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Tick populations and their diseases spreading as the climate warms

The black-legged tick, often called the deer tick, is spreading dramatically through the U.S. and Canada, The spread has also caused an increase in the incidence of Lyme Disease. Image - Scott Bauer/PD-USGov-USDA-ARS Public Domain
The black-legged tick, often called the deer tick, is spreading dramatically through the U.S. and Canada, The spread has also caused an increase in the incidence of Lyme Disease. Image - Scott Bauer/PD-USGov-USDA-ARS Public Domain

Climate change has caused tick populations to increase dramatically and spread into urban areas throughout the United States and Canada, particularly the black-legged tick (scientific name Ixodes scapularis), also known as the deer tick.

Black-legged ticks also are carriers of Lyme disease, and while they are usually found in forests, wooded areas, and on shrubs, leaves, and long grass, they have increasingly moved into urbanized areas, increasing the risk that humans will become infected with the disease.

Discussing the spread of Lyme Disease in Canada, Heath MacMillan, a biology professor at Carleton University, told CTV’s Your Morning that climate change has impacted the movement and spread of tick populations, causing them to move out of their traditional habitats and into urban environments.

“This year we had a particularly mild winter, especially in southern Ontario, and also a wetter winter,” MacMillan said in an interview on Friday. “This is something that is happening more and more frequently. We’re having winters like this because of climate change, where we’re not getting as much snow cover, we’re not getting as much constant low temperatures, and this is something that makes ticks survive better in the winter which means we have more in the spring.”

According to Health Canada, between 2009 and 2019, the number of cases of Lyme disease jumped from 144 cases in 2009 to 2,636 cases in 2019, with over 88 percent of the reported cases of Lyme disease in 2016 coming from Ontario, Quebec and Nova Scotia, 

Lyme Disease in the United States is also increasing as ticks spread into areas not usually associated with Lyme disease. Each year, approximately 30,000 cases of Lyme disease are reported to CDC by state health departments and the District of Columbia.

The geographic distribution of high incidence areas with Lyme disease appears to be expanding based on data reported to National Notifiable Disease Surveillance System (NNDSS). Following are two maps, one of the U.S. and one for Canada, and both focus on the case loads for Lyme disease on the Eastern half of the two countries. It is easy to see how the tick population has spread to the north.

Each dot represents one case of Lyme disease and is placed randomly in the patient’s county of residence. May courtesy of the CDC, under Public Domain.
Provinces highlighted in the map include Quebec (French only) New Brunswick, Nova Scotia, Ontario, Manitoba, and British Columbia. Map courtesy of Health Canada, Public Domain

Health Canada and the CDC both recommend that when going outdoors, people should be cautious and take certain measures to protect themselves. “Ticks can’t jump, they climb onto us from vegetation low-down, so essentially if you’re wearing stuff that covers your skin, they are less likely to get access to your skin and to bite you,” MacMillan said.

CDC researchers have discovered that a naturally occurring compound called nootkatone, found in grapefruit, Alaska yellow cedar trees, and some herbs, can kill or repel ticks and insects. On August 10, 2020, the Environmental Protection Agency (EPA) registered nootkatone, an active ingredient discovered and developed by DVBD, for use in repellents and insecticides.

The product is expected to be on the market by 2022. Currently, permethrin-treated clothing is still a good way to repel ticks. Studies have shown that treated fabric is highly irritating to ticks, causing them to drop off – stunting their activity for more than 24 hours afterward.


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We are deeply saddened to announce the passing of our dear friend Karen Graham, who served as Editor-at-Large at Digital Journal. She was 78 years old. Karen's view of what is happening in our world was colored by her love of history and how the past influences events taking place today. Her belief in humankind's part in the care of the planet and our environment has led her to focus on the need for action in dealing with climate change. It was said by Geoffrey C. Ward, "Journalism is merely history's first draft." Everyone who writes about what is happening today is indeed, writing a small part of our history.

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