
TBRF is one of the oldest known tick-borne illnesses in this country, with documented cases in the BC Interior stretching as far back to the early 1930s.
TBRF is something of an enigma. Despite being one of the earliest recognized of the tick-borne illnesses in Canada, it's tragically under-researched both in this country and in the US, so there remains a staggering amount we still don’t know about it. But there’s one thing that we do: TBRF is caused by infection with a bacterium that's closely related to the ones (Borrelia burgdorferi sensu lato) that cause Lyme disease.
Most cases of TBRF in North America are thought to be caused by Borrelia hermsii although it's possible a minority are caused by another species in the relapsing fever group of borrelia bacteria, most notably Borrelia parkeri of which little is known.
Unlike Lyme bacteria, which is transmitted in BC primarily by western blacklegged ticks (Ixodes pacificus) and, to a lesser extent, by Ixodes angustus ticks (no common name), TBRF is thought to be transmitted by night-feeding, soft-bodied Ornithodorus hermsi ticks.
I say "thought to be" because although TBRF has long been associated with Ornithodorus hermsi ticks in the US, no tick in BC of any species has ever been found to be infected with Borrelia hermsii bacteria despite an almost 100 year history of humans acquiring the disease and efforts by scientists to capture infected ticks at the locations where those infections have occurred. That leaves a very big question as to whether Ornithodorus hermsi really is the primary agent of TBRF in BC or if another yet-to-be identified tick is involved. The smart money is on Ornithodorus hermsi but, as the gambling analogy suggests, that isn't a sure bet.
Virtually all cases of TBRF documented in Canada were contracted in BC’s southern interior, most notably in the Thompson-Okanagan and Kootenay-Boundary regions. However no one really knows TBRF's full range. With cases likely being misattributed to more common diseases and the lack of a smoking gun in the form of the pathogen being isolated from a tick collected in the province, it's difficult to say what the geographic range of TBRF truly is.
A 2017 report noted there are a surprisingly high number of TBRF cases in BC compared with other regions in the Pacific Northwest where the disease is endemic, and a disproportionate number of BC patients simultaneously test positive for both TBRF and Lyme disease. It’s possible that cross-reactivity between two tests for very similar pathogens plays a role in that. Cross-reactivity can happen when indirect antibody tests are used to test for the presence of organisms that produce similar antibodies — such as two different species of borrelia — causing the tests to come up positive for the real infecting pathogen and the similar one, making it appear as though someone has both diseases when really they have one infection that has reacted on both tests.
That may be all that’s happening in BC. But enough researchers have noted the curious double positives that it has raised an important question: Are British Columbians contracting TBRF and Lyme disease from a single tick bite? The sad fact is there hasn’t been enough research for anyone to make a definitive statement on the subject. Instead we have to rely on studies done in the US and meagre research in BC to make a hazy guess. (It should be noted that American research into TBRF is also not that robust although there is more of it than there is in Canada.)
If there is one thing we have learned from the decades of tick-borne illness research in Canada, it’s that the situation in this country doesn’t always mirror the situation in the US, so the more research that can be done on TBRF in BC, the more likely it is that we will come up with answers to the myriad questions that are still outstanding, which will either verify the findings in the US or take us in a whole new direction.
Photo of Borrelia hermsii courtesy of the National Institute of Allergy and Infectious Diseases (NIAID)