Canadian mosquito spread of Zika untested

The types of mosquito transmitting the Zika virus in South and Central America can't survive Canadian winters. But what about home grown bugs?

We do not know whether our species can transmit because the studies haven't been done

Zika virus mosquito threat

8 years ago
Duration 1:59
A group of Canadian researchers is examining if it is possible for home-grown mosquitoes to spread the disease

The question of whether our home-grown mosquitoes could spread the Zika virus is one that an Ontario researcher aims to answer.

The dreaded Aedes aaegypti mosquito is the main carrier of the Zika virus. The mosquito species transmitting Zika virus to people in South and Central America can't survive Canadian winters. What about the mosquitoes who already live here? Could they carry the Zika virus?

"I would love to say that our normal Canadian mosquitos can't carry the viruses but honestly we just don't know," said Fiona Hunter, an entomologist at Brock University in St. Catharines.

Hunter is interested in the role insects play in the spread of disease. She's applied to the federal government to study Zika virus at a Level 3 lab. 

In this abridged transcript, CBC's Kelly Crowe asks Hunter about two invasive mosquito species that have become established in Canada and the other known carrier of Zika, the Asian tiger mosquito, that could eventually colonize this country.

Tell us about the mosquito we know carries the Zika virus?

Everybody is talking about Aedes aaegypti as being a major vector for this Zika virus and certainly that's the case down in South America and especially in Brazil [where] they know that Aedes aaegypti has been testing positive for the Zika virus. The other thing about that is that their number of Aedes aaegypti has really gone through the roof. So not only do they have them testing positive, but we also know that the population of Aedes aaegypti has gone up. 

Why has it gone up?

Aedes aegypti is an invasive species and it should actually be in Africa and so it's invasive into the Americas including South America. And so often what happens is a new species gets into a place where it's not supposed to be, it doesn't have natural competitors or natural predators and it does really really well and so the numbers go way up.

We keep reporting that Canadian mosquitoes aren't likely to be a concern.

We don't actually have Aedes aegypti here in Canada. It is in the southern States, it's made of good incursion in southern states but not here. It overwinters in the egg stage, and our climate is just too cold, so they die out. 

However there is a second species we are concerned about. It's the one called Aedes albopictus, which is the Asian tiger mosquito. It is also an invasive species, also found in the southern States, and it's moving its way northwards. In fact, this is one of the mosquitoes that's being transported all over the world and becoming an invasive species everywhere it's going, and it can tolerate cooler temperatures. So the concern is that it may in the future be able to establish in Canada.

It's in southern New York state, in New Jersey, Pennsylvania. It's definitely moving northwards, and we can potentially have it here in the future.

We don't have it now is what you're saying?

We don't have it today. About 15 years ago, when we started our surveillance for West Nile, we found two specimens in the light trap here in Niagara, and we sent them off to export down to Florida who verified for us that they were indeed Aedes abodipitus even though they were not supposed to be here. And that raised all sort of alarm bells, and we have been looking for them ever since and have never found any additional specimens. So we think that back in 2002, they just blew up in wind currents from somewhere in the States but they certainly haven't establish yet a breeding population here.

Why would we be worried about this besides the obvious not wanting to have invasive species here?

We would worry about Aedes albopictus because it's also a potential vector of many Arboviruses, and it is probably a competent factor of Zika virus. Therefore, well we don't have to worry about Aedes aaegypti that's making all the news, we will in the future have to worry about other invasive, such as Aedes albopictus.

While we're on the subject, is climate change and warmer climate the reason why they're moving?

We've got very good evidence that over the past two decades we've had new species coming into southern Canada, and they are range expansions from the south, so for really invasive species, they end up in southern states and move their way up gradually year by year. We had another invasive species coming to Canada, we first detected in 2004, only a few specimens and now it is all over Canada. So it's a sort of things that global climate change, range expansions occurred, and we do get species moving northward.

Can we get into the specifics now about why our homegrown mosquitoes can't carry these viruses?

I would love to be able to say that our normal Canadian mosquitoes can't carry the virus but honestly we just don't know. There have been no transmissions studies done in Canada yet to see whether or not Zika virus can be transmitted by local mosquitoes. We know that we do have several species that we're concerned about and the Public Health Agency of Canada is planning on testing those species to see if they are competent vectors. And here at Brock we also have a containment level three lab where we can also test species. We're just waiting to get the permits to be allowed to work with Zika.

We're actually not accurate when we say with confidence that these Canadian mosquitoes can't carry it. Is that right?

That is actually a true statement. We do not know whether our species can transmit or not because the studies just haven't been done. 

 The species that are in the genus Culex are able to transmit many arboviruses that are related, actually, to Zika virus. However, they have a different life cycle. Culex mosquitoes generally transmit viruses that have a bird as an intermediate host. The thing with Zika virus and also, incidentally with dengue and chikungunya, those are diseases or viruses that can be transmitted from a human to a mosquito to a human, so there's no need for an intermediate host. 

 West Nile seems to ebb and flow so that we had a huge outbreak in 2002 in Ontario and then we had another outbreak out in the Prairie provinces a couple years later. And Ontario didn't have another big surge until 2012, but by then it was old news and really didn't get any airplay. But we're still following West Nile because it has bad years and good years.

What studies do you want to do and what questions you want to answer in terms of the ability of certain species to carry Zika in Canada?

We would want to know whether or not species that are actually found here are capable of picking up the virus and then replicating it inside their bodies and have that virus move to their salivary glands so that when they then feed on their next host, they can spit it into their next host. So, it's called a competency study to look at whether or not our home-grown mosquitoes can transmit.

How and when would you do that study?

We're currently able to work on West Nile in our containment level three lab. We're putting in the paper work to be permitted to work on Zika virus. It would be in a secure containment lab where the general public can't get access to it and then the mosquitoes in there can't actually get out. It's got many barricades to keep everything contained. We would then take mosquitoes that we collect from the wild, bring them into the lab, take them into the containment lab, and feed them blood meals that have the Zika virus in them.

We would need to grow up the Zika virus in cell culture and then lace artificial blood meals with it, feed them to the mosquitoes and then test at different times after feeding whether or not those mosquitoes are infected. And if they're infected, you wait a few more days to see whether or not that virus turns up in the salivary glands and are they able to spit it out. We have ways of actually restraining mosquitoes and putting a little capillary tube over the mouth parts and collecting their saliva, testing that to see whether or not it has the virus in it.

Where are you with that approval?

We have just initiated this, but, because the Public Health Agency of Canada is the one who will do the approving and they're also very concerned about getting the research done, we're pretty confident that the approval won't take very long.

Is there a reason to think that we would be at risk of having dengue and chikungunya spread the same way? 

There's definitely the same risk for dengue and chikungunya. If you look at something like chikungunya, there's been homegrown chikungunya outbreaks in Italy because somebody has come back to the country with an infection, they've been bitten by homegrown mosquitoes, and then it gets transmitted to other people. All of these vector-borne diseases, we're really having to check them out more carefully.