Know your ticks: Western blacklegged tick (Ixodes pacificus)

Western blacklegged ticks (Ixodes pacificus) were first identified in 1904 and haven't been intensively studied in Canada, so a lot of the information we have is the product of research efforts that have been undertaken in the western US and occasional initiatives in this country.

What's known is that this species is the primary transmitter of Lyme disease in British Columbia where it's widespread especially in coastal regions, on the Gulf Islands and Vancouver Island, and in the southern valleys of the Interior where these ticks tend to hang out in Douglas fir forests. People most frequently encounter them when brushing vegetation along the edges of hiking trails or on south-facing slopes. In the more temperate coastal regions of British Columbia, where temperatures rarely drop below freezing, adults western blacklegged ticks can be active all year round.

Like the more familiar blacklegged tick (Ixodes scapularis) -- the primary transmitter of Lyme disease in all of Canada except BC -- western blacklegged ticks feed on a wide variety of creatures in order to obtain the blood they need to propel their lifecycle. Adults primarily target large to medium-sized mammals such as cats, deer, dogs and sheep although they're just as happy to feed on humans. Immature western blacklegged ticks feed on small mammals, birds and reptiles and are particularly fond of deer mice and northern alligator lizards. Squirrels may also be important hosts.

Adult western blacklegged ticks are most abundant between February and June and although they frequently bite people, they're believed to be inefficient transmitters of Lyme bacteria and cause just a handful of Lyme disease in BC cases each year. They also transmit babesia, anaplasma and Borrelia miyamotoi singularly and as co-infections with each other and/or with Lyme disease although these kinds of multiple infections are more common in eastern Canada.

Diseases transmitted: Anaplasmosis, babesiosis, Borrelia miyamotoi disease, Lyme disease.

Where found: Widespread throughout BC.

Photo by: CDC/ James Gathany