Lyme disease is caused by a bacterium called Borrelia burgdorferi which is spread by ticks.
B. burgdorferi has been found in two species of ticks in BC:
Ixodes pacificus and
Ixodes angustus, also known as western black-legged ticks.
Ticks are tiny bugs about the size of sesame seeds, that feed on blood. The ticks in BC prefer to get their blood meal from rodents and small animals. Sometimes a tick will bite a person accidentally instead of biting an animal. While most tick bites do not result in disease, some do.
Ixodes ticks are distributed throughout BC. However, most ticks that carry Lyme disease are found in southwestern BC, including Vancouver Island, the Gulf Islands, the Sunshine Coast, Greater Vancouver, and the Fraser Valley. The geographic distribution of Lyme disease in people and in ticks in BC has remained constant over time.
In BC, less than 1 percent of ticks tested carry the bacteria
B. burgdorferi that cause Lyme disease. Although the number of ticks submitted for testing has increased in recent years, the prevalence of
B. burgdorferi in ticks has remained consistently low over time. (See the chart).
Ticks live in tall grass and forested areas and attach to people or animals as they pass by. Ticks burrow part way into the skin, bite, draw blood, and then drop off. Ticks can be found year-round but they are most likely to bite in the spring (from March to June).
The risk of Lyme disease in BC is lower and more stable than it is in eastern and central Canada and in the northeastern USA. In these regions, Lyme disease rates in humans and ticks have increased with climate change. Reasons for this difference include:
• The ticks species capable of carrying Lyme disease in BC are different.
I. pacificus and
I. angustus (western black-legged ticks) are less capable of carrying
B. burgdorferi than
I. scapularis (black-legged tick), the tick in eastern Canada.
• The animals on which ticks feed are different. In BC, ticks feed on small rodents such as deer mice and dusky-footed woodrat. In eastern Canada and the USA, ticks feed on white-footed mice and white-tailed deer.
• The vegetation and climate are different between BC and eastern Canada (e.g. BC has mostly coniferous forests, whereas eastern Canada has mostly leafy forests).
• Ixodes ticks are present throughout southern and central BC, including in most of the highly populated areas. An expansion of the range of these ticks, which could occur with climate change, will not greatly increase the number of people exposed in BC.