What is Lyme Disease?

Lyme disease is caused by the spirochete bacterium Borrelia burgdorferi, transmitted to dogs through the bite of infected black-legged ticks (also known as deer ticks, Ixodes scapularis in eastern North America and Ixodes pacificus on the west coast). It is the most common tick-borne disease in North America and is expanding its geographic range as tick populations grow due to climate change and shifting wildlife patterns.

In Canada, Lyme disease has become increasingly prevalent, particularly in southern Ontario, Quebec, Nova Scotia, New Brunswick, and Manitoba. The number of affected regions continues to grow each year.

Symptoms

Many dogs infected with Borrelia burgdorferi (estimated 90–95%) never show clinical signs. In those that do develop illness, symptoms typically appear 2–5 months after a tick bite:

  • Lameness: Shifting leg lameness (alternating between legs), often episodic
  • Swollen, painful joints
  • Fever
  • Lethargy and depression
  • Loss of appetite
  • Swollen lymph nodes

Lyme Nephritis

The most serious complication is Lyme nephritis — a severe, often fatal kidney disease. It is more common in certain breeds (Labrador Retrievers, Golden Retrievers, Shetland Sheepdogs, Bernese Mountain Dogs). Signs include:

  • Vomiting
  • Weight loss
  • Increased thirst and urination
  • Edema (fluid buildup)
  • Kidney failure

Transmission

Lyme disease transmission requires a tick to be attached and feeding for at least 24–48 hours. This is why prompt tick removal is so effective at preventing infection. Ticks acquire the bacteria by feeding on infected wildlife (primarily white-footed mice and other small rodents).

Lyme disease is not transmitted directly from dog to dog or from dog to human. However, ticks on your dog can detach and bite humans, so a dog with ticks increases the household's risk.

Diagnosis

  • SNAP 4Dx test: An in-clinic blood test that screens for antibodies to Borrelia burgdorferi (also tests for heartworm, Ehrlichia, and Anaplasma)
  • Quantitative C6 antibody test: Measures the level of specific antibodies to help determine if infection is active
  • A positive test alone does not mean a dog needs treatment — clinical signs must be present

Vaccination

The Lyme vaccine is a non-core vaccine recommended for dogs in areas where ticks carrying Borrelia burgdorferi are prevalent.

Vaccination Schedule

  • Puppies: Two doses starting at 12 weeks, 2–4 weeks apart
  • Adult dogs: Two initial doses 2–4 weeks apart
  • Boosters: Annually, ideally administered before tick season begins

Important Notes

  • The vaccine does not protect against all strains of Borrelia
  • Vaccination should always be combined with tick prevention (topical, oral, or collar)
  • The vaccine is not recommended for dogs in areas without significant tick exposure

Tick Prevention

Vaccination alone is not sufficient. A comprehensive approach includes:

  • Tick preventatives: Monthly oral (e.g., NexGard, Simparica) or topical products year-round in endemic areas
  • Tick checks: Examine your dog after every outdoor excursion, especially in wooded or grassy areas
  • Prompt removal: Use fine-tipped tweezers to remove ticks as soon as possible
  • Yard management: Keep grass short, remove leaf litter, create tick-free zones

Treatment

Dogs with clinical Lyme disease are treated with:

  • Doxycycline for 4–6 weeks (the antibiotic of choice)
  • Anti-inflammatory medication for joint pain
  • Supportive care for kidney involvement if needed

Most dogs respond well to treatment within 24–48 hours, though the antibodies may persist for years.

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