
Tick paralysis is an appropriately albeit unoriginally named form of ascending paralysis that's been impacting residents of the southern BC Interior since at least as far back as the late nineteenth century and potentially even farther back than that.
Globally, several species of ticks are known to cause tick paralysis but in Canada we primarily need to worry about one: the Rocky Mountain wood tick (Dermacentor andersoni). Most cases of tick paralysis in Canada occur within the range of this tick species although, notably, not the entire range. The dryland areas of south-central BC are the epicentre of tick paralysis in North America despite the geographic range of Rocky Mountain wood ticks including Alberta and, to a lesser extent, Saskatchewan in addition to several US states. No one knows why the southern BC Interior is home to the lion's share of cases despite more than a hundred years of research.
Not only are the paralyzing ability of Rocky Mountain wood ticks primarily limited to one region within their territory, there is great variation in the number of cases within that region from one year to the next.
Tick paralysis is unlike any other tick-borne illness in Canada in that its symptoms aren't caused by a pathogen, but rather by toxic components contained in the tick's saliva. Although the toxin responsible for tick paralysis in Canada hasn't yet been isolated from Rocky Mountain wood ticks, it's believed to be a similar to or the same as toxins that have been isolated from several ticks species around the globe.
A female Rocky Mountain wood tick usually needs to be attached several days for paralysis symptoms begin to set in. The primary symptom is weakness or numbness in the legs followed by a lack of coordination that gives way to paralysis. If left untreated, symptoms will progress to the arms and finally the respiratory system. Once breathing is compromised, the patient will likely die.
Treatment is simple: Search the patient for one or more attached ticks and remove them. The short-lived toxin will abate and the patient will start to recover almost immediately and return to full health in a matter of hours or days.
Humans aren't the only ones who suffer from tick paralysis. Cattle, dogs, marmots and sheep are among the mammals impacted. Many others, including cats, appear to be immune.
It should be noted that sometimes, in very rare cases, tick paralysis can also be caused by American dog ticks (Dermacentor variablilis), which are ubiquitous in several places in central and eastern Canada. Horses in Manitoba appear to be particularly susceptible.