Lyme Disease in Dogs: Tick-Borne Bacterial Infection Guide

Lyme disease (borreliosis) is one of the most common tick-borne infectious diseases in the Northern Hemisphere. It is caused by the spiral-shaped bacterium Borrelia burgdorferi (and in Europe, also B. afzelii and B. garinii) and is transmitted to dogs through the bite of infected ticks — primarily Ixodes scapularis (the black-legged or deer tick) in North America and Ixodes ricinus (the castor bean tick) in Europe and the UK.

"What many owners don't realise is that a tick must be attached for at least 24-48 hours before Borrelia transmission occurs. That's because the bacteria live in the tick's gut and need time to migrate to the salivary glands. This gives us a critical window — daily tick checks and prompt removal can prevent Lyme disease entirely." — Dr. Sarah Chen, DVM

The transmission cycle of Lyme disease involves several stages:

• Reservoir hosts — white-footed mice, voles, and other small mammals carry Borrelia without becoming ill. These animals maintain the bacteria in the environment
• Tick vectors — larval ticks acquire the bacteria when feeding on infected rodents. The bacteria persist through the nymph and adult stages
• Transmission to dogs — nymphal and adult ticks attach to dogs during outdoor activities. After 24-48 hours of feeding, the bacteria migrate from the tick's midgut to its salivary glands and are injected into the dog's skin
• Dissemination — once in the skin, Borrelia organisms spread through connective tissue and can reach the joints, kidneys, nervous system, and heart

Lyme disease has a distinct geographic distribution, with highest risk in the northeastern and upper midwestern United States, and across much of the UK and northern Europe. However, the range of Ixodes ticks is expanding due to climate change, and cases are now reported in areas previously considered low-risk. Comprehensive tick prevention is essential for all dogs in endemic areas.

One of the most striking features of canine Lyme disease is that the majority of infected dogs — an estimated 90-95% — never show clinical signs. They become seropositive (develop antibodies) but remain healthy. However, the 5-10% that do develop symptoms can become seriously ill, and the most feared complication, Lyme nephritis, can be fatal.

Classic Lyme Disease Symptoms

When symptoms do appear, they typically develop 2-5 months after the tick bite:

• Shifting-leg lameness — the hallmark symptom. Dogs develop sudden lameness in one leg that may resolve within days, only to appear in a different leg. This occurs because the bacteria cause inflammation in multiple joints (polyarthritis)
• Joint swelling and pain — affected joints may be visibly swollen, warm to the touch, and painful on manipulation. Dogs may yelp when rising, refuse to jump, or be reluctant to climb stairs
• Fever — temperatures of 39.5-40.5°C (103-105°F) may accompany acute episodes
• Lethargy and decreased appetite — dogs may seem depressed, less playful, and uninterested in food
• Enlarged lymph nodes — the lymph nodes closest to the site of the tick bite may be palpably enlarged

Lyme Nephritis: The Most Serious Complication

Lyme nephritis is a potentially fatal kidney disease that occurs in a small percentage of Lyme-positive dogs. Certain breeds are predisposed, particularly Labrador Retrievers, Golden Retrievers, and Bernese Mountain Dogs. The condition involves:

• Immune-complex glomerulonephritis — antibody-antigen complexes deposit in the kidney's filtering units, causing progressive destruction
• Protein-losing nephropathy — massive protein loss in the urine leads to low blood protein, fluid accumulation (oedema), and eventually kidney failure
• Symptoms — vomiting, weight loss, increased thirst and urination, decreased appetite, swollen limbs due to fluid retention

Lyme nephritis carries a poor prognosis, with many affected dogs progressing to end-stage kidney failure despite treatment. This is one of the strongest arguments for aggressive tick prevention in high-risk breeds. If your dog has been diagnosed with Lyme disease, regular urine testing for protein can catch kidney involvement early.

Diagnosing Lyme disease in dogs requires careful interpretation of test results alongside clinical signs, because many exposed dogs test positive without ever being ill. Your vet will use a combination of serological testing, clinical assessment, and additional diagnostics to determine whether treatment is needed.

SNAP 4Dx Test (In-Clinic Screening)

The most common first-line test is the SNAP 4Dx or similar in-clinic ELISA that screens for antibodies against four tick-borne diseases simultaneously: Lyme disease, anaplasmosis, ehrlichiosis, and heartworm. This test:

• Detects C6 antibody — a specific antibody against the C6 peptide of Borrelia burgdorferi. A positive result means the dog has been exposed to (and infected by) the bacterium
• Results in 10 minutes — making it ideal for annual screening or when Lyme disease is suspected
• Does not distinguish past from current infection — antibodies persist for months to years after exposure, regardless of whether active disease is present

Quantitative C6 Antibody Test (Lyme Quant C6)

When the screening test is positive, your vet may send blood for a quantitative C6 antibody level:

• Levels above 30 U/mL — generally support active or recent infection and may warrant treatment, especially if combined with clinical signs
• Monitoring response — a significant drop in C6 levels (50% or greater) 6 months after treatment suggests successful clearance of active infection

Complete Blood Work and Urinalysis

These are essential in every Lyme-positive dog to assess organ involvement:

• Kidney values — BUN and creatinine elevations suggest Lyme nephritis
• Urine protein-to-creatinine ratio (UPC) — the most sensitive early marker of Lyme nephritis. All Lyme-positive dogs should have this test, even without symptoms
• Complete blood count — may show inflammatory changes

Joint Fluid Analysis

For dogs with significant lameness, arthrocentesis (sampling joint fluid) may reveal the non-erosive inflammatory arthritis characteristic of Lyme disease — elevated white blood cells without joint destruction. PCR testing of joint fluid can sometimes detect Borrelia DNA, though sensitivity is variable.

Annual screening during routine vet visits is recommended for all dogs in Lyme-endemic areas, even those on tick prevention, to catch asymptomatic infections early.

Not every Lyme-positive dog requires treatment. The decision to treat depends on the presence of clinical signs, antibody levels, and kidney function. When treatment is indicated, the primary approach is antibiotic therapy.

When to Treat

Current veterinary consensus recommends treatment for:

• Dogs with clinical signs — lameness, fever, joint swelling, or other symptoms consistent with Lyme disease
• Dogs with high C6 levels — quantitative C6 above 30 U/mL, even without symptoms, may benefit from treatment to prevent future complications
• Dogs with proteinuria — any Lyme-positive dog with elevated urine protein needs treatment to slow or prevent Lyme nephritis

Lyme-positive dogs without symptoms, with low C6 levels, and with normal urinalysis may be monitored rather than treated, with repeat testing in 6 months.

Antibiotic Treatment

• Doxycycline — the antibiotic of choice for canine Lyme disease. Dose: 10 mg/kg orally every 12-24 hours for 30 days. Doxycycline is preferred because it is also effective against other tick-borne co-infections (Anaplasma, Ehrlichia) that may be present simultaneously
• Amoxicillin — an alternative for dogs that cannot tolerate doxycycline (e.g., puppies under 6 months, dogs with gastrointestinal sensitivity). Dose: 20 mg/kg orally every 8-12 hours for 30 days
• Response to treatment — dogs with Lyme arthritis typically show dramatic improvement within 24-48 hours of starting antibiotics. This rapid response is itself considered supportive of the diagnosis

Managing Lyme Nephritis

Treatment for Lyme nephritis is more complex and carries a guarded prognosis:

• Antibiotics — doxycycline to address the underlying infection
• Immunosuppressive therapy — mycophenolate or azathioprine to reduce the immune-mediated kidney damage
• ACE inhibitors — enalapril or benazepril to reduce protein loss through the kidneys
• Supportive care — fluid therapy, renal diet, phosphate binders, and anti-hypertensives as kidney function declines
• Ongoing monitoring — frequent blood work and urinalysis to track kidney function

Even with aggressive treatment, Lyme nephritis often progresses. This underscores the critical importance of prevention over treatment for this disease.

Preventing Lyme disease relies on a three-pronged strategy: keeping ticks off your dog, vaccination where appropriate, and reducing tick habitat exposure. Given the difficulty of treating Lyme nephritis and the limitations of antibiotics in fully clearing Borrelia from the body, prevention is unquestionably the best approach.

Tick Prevention Products

Year-round tick prevention is recommended for all dogs in endemic areas. Effective options include:

• Isoxazoline oral preventives — fluralaner (Bravecto), afoxolaner (NexGard), sarolaner (Simparica), lotilaner (Credelio). These are highly effective, killing ticks within 12-24 hours of attachment — often before Borrelia transmission can occur
• Topical preventives — fipronil-based products (Frontline) and permethrin spot-ons provide repellent and acaricidal action
• Tick collars — seresto collars release imidacloprid and flumethrin over 8 months, providing long-lasting protection

For detailed guidance on choosing the right product, see our comprehensive flea and tick prevention guide.

Lyme Disease Vaccination

Several Lyme vaccines are available for dogs:

• OspA-based vaccines — these generate antibodies that kill Borrelia inside the tick during feeding, preventing transmission
• Recombinant OspA vaccines — newer formulations with fewer side effects
• Vaccination schedule — initial vaccine at 12 weeks of age, booster 2-4 weeks later, then annual boosters. Best given before tick season begins
• Who should be vaccinated — dogs in high-risk areas, outdoor dogs, hunting dogs, and predisposed breeds (Labradors, Goldens, Bernese). The vaccine is non-core and should be discussed with your vet based on regional risk

Daily Tick Checks

Even with preventives, daily tick checks remain important:

• Check after every outdoor excursion — run your hands over your dog's entire body, paying special attention to the ears, head, neck, armpits, groin, and between toes
• Remove ticks promptly — use fine-tipped tweezers or a tick removal tool. Grasp the tick as close to the skin as possible and pull steadily upward without twisting. Save the tick for identification if possible
• Remember the 24-48 hour window — prompt removal before this window closes prevents Borrelia transmission in most cases

Keep a pet first aid kit with tick removal tools readily available, especially during hiking or camping trips.

If your dog has tested positive for Lyme disease — whether or not they've shown symptoms — ongoing monitoring is an important part of responsible pet ownership. Borrelia organisms can persist in tissue even after antibiotic treatment, and the risk of future complications, particularly kidney disease, warrants long-term vigilance.

Monitoring Schedule

For Lyme-positive dogs, most veterinary internists recommend:

• Every 6 months — complete urinalysis including urine protein-to-creatinine ratio (UPC). This is the most important monitoring test, as rising urinary protein is often the earliest sign of Lyme nephritis
• Annually — complete blood work including kidney values, liver enzymes, and CBC
• Annually — quantitative C6 antibody levels to track whether the immune response is declining (suggestive of clearance) or rising (suggestive of re-infection or persistent infection)
• As needed — any new lameness, joint swelling, or change in urination patterns should prompt an immediate veterinary visit

Lifestyle Considerations

A Lyme-positive dog can live a completely normal, active life in most cases:

• Continue regular exercise — unless your dog is experiencing active joint symptoms, there is no need to restrict activity
• Maintain strict tick prevention — re-infection with additional Borrelia strains can worsen the immune response and increase kidney risk
• Support joint health — omega-3 fatty acids, glucosamine, and chondroitin supplements may help reduce joint inflammation
• Kidney-supportive nutrition — for dogs with any sign of proteinuria, a moderate-protein, low-phosphorus diet may be recommended

Can Humans Catch Lyme from Dogs?

No — Lyme disease is not transmitted directly from dogs to humans. However, a Lyme-positive dog is a sentinel: it tells you that infected ticks are present in your environment. If your dog has Lyme disease:

• You and your family are also at risk from tick bites in the same area
• Perform daily tick checks on all family members, especially children
• Use insect repellent containing DEET or picaridin during outdoor activities
• Wear long sleeves and trousers in tick-prone areas and tuck trousers into socks

Maintaining your dog's full preventive care schedule — including tick prevention, vaccination, and regular screening — is the best way to protect both your dog and your family from tick-borne diseases.