Lyme disease can be serious for dogs, but most infected dogs never get sick. Only 5% to 10% of dogs infected with the Lyme-causing bacteria develop symptoms. The majority carry the infection without any visible signs of illness. When symptoms do appear, though, they can range from painful joint inflammation to life-threatening kidney damage.
Most Infected Dogs Stay Healthy
This is the most reassuring part of canine Lyme disease: the vast majority of dogs who test positive for exposure will appear completely normal. Their immune systems keep the bacteria in check without any intervention. This is a sharp contrast to humans, where an estimated 90% of infected people develop illness.
A positive test result on its own doesn’t mean your dog is sick or will become sick. Many veterinarians discover Lyme exposure during routine annual screening, and the dog has shown zero symptoms. Whether to treat an asymptomatic dog is a judgment call your vet will make based on additional lab work, particularly checking for signs of kidney involvement.
What Symptoms Look Like
For the 5% to 10% of dogs that do develop clinical Lyme disease, the hallmark symptom is sudden, painful lameness. Once in the bloodstream, the bacteria travel throughout the body and tend to settle in the joints or kidneys. Dogs with active Lyme disease typically show swollen joints, fever, and a distinctive “shifting leg” lameness where the pain moves from one leg to another over days or weeks.
This lameness can be confusing for owners because it sometimes disappears on its own, only to return weeks or months later. Other signs include lethargy, loss of appetite, and general stiffness. Some dogs walk as though they’re on eggshells, reluctant to put full weight on any limb.
The Serious Complication: Kidney Damage
The most dangerous form of Lyme disease in dogs is a kidney condition sometimes called Lyme nephritis. In these cases, the bacteria or the immune response they trigger causes progressive kidney failure. Symptoms include vomiting, increased thirst and urination, weight loss, and fluid buildup in the legs or abdomen. Lyme nephritis is relatively rare, but it carries a poor prognosis and can be fatal. Certain breeds, including Labrador Retrievers, Golden Retrievers, and Bernese Mountain Dogs, appear to be at higher risk for this complication, though it can affect any breed.
How It’s Diagnosed
Most veterinary clinics use a quick in-house blood test that detects antibodies to a specific protein called C6, which the Lyme bacteria produce only inside a living host. This is important because the C6 test can distinguish between a dog that’s actually been infected and one that simply received a Lyme vaccine. A positive screening test is often followed up with more detailed lab work to determine whether the infection is early or chronic and whether the kidneys are affected. Cornell University’s veterinary diagnostic lab developed a multiplex assay that can identify the stage of infection and vaccination status simultaneously, giving vets a more complete picture than a single-marker test alone.
Treatment and Recovery
Dogs with active Lyme disease are treated with a course of antibiotics, typically lasting about four weeks. Most dogs with joint symptoms respond quickly, often improving within days of starting treatment. That said, a significant number of affected dogs don’t fully recover. Some experience chronic, lifelong joint pain from the damage the bacteria caused before treatment began. Early detection and prompt treatment give your dog the best chance of a full recovery, which is one reason annual screening is valuable even in dogs that seem perfectly fine.
Where the Risk Is Highest
Lyme disease is transmitted by blacklegged ticks (also called deer ticks), and your dog’s risk depends heavily on where you live. The Upper Midwest and Northeast remain the highest-risk regions in the United States. But the geographic range is expanding steadily. Ohio, Kentucky, West Virginia, and parts of northern Tennessee and North Carolina are projected to see some of the greatest increases in Lyme risk. The spread is also pushing westward from Minnesota into North Dakota, eastern Montana, and northern South Dakota, and northward into previously unaffected areas of Canada.
If you’ve moved to or travel with your dog in any of these regions, Lyme prevention matters even if it wasn’t on your radar before. Iowa’s southeast region, Indiana, Illinois, and Michigan are all seeing elevated risk compared to historical patterns.
Prevention: Ticks, Vaccines, and Daily Checks
Tick prevention products are your first line of defense. Oral or topical treatments that kill ticks before they can transmit the bacteria are widely available and effective. Removing ticks promptly also helps, since the bacteria generally need the tick to be attached for at least 24 to 48 hours before transmission occurs. A daily tick check after walks in wooded or grassy areas gives you a realistic window to find and remove ticks before they become a problem.
A Lyme vaccine is available for dogs. In a field study conducted in a high-risk area of Connecticut, vaccinated dogs had an infection rate of 25% compared to 63% in unvaccinated dogs, translating to roughly 60% efficacy. That’s meaningful protection but far from complete, which is why vaccination works best as one layer in a broader prevention strategy rather than a standalone solution. The vaccine requires an initial two-dose series followed by annual boosters. It’s most commonly recommended for dogs living in or frequently visiting endemic areas.
For dogs in low-risk regions who rarely encounter ticks, the vaccine may not be necessary. Your vet can help weigh the benefits based on your dog’s lifestyle and location.