The reason Lyme disease is on the rise in Canada is thought to be a combination of greater awareness, increased reporting and climate change.
"We've truly noticed the tick is spreading for sure. What its relation to climate change, don't know," said Dr. Gregory Taylor, Canada's chief public health officer.
In 2015, more than 700 cases of Lyme disease were reported to the Public Health Agency of Canada, compared with 140 cases in 2009.
Lyme disease became a nationally notifiable disease in 2009, which makes it a priority for the federal, provincial and territorial governments to monitor and control.
As more cases arise, doctors are still getting used to reporting them to public health departments, said Dr. David Fisman of the Dalla Lana School of Public Health in Toronto. He has studied how ticks expanded northward into the most heavily populated areas of Canada.
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"I think the increase is real and I think the culprit is climate change," Fisman said.
Fisman is also studying El Nino effects of warmer, wetter weather on ticks. "The ticks can now establish endemic thriving populations in areas that used to be too cold for them to complete their life cycles."
The ticks' habitat is also changing. More ticks are surviving the winter and making it through the grass at the edge of forests, said Sandy Smith, a professor in the forestry department at the University of Toronto, where she studies invasive forest pests.
As people hike and bike in wooded and grassy areas, a tick can climb on. The longer it's attached, the greater the possibility it can transmit Lyme disease bacteria. People have hours to remove the tick before that happens.
Blacklegged ticks spread Lyme disease throughout most of Canada and the western blacklegged tick does so in British Columbia. The ticks feed on a series of hosts, starting with small mammals such as mice.
Ticks are tied to populations of white-tailed deer and rodents. As hunting declines and deer numbers increase in Canada, the large animals act as a greater reservoir for their ticks, Smith said.
Deer are good at spreading blacklegged ticks but they generally don't carry it far, said Janet Sperling, a PhD candidate in entomology at the University of Alberta and a board member at CanLyme, which advocates for people with the disease.
Birds can carry ticks for long distances and drop them in unexpected places, Sperling said. "There is nowhere in Canada where Lyme disease can be ignored."
Sperling also said there is no question ticks are spreading in Canada and much of the change is due to changing climate and land use changes.