The incidence of tick-borne illnesses in Canada is on the rise. Diseases that were once limited to the United States have spread north, and rare infections are becoming more common. Especially during the summer months, when diagnoses are most common, it's important for clinicians to keep an eye out for these illnesses.
Tick-borne illnesses present in Canada include Lyme disease, anaplasmosis, babesiosis, and Powassan virus. While Lyme disease is the most common illness, clinicians must be aware of each of these illnesses, Heather Coatsworth, PhD, a research scientist at the National Microbiology Laboratory in Winnipeg, Manitoba, Canada, told Medscape Medical News.
This awareness is particularly important in hot spots with established populations of Ixodes tick species (commonly referred to as deer ticks), which carry the pathogens. Cases tend to be concentrated in pockets of southern Ontario, Quebec, and Nova Scotia.
Leaving aside Lyme disease, "anaplasmosis is the heaviest hitter," said Coatsworth. "We're seeing a lot more cases, especially in Nova Scotia and Ontario." Babesiosis, a parasite that causes malaria-like symptoms, is increasing more slowly. In 2023, 40 cases of anaplasmosis and 15 cases of babesiosis were reported in Ontario. Powassan virus is more sporadic (21 total cases had been reported in Canada as of 2017) but can cause encephalitis and has a higher fatality rate. Mortality is about 10% among patients who contract a brain or spinal cord infection from the virus.
Case numbers are much lower in western Canada due to differences in tick species. A few cases of relapsing fever caused by bacteria spread by a western tick species have also been identified in British Columbia. As infections become more common, it's important that clinicians know how to treat, diagnose, and report each of these illnesses, said Coatsworth.
Increasing Prevalence
In 2009, 144 cases of Lyme disease were reported. The annual number of cases now consistently surpasses 2500, though it varies somewhat according to weather conditions. Typically, dry, cold winter conditions kill off significant portions of the tick population, thus preventing the arachnids from reaching maturity and spreading disease; milder winters tend to result in more ticks.
Climate change is making warmer weather patterns more common. This change has contributed to the overall rise in cases, said Gerald Evans, MD, chair of the Division of Infectious Diseases and professor of medicine at Queen's University in Kingston, Ontario, Canada. Increased temperatures have allowed tick populations to expand and move north, bringing new infections with them. "Now we have established reservoirs for a lot of these pathogens," he said.
In addition, more Canadians are living outside urban areas. "People now live in homes that border on wildlife areas," said Evans. Ticks rely on small mammals for food, so living near wildlife means being near more ticks. "The result of that is that they're coming into the interface where the likelihood of tick exposure is high."
Surveillance and Testing
Tick-borne illnesses found in Canada tend to present with flu-like symptoms following a bite. While Lyme disease is associated with a rash, other tick-borne illnesses aren't associated with this telltale sign.
Testing and surveillance have improved in recent years, said Muhammad Morshed, PhD, a clinical microbiologist and the program head of zoonotic diseases and emerging pathogens at the British Columbia Centre for Disease Control Laboratory, Vancouver, British Columbia, Canada. Now, the Canadian government provides reliable diagnostic testing for tick-borne illnesses at sites including the National Microbiology Laboratory, and it has taken steps to better track cases and monitor tick populations.
Surveillance of tick populations comprises two main methods. The first actively monitors populations through "tick dragging," in which a cloth is dragged across vegetation to collect ticks, which are then tested for pathogens. A citizen science project called eTick also allows Canadians to submit photos of ticks to be identified by entomologists. If the tick is not an Ixodes species, it likely is not infectious. But a tick carrying a pathogen won't necessarily transmit it, Morshed noted. "Ticks have to be on the human body for at least 16-24 hours" to transmit pathogens.
Treatment and Prevention
Identifying and treating tick-borne illnesses early is key to preventing detrimental effects. Lyme disease goes through several phases, said Evans, who routinely treats patients with Lyme disease at Kingston Health Sciences Centre, Kingston, Ontario, Canada. If patients are treated when the disease is localized, then Lyme disease can be limited to a rash and mild symptoms. But "if they don't get treated, then the organism will disseminate." Disseminated Lyme disease can cause neurologic symptoms including Bell's palsy or meningitis, as well as atrioventricular block. Once treated with antibiotics, the symptoms resolve.
Anaplasmosis can be harder to identify, but both illnesses are treated with the antibiotic doxycycline. Babesiosis requires two medications (usually azithromycin and atovaquone). Anaplasmosis and babesiosis usually can be identified with a blood smear, which can be faster than serology testing, said Evans. No specific treatments for Powassan virus are available.
Simple steps can easily prevent tick-borne illnesses. Wearing protective clothing and using an insect repellent with DEET or picaridin can keep ticks from biting, and light-colored clothing can make them easier to spot. If a tick does attach itself, removing it quickly will likely prevent disease. To transmit the Lyme disease–causing bacteria, a tick must be attached to the human body for hours. A timely, thorough tick check can prevent most infections.
Gwendolyn Rak is a health reporter for Medscape Medical News based in Philadelphia.