Dogs get Lyme disease from the bite of an infected tick, specifically a black-legged tick (also called a deer tick). The tick must be attached and feeding for at least 24 to 48 hours before the bacteria that cause Lyme disease can pass into a dog’s bloodstream. That delay is the single most important fact for dog owners to understand, because it means prompt tick removal can prevent infection entirely.
How the Bacteria Get From Tick to Dog
The bacterium responsible for Lyme disease lives in the gut of infected black-legged ticks. When a tick latches onto your dog and begins feeding, the bacteria don’t transfer immediately. Instead, as the tick feeds over many hours, the bacteria migrate from its gut up into its salivary glands and then into your dog through the bite wound. This process takes a minimum of 24 hours, and most sources cite 24 to 48 hours as the window before transmission occurs.
This is why a tick crawling on your dog’s fur isn’t a risk. Only a tick that has burrowed into the skin and stayed attached long enough to complete a full feeding cycle can deliver the bacteria. A tick you find and remove within the first day is unlikely to have transmitted anything.
Which Ticks Carry Lyme Disease
Only two tick species in North America transmit Lyme disease to dogs. In the eastern half of the continent, the culprit is the black-legged tick (sometimes called the deer tick). In western states, a close relative, the western black-legged tick, fills the same role. Other common ticks, like the brown dog tick or the American dog tick, do not carry the Lyme bacterium.
Both species are “three-host” ticks, meaning they feed on a different animal at each life stage: larva, nymph, and adult. A larva or nymph picks up the bacteria from an infected animal (often a mouse or other small rodent), then carries that infection through its next life stage. Nymphs and adults are the stages most likely to transmit Lyme to your dog. Adults are especially relevant for dogs because they are most active during cooler months, from fall through early spring, when many dog owners aren’t thinking about ticks at all.
Where the Risk Is Highest
The Upper Midwest and Northeast remain the highest-risk regions for canine Lyme disease in the United States, but the map is expanding. According to the Companion Animal Parasite Council’s 2026 forecast, Lyme risk is growing significantly across Indiana, Illinois, Michigan, and Ohio. States like Kentucky, West Virginia, and parts of northern Tennessee and North Carolina are projected to see some of the greatest increases compared to historical patterns.
Westward spread is also underway. Elevated risk now extends into North Dakota, eastern Montana, and northern South Dakota, pushed by the spread of infected tick populations out of heavily endemic Minnesota. Iowa, particularly its southeastern region, is expected to remain higher than normal. Black-legged tick populations are also moving north into previously unaffected areas of Canada. If you live in or travel with your dog to any of these regions, Lyme prevention is worth taking seriously year-round.
What Lyme Disease Looks Like in Dogs
Most dogs infected with the Lyme bacterium never show symptoms. Estimates vary, but only a small percentage of exposed dogs develop clinical illness. When symptoms do appear, they typically emerge weeks to months after the initial tick bite, making it difficult to connect the illness to a specific exposure.
The hallmark sign is lameness that may shift from one leg to another over days. Your dog might limp on a front leg one day and a back leg a few days later. Swollen, warm joints are common, along with fever, lethargy, and reduced appetite. Some dogs become noticeably stiff or reluctant to move.
A rare but serious complication is kidney disease caused by the Lyme infection. This can develop weeks to months after the initial infection and may progress quickly. Signs include increased thirst, vomiting, weight loss, and swelling in the legs or abdomen. Certain breeds, including Labrador Retrievers and Golden Retrievers, appear to be more susceptible to this kidney complication.
How Vets Test for Lyme Disease
Most veterinary clinics use an in-office blood test that screens for antibodies to the Lyme bacterium alongside a few other tick-borne infections. The most widely used version of this test has a diagnostic accuracy of about 97% for Lyme disease, with 98.5% sensitivity, meaning it catches nearly all true infections, and 95.7% specificity, meaning false positives are uncommon.
A positive screening test tells your vet that your dog has been exposed, but it doesn’t necessarily mean your dog is sick. Many dogs test positive without ever developing symptoms. If the screening is positive, your vet will typically run additional bloodwork and a urine test to check for kidney involvement and determine whether treatment is needed. A more specific antibody level test can help track whether an active infection is responding to treatment over time.
Your Dog Can’t Give You Lyme Disease Directly
Dogs cannot transmit Lyme disease to people through contact, saliva, or shared space. The bacteria can only enter a new host through a tick bite. However, your dog can carry infected ticks into your home or yard, and those ticks can then attach to you or your family members. In that sense, a dog with frequent tick exposure increases your household’s risk indirectly. This is one more reason regular tick checks after outdoor time matter for both you and your dog.
Prevention: Tick Control and Vaccination
The most effective way to prevent Lyme disease in dogs is to kill ticks before they’ve been attached long enough to transmit the bacteria. Modern oral flea and tick preventatives work by killing ticks after they bite, typically within hours. Because transmission requires at least 24 hours of attachment, these products can eliminate the tick before the bacteria ever reach your dog’s bloodstream. Year-round use is especially important for black-legged ticks, since adults feed during fall and winter when many owners stop using preventatives.
Daily tick checks are a powerful backup. After walks in wooded or grassy areas, run your hands over your dog’s entire body, paying attention to the ears, armpits, groin, and between the toes. Removing a tick within the first 24 hours dramatically reduces the chance of infection.
A Lyme vaccine is also available. Studies suggest it prevents infection or illness in roughly 60% to 86% of vaccinated dogs, which is helpful but not airtight. The vaccine requires annual boosters (some vets recommend every six months in high-risk areas) and works best as a complement to tick prevention rather than a replacement for it. It’s generally recommended for dogs living in or frequently traveling to areas where Lyme is common.