Lyme marches on

It may not have the global urgency of a pandemic, but public health observers are carefully watching the presence of disease-carrying ticks continue to grow in Canada. Public health authorities are now also anticipating growth in federal funding to continue following this trend. At the forefront of this work is the Canadian Lyme Disease Research Network (CLDRN), which now expects to be supported well beyond its original operating timeline.

“I'm not sure how much I can speak to it,” Dr. Patrick Leighton (PhD), a Université de Montréal professor of veterinary medicine who directs this organization: “But we're looking for additional support to allow us to expand beyond [the original funding.]"

Under its original 2018 mandate, he explained, the CLDRN received $4 million — $1 million per year — over four years with the funding slated to expire this year. But due to the COVID-19 pandemic, the research window was expanded through to 2024. Additional funding is still being negotiated and details are expected to be finalized by year-end 2022, he added.

Dr. Leighton, who specializes in tick and mosquito-borne diseases and has studied Lyme for about 15 years, said this additional funding comes as the tick populations expand in hot spots across Canada. Those regions include Southern Nova Scotia around Lunenberg, the Kingston area of Southern Ontario, southwestern Quebec, and southern Manitoba, where residents are at a higher risk of Lyme disease.

Considered by the drug maker Pfizer to be the most vector-borne illness in the northern hemisphere, Lyme is caused by the Borrelia burgdorferi bacteria transmitted by Ixodes ticks. Depending on when treatment is provided, symptoms range from a small rash and fatigue to headache, mild stiff neck, and heart and nervous-system issues.

Dr. Leighton became CLDRN’s director about six months after previously leading one of its research pillars. He has been part of the network since helping to write its original grant application to the Canadian Institutes of Health Research.

Despite the pandemic “hiccup,” CLDRN members were able to get out in the field and collect new data on ticks across the country. Initial successes have allowed the network to develop 200 field sites in 40 central regions across Canada. Dr. Leighton also points to a major milestone in 2019, which was the establishment of the Canadian Lyme Sentinel Network, the first standardized, pan-Canadian surveillance initiative for the country.

“So we really have a structure now that will allow us really to track the impact of climate change on disease risk for arguably the most important set of climate sensitive diseases that we face as a nation,” he said. “So this is something that we built, has shown extremely high success, and is now really well positioned to provide ongoing, interesting and useful data in the context of climate change.”

Now that effective medication has thwarted the spread of Lyme through dogs and cats, CLDRN researchers are attempting to tackle spread through mice and other rodents — the primary carriers of disease-borne ticks in the wild. This work includes the development of bait boxes containing oral vaccines covered with peanut butter, which can attract the rodents and stop human infection in wild lands, parks, or back yards.

“So that turns the rodents into a little tick-killing machine,” said Dr. Leighton, describing the vaccine’s effect as the animals consume the treated baits. “It kills the ticks that are involved in keeping the cycle [of Lyme disease] in nature going. So we're not going out and spraying chemicals into the environment to kill everything, [which is] obviously not a good idea.”

He added that lab and field testing of this approach has so far proved promising. Meanwhile, work continues on a human equivalent of the vaccines that kill ticks in dogs and cats. Drugmakers Pfizer and Valneva have begun clinical trials on a vaccine involving 6,000 people in the U.S. and Europe. If results are favourable, this product could become the first Lyme vaccine used in North America for 20 years, when a similar vaccine was pulled from drugstore shelves because of insufficient sales.

Leighton described the new vaccine will be a “wonderful development”, if and when it comes to the Canadian market. But he cautioned that it would not address all aspects of the problem, since it will be most relevant to people in high-risk areas.

“For the rest of the population of Canada, with occasional exposures, or [someone] who's travelling to an area with Lyme disease risk for vacation or something, it might not be the number-one solution,” he said. “But, I think, absolutely, whenever it becomes available, it would be a huge help, especially in some of these highly endemic areas like Southern Nova Scotia, and parts of southern Ontario and Quebec, where people are being exposed in their backyards on a daily basis.”

The CDLRN’s efforts include getting Lyme disease patients more involved in research. But despite inroads made in preventing the disease, the number of cases will grow.

“I'd like to give you some good news on that front,” said Dr. Leighton. “But, unfortunately, I think the reality is that wherever ticks expand to, Lyme disease follows. And, as ticks expand beyond their current range, the number of human cases of Lyme disease and domestic-animal cases are going to increase.”

According to the federal government, between 2009 and 2021, provincial public health units reported 14,616 human cases of Lyme disease across Canada. The annual figure rose from 144 in 2009 to a preliminary estimate of 2,851 in 2021.

Dr. Leighton suggested that colder weather will help to prevent the spread of ticks to much of Western Canada, which has remained largely unaffected. Nevertheless, ticks have been found in places where they were not previously known, such as PEI and BC, which makes it imperative to continue regular monitoring of their presence across the country.

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