Birds Spread Lyme Disease Ticks Across Canada

Millions of ticks are carried north each spring
Songbirds can transport ticks hundreds of kilometers
New Lyme disease risk areas may form faster than expected

“We estimate that migratory birds disperse 50 million to 175 million Ixodes scapularis (deer) ticks across Canada each spring,” wrote Ogden and colleagues, highlighting the significant role birds may play in expanding Lyme disease risk.

How Birds Spread Lyme Disease Ticks

A study by Scott and colleagues found that migratory songbirds can carry ticks into “new areas hundreds of kilometers away from their original source,” including regions beyond the current climate range for tick survival.

This helps explain why Lyme disease risk continues to expand into new areas—a pattern also discussed in our Lyme disease risk increasing overview.

Evidence from Nesting Songbirds

Researchers studied nesting songbirds, which stay close to their nests during the summer months. This allowed investigators to determine whether local tick populations had become established.

To confirm an established population, researchers needed to identify at least 6 ticks from a specific area and detect at least 2 of the 3 life stages (larva, nymph, adult).

The results were striking. Investigators found 63 black-legged nymphal ticks and 1 larval tick. In one case, both larval and nymphal ticks were collected from a single bird within the same year—evidence of an established local population.

Infected Ticks and Lyme Disease Risk

Nearly half of the ticks collected were infected with Borrelia burgdorferi, the bacterium responsible for Lyme disease. Specifically, 14 (42%) of 33 nymphal ticks tested positive.

This level of infection increases the risk for individuals living in or traveling through these newly affected regions.

Why This Matters

Tick exposure is no longer limited to historically recognized endemic areas. As birds transport ticks into new environments, individuals may be at risk even in regions previously considered low risk—highlighting the importance of awareness and prevention strategies outlined in our Lyme disease prevention guide.

Public health efforts must adapt to these changing patterns, and clinicians should consider Lyme disease even in areas where it was previously uncommon.

Key Recommendations

• Take precautions to avoid tick bites and perform daily tick checks
• Seek medical attention if bitten or if symptoms of Lyme disease develop
• Clinicians should maintain a high index of suspicion in symptomatic patients, even outside traditional endemic areas

Dr. Daniel Cameron, MD, MPH
Lyme disease clinician with over 30 years of experience and past president of ILADS.

Symptoms • Testing • Coinfections • Recovery • Pediatric • Prevention