March 30, 2020

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Scientists put pandemic's potential link to climate change under microscope

Experts studying the effects of climate change on the spread of disease are watching COVID-19 and the response to the pandemic very closely.

"Environmental changes, including climate change, are drivers of the emergence of new diseases," said Nicholas Ogden, director of public health risk sciences at the National Microbiology Laboratory.

He emphasized there is currently no evidence supporting the idea COVID-19 arose as a result of climate change. Much the way it is difficult to pin the cause of any single extreme weather event to climate change, so too is the struggle with the spread of individual diseases and illnesses.

However, the general trend is that more unknown diseases will pop up as the world warms.

In relation to COVID-19 and other new illnesses, this means that while the pathogen existed prior to the infection of a human, a changing environment allows for it to adapt and become more prevalent in the new conditions and, consequently, potentially become more available to jump from animal carriers to people.

"Climatic and other environmental changes, such as loss of biodiversity, can change the environment of pathogens, which mean they evolve, and they may evolve into something which is more infectious to us," Ogden said in a phone interview from Montreal.

"They evolve, just by happenstance, to being more transmittable to humans. And then, as we’ve discovered in our infinitely interconnected world now, once it’s set off, it sets off across the world. COVID-19 is an extremely effective example of that."

But Manitobans need not look far for examples of other diseases that are — and have — spread as a result of climate change. Lyme disease was constrained to one small area of Ontario until the early to mid-2000s when Canada witnessed the proliferation of the black-legged tick across the country, along with the bacteria they carry that causes Lyme disease.

The expansion of the black-legged tick’s range has been linked directly to a warming climate.

Lyme disease is one example of what are known as vector-borne diseases — which are human illnesses transmitted by a living organism either from other humans or from animals. Vectors are often bloodsucking organisms, which also include mosquitoes.

Canada is particularly susceptible to the changes in the spread of vector-borne diseases since it is warming at twice the global rate. This means Canada could possibly become home to ailments that have never existed here before, including exotic mosquito-borne diseases such as dengue fever or the Zika virus.

It’s easier to track how vector-borne diseases are linked to climate change because researchers can track how the vectors — the ticks or mosquitoes, for example — expand in the range hospitable to them as things such as temperature and precipitation change.

Take the Asian tiger mosquito, as an example. It was previously not seen further north than Pennsylvania, but in 2017 was found in southern Ontario by officials in Windsor-Essex County Health Unit. The Asian tiger mosquito is a notorious carrier of Zika, dengue and malaria.

"It’s still at relatively low densities, we think, and it’s unlikely we’ll get sustained transmission, but we can’t rule out the possibility that wherever that mosquito moves in we could have occasional transmission," Ogden said.

Even diseases that spread through food are likely to become more prevalent.

Of course, as with any predictions or forecasting associated with climate change, how significant the impact is depends entirely on how successfully the world manages to lower emissions from greenhouse gases produced by human activity.

Sarah Lawrynuik

Sarah Lawrynuik

Sarah Lawrynuik reports on climate change for the Winnipeg Free Press. Funding for the Free Press climate change reporter comes from the Government of Canada through the Local Journalism Initiative.

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