HMN 2026: What is the other tick-borne disease to avoid: Anaplasmosis in Canada

Move over, Lyme disease—there’s another tick-borne disease to worry about in Canada. Anaplasmosis, the second-most common tick-borne disease in the country, can cause a range of health issues, including myocarditis, as a practice article in the Canadian Medical Association Journal shows.

“As the incidence of tick-borne diseases rises rapidly across Canada … considering anaplasmosis as a possible pathogen is increasingly important for front-line clinicians,” writes Dr. Michael Quon, a general internal medicine specialist and clinician investigator at The Ottawa Hospital and an assistant professor at the University of Ottawa, Ottawa, Ontario, with co-authors.

Anaplasmosis is a growing public health concern as blacklegged ticks, the main vector, have moved into many Canadian provinces. Cases primarily occur in Ontario, with an increase noted in Quebec and Manitoba.

The case describes a 79-year-old man from a rural area of eastern Ontario who visited a local community hospital with fever, fatigue, chills and weakness that led to a fall. He had an autoimmune disease and was receiving immunosuppressive treatment. The patient could not recall any tick bites or earlier Lyme disease, but he worked regularly in the woods.

Physicians suspected the symptoms were from an infection and ordered a range of tests to investigate, including a blood smear and polymerase chain reaction (PCR) test, and started him on broad-spectrum antibiotics, including doxycycline, given the clinical suspicion of tick-borne disease.

The PCR test was positive for anaplasmosis, and the medical team completed treatment with doxycycline for 14 days, which would also treat any potential coinfection with Lyme disease. Testing confirmed a diagnosis of myocarditis, which has previously been reported only once as a complication of anaplasmosis. After eight days, the patient was discharged, and after four months, he had no symptoms and normal heart function.

Anaplasmosis symptoms are often nonspecific, with fever, weakness, headache and gastrointestinal distress.

“This case highlights the importance of considering tick-borne diseases as part of the infectious workup in endemic regions. Patients should be asked about tick exposures, proximity to deer or pets, use of preventive measures (N,N-diethyl-meta-toluamide [DEET], protective clothing, and skin inspections), and prior Lyme disease. However, the tick-borne diseases are challenging as 50% to 75% of patients with early Lyme disease do not recall tick bites,” the authors write.

“Empiric antimicrobial therapy with doxycycline should not be delayed in a patient with a suggestive clinical presentation. Initiation of effective treatment in anaplasmosis is associated with favorable outcomes, even in patients with complications.”

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