Emerging into Lyme
Lyme disease is now the most common vector-borne disease in Canada and the USA. Caused by the bacterium Borellia burgdorferi and transmitted by the bite of an Ixodes tick, Lyme disease is increasing rapidly in both countries but especially in Canada. Until recently, there was just one location in central and eastern Canada, near Lake Erie, where the tick was known to persist year round. By 2020, it’s estimated that 80% of Canadians in this part of the country will be living in such areas.
Lyme is an emerging disease. Borrelia’s northward march has been provoked not by a genetic mutation but by our actions – as has generally been true with emerging diseases – global warming in this case. Lyme’s been able to make the trek because the tick and the animals it feeds on are all moving north. The tick’s larvae and nymphs feed on birds or small mammals. The white-footed mouse is their most abundant and reliable host and the Borrelia they leave it with do the mouse no apparent harm. The mouse has been moving north at about 10 km/yr over the last four decades. Adult ticks feed on larger mammals, notably the white-tailed deer, which has become more numerous in southern Canada and has spread well into the boreal forest.
The march north is made possible by the character of these players: each in its own way is a generalist. None is a fussy feeder or inordinately attached to a particular habitat. That’s a pretty good description of us but humans are bit players in Borrelia’s life story. We’re what are known as dead-end hosts: once infected, we’re unlikely to pass it on via another tick bite. Our role has been to orchestrate the changes that enable the spread.
Behind the expanding front, other factors along with temperature affect the abundance of ticks and the Borrelia they carry. The density and diversity of rodent hosts appears to be key and can be affected by habitat fragmentation. The spread of the coyote – the supreme generalist – across the continent over the last century is thought to have played a role in displacing the red fox which is an excellent mouse predator. However, Nicholas Ogden, a senior research scientist at the Public Health Agency Canada, says that this knowledge has yet to yield any reliable and acceptable measures of environmental management aimed at preventing Lyme disease. Limiting global warming to 1.5° didn’t come up in our conversation but would surely help, and not just with Lyme.
West of Manitoba there’s no evidence that Lyme is emerging. The Ixodes tick seen in the east is rare in Saskatchewan and Alberta, apparently because conditions are too dry. In BC another tick species is prevalent and its nymphs stick close to the ground where people are less likely to brush up against them. Reported Lyme cases have hovered between 25 and 40 cases per year in BC, many of these acquired elsewhere, according to the BC Centre for Disease Control.
With no vaccine on the market, preventing Lyme disease is mostly an individual responsibility. Tucking your pants into your socks, showering after being outdoors and checking yourself and your children daily for ticks are among the measures recommended (check out the Federal and BC prevention guides for more information).
Lyme disease is emerging not just “out there” but also in our awareness and understanding. The number of cases reported to Health Canada rose almost four-fold between 2011 and 2016 in part because the public is learning what a tick bite can mean and physicians are learning how to diagnose the disease.
Infections treated early with 2-3 weeks of antibiotics are usually resolved. But they’re not always diagnosed: many of the symptoms are not distinctive – fever, fatigue, joint pain. One symptom is unusual: a sharply defined rash around the tick bite, often resembling a bullseye, but not everyone develops it. Tick bites are easily missed: they’re painless and the tick is small and may drop off before it’s noticed.
Symptoms are more severe and antibiotics are less effective the longer treatment is delayed. Even with treatment, some 10-20% of patients have symptoms, including arthritis and cognitive, neurological and cardiac manifestations that can persist for months or years, referred to as Posttreatment Lyme disease syndrome (PTLDS).
Diagnostic tests aren’t able to detect infection in the early stage. They are more sensitive in later stages but after antibiotics have been taken cannot distinguish active from past infection. There is no test for PTLDS because there is no agreement on what causes it. There is also no government-approved treatment for it in the US or Canada.
The Infectious Diseases Society of America issued Clinical Practice Guidelines for Lyme disease in 2006 which continue to inform medical practice in the US, Canada and Europe. They state that antibiotic treatment longer than 2-3 weeks is not justified because there is no evidence of persistent infection (although the tests couldn’t tell if there was). The guidelines suggest that “in many patients, posttreatment symptoms appear to be … related to the aches and pains of daily living”.
Many patients with severe health complaints say they are dismissed by the mainstream physicians they consult. There are other doctors who treat such patients with antibiotics and supportive therapy for longer periods, sometimes more than a year, and claim success with some. They refer to themselves as Lyme-literate doctors. I’ve heard mainstream physicians, on both sides of the Atlantic, refer to them as “quacks”.
The dissension is loud and persistent. A trial in the Netherlands of antibiotic treatment for PTLDS – longer than ISDA guidelines stipulate but shorter than Lyme-literate doctors typically follow – was interpreted very differently by stakeholders from the two sides. A recent study claiming to have found intact Borrelia and their remnants after antibiotic treatment in and near inflamed tissues in heart, brain, muscles and joints – potentially relevant to an understanding of PTLDS – was categorically dismissed by mainstream researchers.
It is striking how little, practically, has changed in 15 years in terms of the treatment and diagnosis of Lyme as well as its prevention. Innovation lags far behind the spread of the disease and the burden it imposes.
Emerging diseases, almost by definition, are poorly understood initially. Valuing the insights of all who confront them, particularly patients, communities and health workers on the front lines, has been key to progress in other contexts. ACT UP changed research and treatment agendas on HIV in the US and Canada through its well-informed and compelling actions inside institutions and in the street. During the 2014-15 Ebola epidemic in West Africa, ideas from affected communities and researchers working with them helped identify ways to slow the virus’ spread. Lyme needs new ideas from research on how Borellia makes people sick. It also needs to examine the experience of doctors and their patients outside the mainstream, derive new treatment ideas from that experience and test them rigorously. Disdain slows us down.