Babesiosis

Babesiosis is closer to malaria than to most other tick-borne illnesses — the pathogen is a single-celled parasite that invades and breaks down red blood cells. Canadian cases are still rare, but the disease is showing up wherever blacklegged ticks become established.

Transmission typically requires 36–48 hours of attachment — somewhat longer than for Lyme. Same-day removal is highly protective.

Symptoms appear one to four weeks after a bite, sometimes longer. Many healthy adults have mild or no symptoms. When it does cause illness:

• Fever, often with drenching sweats and shaking chills
• Fatigue
• Muscle and joint aches
• Headache
• Loss of appetite
• In severe cases: dark urine, yellowing of the skin (hemolytic anemia), shortness of breath

Because babesiosis shares geography with Lyme, it’s often diagnosed alongside it — symptoms overlap. If a presumed-Lyme illness doesn’t respond to standard antibiotics, babesiosis is a common reason why.

This week:drenching sweats and shaking chills in the weeks after a tick bite, especially if standard Lyme treatment doesn’t resolve the illness.

Emergency room: severe shortness of breath, very dark urine, jaundice, confusion, or any signs of organ failure — particularly in older patients or anyone without a spleen.

Mild babesiosis is treated with a combination of atovaquone and azithromycin. Severe cases — high parasite burden, organ involvement, immunocompromised patients — may require clindamycin with quinine, and occasionally exchange transfusion in hospital. Diagnosis is confirmed by blood smear or PCR.

The same blacklegged-tick footprint as Lyme: southern Ontario, southern Quebec, Nova Scotia, and New Brunswick, with emerging cases elsewhere. Canadian babesiosis case counts are still low compared to Lyme, but PHAC tracks it as a notifiable disease.

Public Health Agency of Canada (babesiosis health-professional guidance).