Friday, 5 July 2019

Could our changing lifestyles and a changing climate spell a return of deadly diseases like malaria to Canada? A recent scientific study warns - it's possible!


by Larry Powell
A malaria mosquito, Anopheles albimanus.
Photo by CDC.
Mosquito-born diseases (MBDs) like dengue fever and malaria aren't currently established in Canada, partly due to our harsh climate. But global warming combined with increasing international travel, could change all that. 

New research by a Canadian team from the National Microbiology Lab, the Public Health Agency  of Canada (PHA) and two universities finds, given "an evolving situation" due to climate change, mosquitoes native to Canada "may become infected with new pathogens and move into new regions within Canada." But exotic species may move in, too, bringing diseases like malaria and dengue fever along with them, from afar, as well. 

And, "With high levels of international travel, including to locations where the diseases are present," states the report, "there will be more travel-acquired cases of MBDs."

As a result, the team stresses a need for active surveillance, a high level of awareness and mosquito-bite prevention to guard against a worst-case scenario.
Victoria Ng, PhD
Senior Scientific Evaluator, 
Infectious Disease Prevention & Control Branch
Public Health Agency of Canada / 
Government of Canada

A spokesperson for the study, Dr. Victoria Ng of the PHA (r), tells PinP in an e-mail, "I think one of the biggest impacts of climate change for exotic MBDs in Canada will be the increase in travel-acquired cases as well as the potential for limited autochthonous (local) transmission of diseases where there is climatic suitability for mosquito vectors and reservoirs." 


But these latest findings are not universally-accepted.  An expert who has contributed to other studies of malaria in Canada, Lea Berrang Ford (formerly with McGill University - now with the University of Leeds), is not too concerned. In an e-mail to PinP, Prof. Berrang Ford concedes, climate change could create more favourable conditions for the disease. But he beleieves there are factors other than temperature, such as a strong health care system that'll make a resurgence unlikely.

Dr. Ng agrees, other factors may make exotic diseases born by mosquitoes unlikely in Canada. But, she adds, "There's always the chance that, given a combination of suitable conditions occurring concurrently over time and space, that establishment could occur." She cites the introduction of West Nile virus in Canada some 20 years ago as a case in point. 

While Canada is considered, for all intents and purposes, malaria-free, readers might be surprised to learn, this has not always been the case. It ravaged the early European settlements of Niagara-on-the-Lake and Kingston. While rarely fatal, it also affected those working on the Rideau Canal in the 1830s to such a degree, construction was seriously impacted. Known then as "fever and ague," it was so widespread from 1780 to 1840,  few were spared.

Malaria - a grim reaper

Malaria is one of the deadliest diseases in human history. But, in the past couple of decades, gains in the fight against it have been so significant that. Collectively, they've been called "one of the biggest public health successes of the 21st century."   

However, the most recent figures from an international partnership, "The Global Fund (TGF)," suggest, there's still a long way to go. In 2017, malaria still sickened more than 200 million and claimed the lives of almost half-a-million more, mostly in sub-Saharan Africa. 

And TGF, which allocates public and private funds to combat the disease, believes it's still not certain what the future holds. In some of the almost 100 countries currently reporting the disease, "progress is being made towards its elimination." Others with a higher burden, are still "suffering setbacks in their response." And even more money, beyond the substantial amounts already spent, will be needed, just to make sure the gains stay ahead of the setbacks.

Secrets of malaria exposed. New research peels back the layers which mask our understanding of one of the deadliest diseases known to man. 

Findings just published by a research team from the US and UK reveal, parasites that carry malaria, can mature inside their mosquito hosts way faster, at lower temperatures, than earlier thought. 

Lab tests showed (at between 17 and 20 degrees C), it can take as little as 26 days from the time mosquitoes have had an infectious blood meal, to the time the parasites grow and becomes capable of transmitting the disease. For decades, it’s been assumed it would take about twice that long…some 56 days.
A malaria mosquito, the Anopheles stephensi. Source: CDC.

For more than 50 years, medical experts have been relying on a guide known as the Detinova model to try to map the future course of the disease.  But that model did not fully take into account just what implications those cooler temperatures could have. Neither did it fully explore the impacts of routine fluctuations in daytime temperatures, which can also play a role.


"Ring" stage (in blue & pink) of the malaria parasite, 
Plasmodium falciparum in human red blood cells. 
Microscopic image by Eric Hempelmann.
Unlike previous studies, described in this new paper as “poorly-controlled,” two major malaria mosquito species were tested this time (including Anopheles_stephensi, above). 
“These novel results challenge one of the longest-standing models in malaria biology," states the study, "and have potentially important implications for understanding the impacts of future climate change."
Study co-author Jessica Waite, Ph.D. 
Center for Infectious Disease Dynamics
The Pennsylvania State University.
The study's co-author, Dr. Jessica Waite, tells PinP, "What we hope is that our work will help make better predictions about where, when and possibly how much malaria to expect. We believe our work provides a much-improved estimate for models of malaria." She also believes it'll help governments better direct their financial resources to aid areas that  need it most.

Her team consisted of experts from the Universities of Pennsylvania State in the US and Exeter in England. It acknowledges, there's still a need for further lab and field tests.

The findings have just been published in the journal, Biology Letters by The Royal Society.


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