Tick-borne relapsing fever in British Columbia: A 10-year review (2006–2015)

Background: Tick-borne relapsing fever is one of the oldest tickborne diseases identified in British Columbia. The causative agent is the spirochete Borrelia hermsii, which is transmitted to humans by the night-feeding soft-shelled tick Ornithodoros hermsi found in southeastern British Columbia and the northwestern United States. The identification of this illness is made difficult by the fact that tick-borne relapsing fever is not a reportable illness in BC and laboratory diagnosis can be challenging. The innocuous feeding pattern of the vector tick means bites can go unnoticed, while the typical 7-day delay in symptoms means patients often do not become ill until after they have left a diseaseendemic area where physicians are more likely to recognize the illness. Identification and treatment of this illness is important because it can cause long-term sequelae, including cardiac and renal disturbances, peripheral nerve disturbances, ophthalmitis, and complications during pregnancy. A report on a 10-year review of cases in BC was proposed to alert physicians to the presence of this infectious disease and explain how to submit blood samples for testing to the BC Centre for Disease Control Public Health Laboratory. Methods: From 2006 to 2015, the BC Centre for Disease Control Public Health Laboratory received 112 samples from 100 patients suspected to have tick-borne relapsing fever. These samples were analyzed using dark field microscopy, immunofluorescence assay, western blot testing, and polymerase chain reaction assay. A review of the laboratory findings was conducted and the diagnostic challenges and sample requirements were considered. Results: The 100 patients (57 male, 43 female) whose 112 samples were analyzed during the review period ranged in age from 6 to 83 years, and most (67%) were either young or middle-aged adults (20 to 60 years). Of these patients, 19 tested positive for B. hermsii (12 female, 7 male). Except for 2009 and 2014, at least one case of tick-borne relapsing fever was identified each year, with the top year being 2007 (seven cases). Most of the positive cases were associated with the Thompson-Okanagan region. Polymerase chain reaction assay and Giemsa stain testing yielded the highest proportion of positive results (4 of 11 samples) followed by immunofluorescence assay for IgG antibodies (19 of 109). Conclusions: The high proportion of positive results (19%) may be due to the submission of mainly very characteristic samples received from an endemic area. Many physicians may not be aware of the presence of B. hermsii tick-borne relapsing fever in BC and therefore do not request testing. Physicians should note that patients are unlikely to report a painless tick bite received during sleep and that the key symptom is a sudden, high fever (39.2 °C or higher) that follows an incubation period of approximately 7 days and lasts 3 to 7 days. An asymptomatic period of 7 days is then followed by an average of two relapses. General infections considered in the differential diagnosis should include salmonellosis, bartonellosis, tularemia, and leptospirosis. Patients should also be asked about foreign travel to rule out a range of other infections such as malaria, kala azar, yellow fever, and sand fly fever. Blood samples for identifying the causative This article has been peer reviewed.