Once bitten, twice shy: Malaria in Canada

Karen Cholmondeley
26 March 2014

Above: "Brewer's Lower Mill; View down the Cataraqui Creek, & and Clearing made for the Canal. Excavation for the Lock just commenced, 1829," Watercolour, Thomas Burrowes fonds, Reference Code: C 1-0-0-0-67, Archives of Ontario, I0002186

Fast Fact: Chloroquine used to be the most popular and cheapest form of malaria treatment. However, Plasmodium falciparum, the most deadly malaria parasite, has evolved to become resistant to this anti-malaria drug.If you have ever been camping, you know the importance of bug spray. Back in the 1800s, there was no such thing as bug spray available to protect against mosquitoes carrying the malaria-causing Plasmodium parasite. Back then, malaria used to kill hundreds of people in Canada each year! However, by the mid-1900s, the disease had been completely eradicated (wiped out) across the country. How was this achieved? And could the disease return?

While there were malaria outbreaks in various parts of Canada in the 1800s, one of the hardest-hit regions was Southeastern Ontario, where the Rideau Canal linking Ottawa and Kingston was built between 1827 and 1832. Construction workers were toiled in swamps, the perfect breeding and feeding ground for mosquitoes, during the summer. And workers and their families lived in construction camps along the unfinished canal, providing a large human population for mosquitoes to feed on.

Malaria transmission. Click image to enlarge. (Karen Cholmodeley)

Even if only a few mosquitoes carried the malaria-causing Plasmodium parasite in the beginning, after one person was bit and infected, the parasite was available in that person’s blood for other mosquitoes to ingest (STEP 1 in the image on the left). As more and more mosquitoes bit the infected person, more and more of them became carriers of the parasite (STEP 2). Finally, these newly-infected mosquitoes bit more uninfected people, giving them the parasite and causing them to contract malaria (STEP 3).

This cycle of infection continued until malaria ran rampant along the Rideau Canal. According to construction records, up to 60% of workers in the region became ill. As many as 500 people died from malaria during the construction of the canal, including workers, members of their families, and nearby residents.

Slowly, the cycle of infection was broken. One of Canada’s greatest defences against malaria was (and is) its climate. Each winter, most mosquitoes die off from the cold, disrupting the transmission of the parasite. By the 1900s, people were living in houses with better windows and insect screens, reducing the number of bites. In addition, increased land development destroyed a lot of mosquito habitat, resulting in fewer mosquitoes overall. Finally, the highly effective anti-malaria drug quinine became widely available. This drug quickly kills the parasite in humans, reducing the chances of malaria being transmitted to others.

Fast Fact: People travelling to countries where malaria is widespread can take a variety of highly-effective anti-malarial drugs before, during, and after their trip to prevent infection.Despite Canada’s past success in eradicating malaria, there are concerns that the disease could become established in the country once again. In fact, several hundred cases of malaria are diagnosed in Canada each year. Currently, however, these cases are limited to people who became infected in another country. Nevertheless, milder winters increase the chance that sufficient numbers of parasite-carrying mosquitoes could survive long enough to keep the cycle going.

What’s more, because malaria is rare in Canada, it is not readily recognized by doctors, causing delays in treatment. The longer an infected person goes without parasite-destroying treatment, the more opportunity there is for another mosquito to bite them and start the cycle anew.

Canadians are very fortunate that their climate, standard of living, and medical resources have allowed them to eradicate malaria, but the disease is still out there. Until malaria is eradicated worldwide, there is always a chance that the Plasmodium parasite could re-establish itself in Canada if given the right conditions. Malaria was a devastating disease for workers on the Rideau Canal, as well as other Canadians in centuries past. In the years to come, continuous monitoring will be crucial to ensuring present-day Canadians avoid a similar fate.


General information

Brief Overview of Malaria in Canada: From Past Elimination Efforts to Future Risk Factors (Kelly Kavanagh Salmond, Canadian Public Health Association) Choosing a Drug to Prevent Malaria (US Centers for Disease Control and Prevention) History of Malaria, an Ancient Disease (US Centers for Disease Control and Prevention) History of the Rideau Canal (Ken Watson, Rideau Canal World Heritage Site) Malaria – A Rideau Mythconception (Ken Watson, Rideau Canal World Heritage Site)

Scholarly publications

Berrang-Ford L, Maclean JD, Gyorkos TW, Ford JD, Ogden NH. 2009. Climate change and malaria in Canada: a systems approach. Interdisciplinary Perspectives on Infectious Diseases. 2009:385487. Kokwaro G. 2009. Ongoing challenges in the management of malaria. Malaria Journal. 8 Suppl 1:S2. MacLean JD, Ward BJ. 1999. The return of swamp fever: malaria in Canadians. Canadian Medical Association Journal. 160(2):211-212.

Karen Cholmondeley

I recently completed my MSc. and am now actively seeking my next adventure! I love science because it helps offer explanations to so many different questions affecting all aspects of our lives, from health to nature to technology. In my free time I love to read, travel, and be outside (unless it's cold!).

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