry and to try to look at alternative explanations for this. And they have, certainly; pesticides and heavy metals and nutrition or poor nutrition, have all been quoted as possible relationships with this epidemic of microcephaly, but I think for the large part, at this point, are detracting from the actual cause, which is almost certainly the congenital infection with the Zika virus.

And the reason I say that is a lot… the most recent evidence coming out of case control studies in Brazil, which have looked at women from a variety of areas that are pregnant, that has been infected with Zika virus, have also looked at groups of women from a variety of socio-economic classes to try to assist in teasing out whether this is a Zika effect or socio-economic or regional factors, have demonstrated that congenital defects will happen in all groups regardless of their socio-economic status, or the region of the country that they come from, or whether they come from slums versus more affluent areas. So that certainly points against there being alternate environmental factors.


The other thing, of course, is that most of these pesticides have been used for decades and no such link has been observed. Until then, they have been used in other countries as well. A lot of them have been studied quite extensively and not found to have these associated links, which adds support to the argument that this is Zika virus. And additionally, nutrition factors and heavy metals have also been present for a long time before the epidemic has been described.

That’s not to say that some factors can’t be additive. In other words, poor nutrition, folate deficiencies, can be associated with neural defects and brain abnormalities. And having a Zika virus infection on top of that may be additive in its effects, however, the large proportion of this, these abnormalities can probably be attributed to infection.

The other thing that a lot of people have asked is, we have Colombia that’s right next door, not yet reporting any cases of microcephaly that they deem to be associated with Zika virus infection. And certainly, this is ongoing surveillance, so we may see in the next week or two, or month or so, that there’s more evidence to suggest that there is a link. And we can’t discount the possibility that there’s been changes or mutations in the virus that leads to high risk of congenital infections in the Brazil variant, if there is such a thing, a variant in Brazil, compared to the Colombian variant, because these are viruses that are known to mutate quite readily, quite quickly, and can adopt new properties very rapidly and a higher probability of congenital infection could certainly be one of those viral properties that has changed over time.

Harp: Dr. Philippe Lagacé-Wiens, I think it was Mark Twain who said, ‘A lie can spread halfway around the world before the truth has even got its pants on in the morning’. Why do you think these kinds of speculations and rumours persist despite evidence seeming to be pretty strong that there is no link between the pesticide and microcephaly and Zika?

Lagacé-Wiens: Well, I think humans in general like to be able to explain things through things that they actually have control over as opposed to things that they cannot control. So I think it gives people solace to think that ‘there’s a risk but it’s modifiable; I can alter my behaviours and reduce that risk’. And it gives comfort to people.

So I think that there’s a natural inclination to believe these things, whereas, if you’re dealing with a mosquito-borne virus, although there are modifiable factors, you can’t bring the risk down to zero. And I think that scares people, so they try to find alternative explanations to justify their actions, you know, ‘I still really want to travel’, so, maybe I can justify that by saying, ‘Well, I have to avoid the pesticides’, and, ‘I’m not gonna go into those areas’, and, ‘I’m not gonna drink the water’. And things like that.

In the end, the biggest piece of advice that I can give is that there are modifiable risks that you can have even with mosquito-borne illnesses, and you know, wearing your repellents, wearing light-coloured clothing, loose-fitting clothing. In the case of this virus, bed nets when you’re napping in the daytime, in the case of other diseases, bed nets when you’re napping or sleeping at night. So it’s… these are all good things in the end, and I think if we all adopt those behaviours we’ll be better for it. But as I say, I think a lot of people try to give themselves solace by believing these things that are perhaps more easily avoidable.

Harp: Dr. Lagacé-Wiens, thanks again!

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.