“[Lyme disease] is something that people care about. ... They are worried about ticks and tick-borne diseases,” explained Dr. Maarten Voordouw (PhD), assistant professor in the Western College of Veterinary Medicine’s (WCVM) Department of Veterinary Microbiology and the research team’s leader.
Lyme disease, the most common vector-borne disease in the northern hemisphere, is caused by a tick-borne spirochete bacterium called Borrelia burgdorferi that requires a tick vector and a suitable vertebrate host so it can replicate and persist in nature. The transmission cycle begins when a tick picks up the bacterium while taking a blood meal from an infected host, such as a small mammal or bird. People and companion animals are accidental hosts for the bacterium, which can cause Lyme disease in humans and dogs.
Compared to the rest of Canada, the risk of contracting Lyme disease in Saskatchewan is low. Blacklegged ticks (Ixodes scapularis and Ixodes pacificus), which transmit B. burgdorferi in Canada, aren’t common in this province. Most ticks in Saskatchewan are the American dog tick (Dermacentor variabilis), which cannot transmit the Lyme disease bacterium.
However, the situation can quickly change since ticks can migrate to new geographic locations once attached to migratory birds and other hosts.
In addition, many different strains of B. burgdorferi circulate in North America. These strains differ in their genetics, their clinical symptoms, and potentially, their transmission from different hosts. Voordouw and his team want to understand the factors that explain why some strains are common in North America, while other strains are rare.
“One of the big questions in ecology and evolutionary biology is what explains species diversity (or strain diversity): why do we have so many strains of Borrelia burgdorferi in the same ecosystem?” said Voordouw.
His team is studying several strains of B. burgdorferi commonly found in Canada. By introducing the different strains into laboratory mice (via tick bite), and then infesting these mice with ticks to compare the host-to-tick transmission success between strains, the researchers can gain information on the “fitness” of each strain in a laboratory model system.
As well, their research will hopefully provide useful information about which B. burgdorferi strains are most common in Western Canada—details that are still unknown for this region.
“In Canada, there is a perception that the diagnostic tests are not adequate. [These tests] are based on well-defined strains that are found in the eastern United States, and we know that we have different strains here in Western Canada,” said Voordouw. “So, we will be able to test whether these diagnostic tests can detect the dozen different Canadian strains that we are working with.”
With more clarity about the strain diversity of B. burgdorferi for different regions of Canada, Voordouw adds that the WCVM team’s research findings may have the potential to fine-tune diagnostic tests for Lyme disease that target western Canadians and their pets.
Voordouw is also interested in the effects of Borrelia infections on the tick vector. Parasites are constantly evolving and can eventually “learn” to manipulate the physiology and behaviour of their hosts.
“Research has repeatedly shown that mosquitoes infected with malaria are more aggressive and bite more,” said Voordouw. “[The manipulation] makes it much more favourable for the pathogen to invade the host. Parasites capable of manipulation are smarter and harder to eradicate.”
Could the same be true for ticks infected with the Lyme disease bacterium? Voordouw believes vector manipulation is less likely for Lyme disease due to the constraints on the life cycle of hard ticks.
“From my perspective, the interests of the bacteria and the tick are largely aligned. The tick wants to get a blood meal so it can become an adult and mate, and Borrelia wants the tick to take a blood meal so it can infect a host.”
Voordouw and his WCVM team received financial support from the Natural Sciences and Engineering Research Council of Canada and the Saskatchewan Health Research Foundation.