Ehrlichiosis

Ehrlichiosis is a close cousin of anaplasmosis. Both are bacteria that infect white blood cells, cause a similar illness, and respond to the same antibiotic. The difference is the tick: ehrlichiosis comes mainly from the Lone Star tick, which is established in a small part of southwestern Ontario and turns up further afield on migratory birds.

Transmission typically requires several hours of attachment. Same-day tick checks and prompt removal substantially lower the risk.

1–2 weeks after a bite:

• Fever
• Severe headache
• Fatigue
• Muscle aches
• Sometimes nausea or vomiting
• A rash in about a third of cases (small spots, often on the trunk or limbs)

Bloodwork shows low platelets and elevated liver enzymes, much like anaplasmosis. Severe untreated cases can progress to organ involvement, especially in older or immunocompromised patients.

This week: a flu-like illness with high fever and severe headache, 1–2 weeks after a tick bite in southern Ontario. Mention the Lone Star tick if you saw or saved it (the adult female has a single bright white dot on her back).

Emergency room: confusion, severe shortness of breath, signs of shock, or any neurological symptoms.

Ehrlichiosis is treated with doxycycline. Most patients respond within 48 hours of starting antibiotics. As with anaplasmosis, treatment shouldn’t wait for lab confirmation when the clinical picture and exposure history fit.

Cases are rare and concentrated in southwestern Ontario, where the Lone Star tick is getting established. Isolated reports turn up elsewhere when Lone Stars arrive on migratory birds. The Public Health Agency of Canada tracks the tick’s spread closely. Expect both the tick and this illness to spread over the next decade.

Public Health Agency of Canada; Ontario provincial surveillance reports.