tick-borne infections
in review
3 min read
Updated 2026-09-29
tick-borne infections
Blacklegged ticks (Ixodes scapularis; I. pacificus in BC) are expanding across southern Canada — Ontario, Quebec, the Maritimes, Manitoba — and carry Borrelia burgdorferi (Lyme), Anaplasma, Babesia, and Powassan virus. Erythema migrans is a clinical diagnosis — treat without serology: doxycycline 100 mg BID × 10 days. Lyme carditis with PR ≥300 ms → admit, IV ceftriaxone. Prophylaxis: doxycycline 200 mg × 1 within 72 h for a high-risk Ixodes bite. Fever + cytopaenias + raised transaminases after a tick bite → anaplasmosis (doxycycline) or babesiosis (atovaquone + azithromycin).
tick bite prophylaxis
Single doxycycline 200 mg (4.4 mg/kg in children) within 72 h of removal if all of:
- Ixodes tick
- attached ≥36 h (or engorged)
- acquired in an area where blacklegged ticks are established/Lyme risk is recognised
Remove with fine tweezers close to the skin; no serology after a bite.
lyme disease
| stage | features | treatment |
|---|---|---|
| early localised (3–30 days) | erythema migrans ≥5 cm, expanding (may lack central clearing), ± flu-like illness | doxycycline 100 mg BID × 10 days; or amoxicillin 500 mg TID × 14 days; or cefuroxime 500 mg BID × 14 days; azithromycin second-line |
| early disseminated (weeks) | multiple EM | as above |
| facial nerve palsy (may be bilateral), meningitis, radiculoneuritis | doxycycline PO 14–21 days — as effective as IV ceftriaxone 2 g daily | |
| carditis — AV block (can fluctuate to complete), myopericarditis | PR ≥300 ms, symptoms, or higher-grade block → admit, telemetry, IV ceftriaxone 2 g daily → oral once improving; 14–21 days total; temporary pacing if needed (usually resolves — avoid permanent pacemaker early) | |
| late (months) | Lyme arthritis — large-joint (knee) mono/oligoarthritis, large effusions | doxycycline PO × 28 days; persistent → second oral course or IV ceftriaxone 2–4 weeks; post-antibiotic arthritis → rheumatology (DMARDs, synovectomy) |
| late neuroborreliosis (encephalomyelopathy, neuropathy) | IV ceftriaxone 2–4 weeks |
- serology: two-tier (EIA → immunoblot, or two EIAs); negative early in EM — do not test EM; positive by the time of disseminated/late disease; IgM alone after >30 days of symptoms is unreliable
- post-treatment Lyme disease syndrome (fatigue, pain, cognitive complaints): prolonged antibiotics do not help
- Jarisch–Herxheimer-like reaction can follow the first dose
anaplasmosis
- fever, headache, myalgia 1–2 weeks after a bite; leucopaenia, thrombocytopaenia, raised ALT/AST; morulae in neutrophils (insensitive); PCR
- doxycycline 100 mg BID × 10–14 days (covers Lyme coinfection) — start empirically; defervescence within 48 h expected — if not, reconsider (babesiosis coinfection)
babesiosis
- intraerythrocytic parasite; fever, haemolytic anaemia, thrombocytopaenia, raised LDH/bilirubin; severe in asplenia, older adults, immunosuppression (rituximab)
- smear: ring forms, tetrads (“Maltese cross”); PCR; also transfusion-transmitted
- atovaquone 750 mg BID + azithromycin × 7–10 days (IDSA 2020); severe → IV azithromycin + oral atovaquone
- exchange transfusion for high parasitaemia (>10%) with severe haemolysis or organ dysfunction
- immunocompromised → longer courses (≥6 weeks) until smears negative for 2 weeks
other tick-borne infections in Canada
- Powassan virus (Ixodes): encephalitis — supportive; see encephalitis
- Rocky Mountain spotted fever (Dermacentor; rare in Canada, more in US): fever + rash spreading from wrists/ankles → doxycycline at any age
- tularaemia (ticks, rabbits): ulceroglandular — gentamicin or doxycycline/ciprofloxacin
- coinfection (Lyme + Anaplasma + Babesia) → suspect with unusually severe illness or failure to respond
traps
- sending Lyme serology for erythema migrans (and withholding treatment while waiting)
- missing Lyme carditis in young patients with new AV block
- labelling a single tick bite without the three criteria as needing prophylaxis
- long-term antibiotics for post-treatment symptoms
- doxycycline-unresponsive “anaplasmosis” — check a smear for Babesia