Lyme Disease Strains: Why Symptoms and Treatment Vary

Lyme disease strains vary in their ability to cause illness—and this may help explain why some patients recover quickly while others develop more complex disease.

Researchers have identified multiple genotypes of Borrelia burgdorferi, each expressing different outer surface proteins that influence virulence. :contentReference[oaicite:0]{index=0}

Clinical insight: the strain of Lyme disease may affect how severe the infection becomes.

Three Types of Lyme Strains

According to Seinost and colleagues, Borrelia burgdorferi strains can be grouped into three categories:

• Strains commonly found in ticks but rarely causing human disease
• Strains causing only localized infection at the bite site
• Strains capable of spreading throughout the body and causing systemic illness

Key distinction: not every exposure leads to the same type of infection.

Why Strain Diversity Matters

In a study published in PLoS Pathogens, researchers found that:

• 70% of infected deer ticks carried multiple strains of Lyme bacteria
• A single tick bite may expose a person to several different strains

Clinical implication: mixed infections may contribute to variability in symptoms and outcomes.

Study finds 70% of infected ticks carry multiple Lyme strains.

More Strains, More Complexity

The genetic diversity of Lyme bacteria appears to be increasing.

This evolution is driven by interactions with natural hosts, including rodents and birds.

Result: a wider range of strains with differing virulence profiles.

These complex interactions may lead to:

• More varied clinical presentations
• Differences in immune response
• Challenges in treatment response

What This Means for Patients

Not all Lyme disease behaves the same way.

Some patients experience mild, localized illness.

Others develop:

• Disseminated infection
• Neurologic involvement
• Persistent or relapsing symptoms

Clinical reality: strain differences may help explain why outcomes vary.

Could Strains Affect Treatment Response?

Strain diversity raises important questions about treatment.

Possibility: different strains—or combinations of strains—may respond differently to therapy.

This may contribute to:

• Incomplete symptom resolution
• Relapsing symptoms
• Variability in treatment outcomes

Clinical takeaway: treatment responses may reflect underlying biological differences—not just treatment choices.

Why This Research Matters

Understanding Lyme disease strains provides insight into:

• Why some infections remain localized
• Why others disseminate
• Why symptoms and recovery differ between patients

Key point: Lyme disease is not a single uniform infection.

Clinical Takeaway

Lyme disease strains vary in virulence, and this diversity may influence symptom severity, disease progression, and treatment response.

Recognizing this variability can help explain why patients experience Lyme disease so differently.

Key question: Could differences in bacterial strains help explain why some patients recover quickly while others do not?

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