Lyme disease is a vector-borne disease that’s transmitted by blacklegged ticks (Ixodes scapularis) carrying the bacterium Borrelia burgdorferi. Once infected, ticks can transmit the disease to humans, dogs, and other hosts through feeding on their blood.
In people, early signs of infection include flu-like symptoms and a characteristic red, circular rash that looks like a bull’s-eye pattern. However, since not everyone develops these symptoms, many cases of Lyme disease go undetected.
Unfortunately, some people affected by the bacteria — even those who are diagnosed and treated with antibiotic drugs — never fully recover after treatment. Many continue to suffer for months to years from problems such as significant fatigue, widespread pain, cognitive issues and sleep disruption. This condition is described as post-treatment Lyme disease syndrome (PTLDS).
In Canada, the annual number of reported Lyme disease cases has increased sixfold over the last decade and researchers anticipate that this trend will continue. Not only do ticks prefer warm and humid environments, but white-footed mice and white-tailed deer, common hosts for B. burgdorferi, are also expanding their range due to climate change and shifts in agricultural land use.
Dr. Maarten Voordouw, an associate professor at the Western College of Veterinary Medicine (WCVM), and his research team are investigating the ecology (relation of organisms to one another) of Lyme disease. Understanding the interaction between Lyme bacteria, their vector and their vertebrate hosts is crucial to Lyme disease management and risk mitigation.
Although scientists have tracked the spread of Lyme disease across Canada, the medical community has limited data on disease outcomes and cases of persistent symptoms — no one can reliably estimate the prevalence of PTLDS patients in Canada.
In a 2014 survey of over 3,000 Lyme disease patients, about half of the respondents reported dealing with the after-effects of Lyme disease — such as poor physical and mental health status — for over 10 years.
This study suggested that chronic Lyme disease patients suffer worse than people diagnosed with other chronic diseases such as diabetes, congestive heart failure and arthritis. Survey results also emphasized the negative impacts that lingering health issues have on quality of life (chronic Lyme disease is associated with high disability and unemployment rates) as well as the urgent need for the diagnosis and innovative treatment for these patients.
However, PTLDS continues to be a conundrum in both research and clinical fields. Only a limited number of studies focus on Lyme patients with persistent symptoms, and no standardized medical treatments are available for people suffering from PTLDS.
One critical concern is that a significant number of physicians don’t believe in PTLDS since there’s no clinically detectable infection. Current antibody testing for B. burgdorferi, the only test approved by the U.S. Food and Drug Administration (FDA), isn’t very sensitive — meaning that false negative results are common.
Studies have also found that prolonged courses of antibiotic drugs don’t relieve the symptoms for PTLDS patients, which contradicts the hypothesis that PTLDS is caused by a persistent bacterial infection. As many other chronic diseases can also have similar symptoms, it’s very challenging to diagnose PTLDS and agreeing on treatment options is hard to achieve without fully understanding the underlying cause of the persistent symptoms.
Another popular hypothesis of what causes PTLDS is host immune dysregulation — when the body can’t control or restrain its own immune response. Since B. burgdorferi can’t produce any toxin that damages host tissues directly, the symptoms of Lyme infection are mainly caused by the host’s immune response. Researchers suggest that for PTLDS patients, their inflammatory and auto-immune responses are disrupted and dysregulated, giving rise to persistent symptoms.
Although the study of prolonged immune response in PTLDS patients is in an early stage, the COVID-19 pandemic has brought more attention to chronic illnesses. According to the World Health Organization, long COVID is a chronic disease 90 days after the infection of COVID-19.
Just like PTLDS patients, long COVID patients suffer from fatigue, pain and insomnia — non-specific symptoms that researchers believe may be caused by an auto-immune reaction. Interestingly, a recent study suggested a common biological pathway between long COVID patients and those diagnosed with Lyme disease.
In an era where COVID-19 has dominated the attention of health care professionals and researchers for more than three years, hopefully the tremendous support of research investigations targeting long COVID may result in more understanding of chronic illness and benefit the underfunded Lyme disease communities.
Arial Wei of Chengdu, Sichuan, China, is a third-year veterinary student at the Western College of Veterinary Medicine (WCVM) who worked as a summer research student in 2022 with Dr. Maarten Voordouw. Her story is part of a series of articles written by WCVM summer research students.