The global implications of Zika: 10 questions for infectious disease expert Kamran Khan

Toronto-based Khan discusses next steps following the WHO's emergency declaration, whether the virus could eventually head north and lessons from the Ebola outbreak.

By: /
February 5, 2016
A health worker fumigates the cemetery of Surco to prevent Zika virus and other mosquito-borne diseases in Lima, Peru February 5, 2016. REUTERS/Mariana Bazo

On Feb. 1, the World Health Organization (WHO) declared mosquito-transmitted Zika virus to be a public health emergency, following a massive outbreak in Brazil and the virus’ subsequent spread to at least 25 countries in the Americas. Zika has been linked to thousands of birth defects in Brazil, and Latin American governments have taken to warning women against getting pregnant until 2018 – a recommendation with significant social impacts in countries where birth control and abortion may not be readily available.

Dr. Kamran Khan is an infectious disease physician with St. Michael’s Hospital in Toronto. He is also the founder of BlueDot, which develops web and mobile technologies to help policymakers prepare for and respond to infectious diseases.

OpenCanada spoke with Dr. Khan about the implications of the WHO’s emergency declaration and the ‘known unknowns’ in the international response to Zika.

1. What are the implications of the WHO declaring Zika an international emergency?

In some ways, [this declaration] is a kind of international S.O.S., alerting countries around the world that this is a significant threat, and that it’s going to require an internationally coordinated response which the WHO will lead. It results in priority setting around key areas of research, which might for example be around diagnostics, or may have to do with vaccine development, some may have to do with mosquito control measures. The purpose is also to help mobilize resources, to respond to the epidemic in a vigorous way. 

2. What considerations go into this kind of decision?

The International Health Regulations (IHR) are basically the global playbook for how to prepare for and respond to these types of global epidemic emergencies. One of the key tenets of the IHR is to find a balance between the public health response to these types of events and avoiding what they call unnecessary disruption to international travel and trade. 

The reason being – and this is I think one of the reasons we didn’t hear more about travel advisories – is that if countries feel a very strong economic disincentive to reporting cases, because they feel that immediately they will have some economic consequences through a travel restriction or advisory, they may be more disinclined to share that type of information. If [countries] happen to be a little more reserved in sharing information comprehensively and in a timely way, then the whole world loses in that situation.

3. What was it about Zika specifically that contributed to the decision to make an emergency declaration?

With these types of emergencies, there’s an Emergency Committee, so they’re going to weigh all of the evidence. Some of the key factors will be: the scale of the epidemic, and in this case we’re now looking at estimates of somewhere between one and two million cases, and over 25 countries I think now are reporting cases; the rapidity with which the epidemic is spreading; are there countermeasures like antiviral therapy or a vaccine; and what are the consequences of the infection.

So in this case, this issue of microcephaly is the big one. I think what probably was a key factor in determining whether or not to declare a public health emergency of international concern was how the committee weighed the evidence on the association between Zika virus infection and microcephaly, and clearly they must’ve felt strong enough that the evidence was strong. It may not be 100 percent definitive, but compelling enough to declare this a public health emergency.

There’s also a recognition of the potential for this, in that it does have pandemic potential, meaning that Aedes mosquitos happen to be distributed around many other parts of the world, including many resource-limited countries. [So the committee would be asking] is it possible that this could be introduced into some of those frontiers, and what might happen in those circumstances?

4. What are the most crucial next steps?

Some of the crucial next steps are, first of all, in countries that are affected, whatever measures they can take to control the mosquitos. This is a virus that has its life cycle between humans and mosquitos, and those are really the main places to intervene. So on the human side, we don’t have a vaccine, we don’t have antiviral therapy, we can only influence human behaviour to try and minimize getting bitten by mosquitos, number one.

Second, on the mosquito side, the main issue is going to be eliminating breeding grounds for the mosquitoes, and seeing if there are measures that [countries] can take to kill the mosquitoes themselves through more traditional means. There has been some research on genetically modified mosquitos and their release into the wild; I think those are more longer-term solutions, not something for the short term.

For other countries that are currently unaffected, I think this is where heightened surveillance in key areas that are vulnerable becomes extremely important – knowing the places where a local transmission of Zika is possible, and where might it be introduced, and then subsequently trying to take measures to first of all educate the public, educate health care providers, and then trying to take as many environmental measures as possible to eliminate the breeding sites for mosquitos. [Countries] may not be able to stop travellers from coming in who may be infected, but if they can minimize the potential for the individuals to infect mosquitos locally and then propagate the cycle in their home country, that is going to be a key activity.

What I’ve described is largely the short-term activities; the longer-term things are going to be more around making sure they’re setting up diagnostics, looking at ways to contribute to vaccine development and so forth.

5. At the moment, mosquitos in Canada aren’t the kinds that would be able to carry Zika – is that likely to change?

I think we’re going to have to wait and see what happens here, but based on the current evidence I don’t think that people should lose sleep over whether we’re going to be seeing outbreaks in Canada. Aedes aegypti is the mosquito that we feel pretty confident is a key vector for Zika virus, and Aedes albopictus is possibly a vector but we don’t know for sure. Neither Aedes aegypti nor Aedes albopictus are found in Canada. Other species of Aedes mosquitos are found in Canada, but right now there is no evidence to suggest that these mosquitoes can transmit Zika, though there is some research being proposed to study this further.

6. This outbreak of Zika began in Brazil, which has reportedly “declared war” on the mosquitos carrying the virus. Do you see a scenario in which Brazil might be forced to cancel this summer’s Olympic Games?

Honestly, I feel like it’s too early [to tell] and I’ll explain why. When you have an epidemic, the fuel for the epidemic are people who are susceptible, who have no immunity to the virus, that’s what basically causes this big explosive epidemic, to use [the WHO’s] Margaret Chan’s words. And what happens in a population, as a disease starts to move through it, is the proportion of the population that is susceptible starts to decrease, and the proportion of the people that are immune starts to increase. And so the fuel starts to decrease and the epidemic doesn’t look quite as explosive; it peaks, [tapers off] and then it starts to decline and become less active.

Between now and August it’s very possible – and the challenge is we don’t really have good studies or modeling of this epidemic, in part because 80 percent of the cases are invisible to us, because they have no symptoms – but it is very possible that this may have cooled off significantly between now and August. We just don’t know, to be honest, and I think it’s premature to say between now, the beginning of February, and August, you know, what will happen.

Brazil is clearly well aware – they’re going to obviously be taking as many measures as possible to try and minimize the breeding sites for the mosquitos, fumigation and so forth, to try and create as safe an event as possible. But I think at this point in time it may just be that the natural cycle of an epidemic brings us to a point where the disease is far less active in August than it is today. 

7. A case of Zika being transmitted through sexual contact was reported in Texas this week – what are the questions surrounding this kind of transmission?

The challenge again is we’re really learning with limited information. There have only been three cases that speak to the possibility of sexual transmission. But I think what we’ve arrived at here is a situation where we can’t ignore sexual transmission anymore, just as an anecdote. While it still probably reflects a small proportion of cases, we still just don’t know the role of sexual transmission and the dynamics of this epidemic. It’s probably overwhelmingly transmitted through mosquito bites but this might be another mode of transmission.

The big question that we don’t have an answer for now is how long does it persist in the semen of individuals, of males who are returning from an area, and if they return with no symptoms, what would be a reasonable amount of time that we would suggest that they use barrier method if they’re sexually active. And if they do have symptoms, well, what do we do in that situation?

8. What do you think of the various recommendations by health departments for women not to get pregnant, is that a short-term solution? What are the social implications in places where birth control or even abortion is not available or, worse, is illegal?

It is a really big social dilemma, because as you mentioned, in some of these countries it’s illegal to terminate a pregnancy. Much of the region is Catholic and some of the countries have policies where that would be considered a crime. There’s no simple answer. On one hand, if children are born with microcephaly, we could have in the future a cohort – I don’t want to say a generation of – but we could have a large number of children who are affected with microcephaly and will need all the appropriate social, educational and health support over their life. [But] for women who would not like to continue with the pregnancy, what are the options that they have available to them?

I think it will be very interesting to see whether or not countries actually relax some of those measures – they do have exceptions, for things like incest, rape, etc. Personally I think it would be very interesting to find out if there’s any direction from the Catholic church or the Vatican, is there anything stated there as to how to we reconcile all these various positions with respect to religion, the law and then the health implications of this particular situation. 

9. What lessons are there to be learned from Ebola and other recent outbreaks?

One of them is, you have to act quickly, and I think we’ve seen the WHO convene the Emergency Committee earlier than they did in the Ebola epidemic, I think that’s a positive sign.

Aside from the immediate response to this epidemic, what I think is the more important lesson is that we retain memory of these events. The world tends to have a way of looking at these events, responding to them urgently, and then, as they diminish, to kind of take our foot off the gas, so to speak, and focus on other things.

If there’s anything we’ve learned over the last 15 years or so, since the SARS epidemic in 2003, is that these events are occurring with greater frequency and with very profound global implications, and it’s very important to make sure we’re putting sufficient energy into addressing the root causes and preparing for and focusing on prevention, just as much or maybe even more so than we’re focusing on the response. This is the whole ‘an ounce of prevention is worth a pound of cure’: we do tend to respond very vigorously when these events happen, but we forget about them fairly quickly after they’re over. 

10. What are you working on now?

We have partnerships with a number of different countries around the globe, in South East Asia, with the U.S., with the European Union, and academic partners at Oxford, Harvard, the University of Washington – some great collaborations that resulted in our paper in The Lancet. We’re continuing to add to that science and trying to build upon it. Ultimately these are very complex problems; government alone can’t solve them, academia alone can’t solve them, and industry alone can’t solve them. We’re using different mechanisms to try and tackle the problem of emerging global diseases like Zika and many others that came before, and inevitably more that we will see in the future.

This interview has been edited for length and clarity.