The Tick’n Bomb in Your Differential (Not The One You Think)

Putting my Global Health fellowship to good use presenting on Immigrant Health to UBC residents.

-Simon

Don't let this diagnosis tick you off. 

Stop waiting for the rash. When Rocky Mountain Spotted Fever (RSMF) is on your differential, delaying treatment while you wait for laboratory confirmation can lead to devastating clinical outcomes. A recent CMAJ review from 2026 highlights that human cases are rare but endemic in parts of Canada.

Early recognition requires a high index of suspicion based entirely on exposure history. While the classic maculopapular rash begins on the wrists and ankles before spreading centrally, it is completely absent in up to twelve percent of cases - so don’t get caught by a rashless RMSF!  

Clues on History

Ask about hiking, camping, & gardening in affected regions across Canada

Clues on Initial Labwork

When I did part of my Global Health fellowship at Toronto General Hospital I was trained to look for subtle clues on the CBC:

• elevated liver enzymes can mean Mono;

• reduced WBC count can suggest Dengue.

RSMF is no different: 

• Watch for supporting laboratory clues like thrombocytopenia, hyponatremia, combined with elevated liver enzymes. 

Your immediate management plan should involve a multi-pronged diagnostic and therapeutic approach:

• Empiric doxycycline therapy ASAP - same treatment of choice you use for Lyme

• Public health laboratory testing (reporting reportable illnesses is part of your management plan)

• Serum antibody immunoglobulin G

• Blood or skin biopsy polymerase chain reaction (PCR)

A study tip for this one: Prophylaxis will not prevent infection, but don’t wait for testing to treat. Think of RSMF early and you could help your patient avoid a serious outcome: if you’re asked about complications on a MCQ-SAMP, be aware that 57% of patients with RSMF needed admission (e.g. renal, respiratory, liver, or brain failure a.k.a. encephalitis).

Study hard and hope to see some of you at The Review Course! Register here.

Source

Photo by Jerry Kirkhart from Los Osos, Calif. - American Dog Tick (Dermacentor variabilis), CC BY 2.0