Everybody knows somebody- that knows somebody-that has been affected by Lyme disease. The symptoms in humans are plenty: severe headaches, joint pain, muscle aches, heart palpitations, dizziness, and fatigue, to name a few—it can be very debilitating and long-lasting. 

But what about dogs? Lyme disease in dogs is complex and often misunderstood. While it is caused by the same bacterium, Borrelia burgdorferi, dogs respond to the infection differently than humans do.

The Ixodes Tick Life Cycle and Lyme Transmission

The Ixodes scapularis tick, commonly known as the deer tick, has a two-year life cycle with three stages: larva, nymph, and adult.

1) Larvae hatch and feed on small mammals, particularly white-footed mice, which serve as reservoirs for Borrelia burgdorferi.

2)  After a year, larvae molt into nymphs, which take another blood meal—this is when dogs can become infected.

3)  Nymphs then mature into adult ticks, which prefer larger hosts like deer and dogs.

Since Lyme transmission occurs when infected ticks feed for at least 24–48 hours, prompt tick removal reduces infection risk. However, some studies suggest transmission can occur in less than 24 hours in rare cases.

Interestingly, Lyme disease is more common in the Northeast (including Pennsylvania)  because ticks there primarily feed on rodents. In contrast, in the Southwest, larvae tend to feed on reptiles, which have natural anti-Borrelia factors, reducing the bacteria’s survival.

Understanding the 4DX Test and a Positive Lyme Result

Most dogs get an annual 4DX test, screening for heartworm, anaplasmosis, ehrlichiosis, and Lyme disease. A positive Lyme test only confirms exposure, not active disease.

Unlike humans—where 70–80% of exposed individuals develop symptoms—only about 5% of infected dogs actually show signs of illness. Dogs appear to be more adapted to Borrelia burgdorferi, meaning a positive test does not necessarily mean the dog is sick.

What Happens if My Dog Tests Positive?

There is no universal consensus on how to handle asymptomatic, Lyme-positive dogs. The 2018 ACVIM (American College of Veterinary Internal Medicine) consensus suggests:

• No automatic antibiotic treatment for asymptomatic dogs to avoid unnecessary antibiotic use.

 • Monitoring urine protein-to-creatinine ratios yearly to catch early signs of Lyme nephritis, a severe but rare kidney complication.

Some veterinarians still use Lyme C6 quantitative testing to decide whether to treat, but there is no proven correlation between antibody levels and disease severity. Additionally, Lyme C6 levels decline naturally over six months, even without treatment, because Borrelia evades the immune system by changing surface proteins. So, a drop in Lyme C6 antibodies does not necessarily mean antibiotics worked—it could have happened on its own.

Even with antibiotic treatment, Borrelia is never fully eliminated from the body, as some bacteria can persist in connective tissue.

Signs of Lyme Disease in Dogs & The Role of Co-Infections

When Lyme disease does cause illness in dogs, the most common symptoms are:

• Polyarthritis (shifting-leg lameness due to joint inflammation)

• Lyme nephritis (a serious, immune-mediated kidney disease)

Symptoms usually appear 2–5 months after infection. However, co-infections complicate diagnosis. Ticks often carry multiple pathogens, like Anaplasma and Ehrlichia, which can cause fever, lethargy, and joint pain. If a Lyme-positive dog has a fever, another tick-borne infection could be the real culprit. Some co-infections, like Babesia, are not routinely tested for.

The Lyme Vaccine Debate: Is It Worth It?

The 2018 ACVIM consensus showed disagreement on Lyme vaccination. Out of six experts, only three recommended vaccination, while others expressed concerns. The main concern? A theoretical risk that high levels of Lyme antibodies might contribute to Lyme nephritis. However, this has not been definitively proven. 

New Vaccine Technology

Modern recombinant vaccines now target Borrelia inside the tick’s gut. When a vaccinated dog is bitten, the tick ingests antibodies that prevent Borrelia from moving to the salivary glands, stopping transmission before it reaches the dog. These vaccines are less reactive than older whole-bacteria vaccines.

Tick Prevention: Your Dog’s Best Defense

While vaccines help, veterinary-approved tick preventatives are still the best way to prevent Lyme disease and other tick-borne illnesses. Whether your dog is vaccinated or not, consistent tick prevention—oral or topical treatments—should be a priority year-round.

Every Veterinarian Has a Different Approach—And That’s Okay

I always tell my clients that there is no single “correct” way to manage Lyme disease. While some veterinarians use Lyme C6 levels to decide on treatment and others prescribe antibiotics to asymptomatic dogs, we can ALL agree on monitoring urine protein levels to detect kidney issues early.

Since Lyme disease is not fully understood, different approaches exist, and none are necessarily wrong. The key is open communication between pet owners and veterinarians to decide the best plan for each individual dog.

By  Dr. Caroline Simard-Swimmer
Medical Director & Co-FounderPets After Dark