03/17/2016 09:48 EDT | Updated 03/18/2017 05:12 EDT

Risk Of A Canadian Zika Epidemic Is Small But Very Real

Mosquito (Theobaldia annulata) sucking blood.
Photographed and edited by Janos Csongor Kerekes via Getty Images
Mosquito (Theobaldia annulata) sucking blood.

As of March 14, 25 cases of Zika have been reported in Canada. But these have all been travel-related. They are imports. Canadians have travelled somewhere else in the world, somewhere warmer, gotten infected, then been diagnosed upon their return to Canada.

So far, no case of Zika has been contracted in Canada. But some people wonder if that might change.

At first blush, this question seemed silly, especially when asked in the middle of a cold Canadian winter. But winter is receding and some people in Hamilton who know what they are talking about are asking that very question.

Could Zika come to Canada?

Tropical diseases are "tropical" because they spread only or primarily in the tropics. But we do not know to what extent this is due to how the virus is affected by climate or how the host (the mosquito, in this case) is affected by climate.

For now, the best thing is not to panic. We are learning about Zika, and part of that learning has to focus on protecting Canadians.

There are 3,549 known species of mosquitoes. The one that typically carries the Zika virus is Aedes aegypti. Its range is in the tropics, so it does not wander north to Canada. Nothing to worry about, right?


Although at this point the chances of a Zika epidemic in Canada seem remote, there are six reasons why we need to remain vigilant.

Canadian mosquitoes could bite infected travellers.

Imagine this scenario: a Canadian gets infected with Zika in Mexico or the Caribbean. He returns to Canada, where he is bitten by a few Canadian mosquitoes. Those mosquitoes are now infected. Each of those mosquitoes goes on to bite several other people, infecting them with the virus.

Fact or fantasy? The truth is, we do not know. That's why the scientists in Hamilton are testing Canadian mosquitoes to determine if they could become carriers.

The range of Aedes aegypti could broaden.

Although the current range of Aedes aegypti is contained to the tropics, it has plenty of room to spread further north within "predicted habitats." Florida and Texas are highly suitable, and much of the southern U.S. is moderately suitable.

A broader range would bring Zika closer to Canada and more Canadian travellers would be visiting Zika zones.

Aedes albopictus is even closer.

There is a second species of mosquito that is known to carry Zika: Aedes albopictus. Predicted habitats for this species include most of the eastern United States right up to Connecticut and Massachusetts. That could put Zika in our backyard and expose many more Canadian travellers to the virus.

Other species could also be infected and pass on Zika to humans.

Another species has been identified as a potential carrier: Culex quinquefasciatus. This species is 20 times more common than Aedes aegypti. At this time, we know that this species can be infected, but we have no idea if it can transmit the infection to humans.

With 3,549 species to test, now might be a good time to direct your children to a career in micro-biology.

The virus might adapt.

In the movie Jurassic Park, Ian Malcolm famously said that "Life will find a way." Viruses seek to spread, and they often mutate very quickly to do so.

If the virus recognizes the benefits of making itself adaptable to a variety of similar hosts, who knows how many mosquito species it could infect?

If the virus recognizes the benefits of making itself adaptable to a variety of climates, who knows how far north and south it could spread?

In his thriller novel The Third Pandemic, Pierre Ouellette tells of how two viruses meet up inside a bird in a remote corner of Africa, mutate and become deadly, before spreading through air travel to all corners of the world. In fiction, the author always creates the perfect storm; in the real world, it could happen, too.

Mosquitoes might adapt.

It's hard to imagine Aedes aegypti in the streets of Montreal. But no harder than imagining bananas, pineapples and mangoes on sale at the Atwater Market -- in winter! In fact, Aedes aegypti has been found in Washington, DC, having wintered in sewers.

Mosquitoes are on the move, expanding their territories and hopping continents. Thanks to increased human travel and goods shipments around the world, mankind is spreading mosquitoes everywhere. When they can survive a change of climate or adapt to a new climate, they bring the risk of new diseases with them.

The worry is that diseases like Zika, Yellow Fever, Dengue and Chikungunya could spread with their hosts to previously safe areas, such as Canada.

The climate might adapt.

If the mosquitoes and the Zika don't adapt, Canada's climate might adapt. If climate change raises Canada's temperature by a couple degrees, we open the doors to all sorts of new invasive life forms.

Predicting the future is always hard. But it is even harder when you don't know the present. Zika has flown under the radar for some time, and the truth is that there is so much about it that we just do not know. Much as nobody wants to hear this, we will have to be patient a little while longer.

For now, the best thing is not to panic. We are learning about Zika, and part of that learning has to focus on protecting Canadians in the event that any of the scenarios above begins to look probable.

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