Lyme Disease (Lyme Borreliosis) in Dogs

Lyme disease is caused by Borrelia burgdorferi bacteria and is spread through the bite of infected ticks. It affects dogs, horses, cats, and people. Several tick species can carry the disease, but most infections are caused by the deer tick (black-legged tick).

Ticks don't cause Lyme disease directly, but they spread the bacteria that cause it. Ticks prefer to bite rodents like mice and voles, as well as deer, but they also bite dogs and people. To spread the disease, the tick usually needs to be attached to an animal or person for 1–2 days, so removing ticks quickly is the safest way to prevent the spread of disease. The highest-risk times are spring and autumn, when ticks are most active.

In the United States, Lyme disease has been reported in all states, but it is most common in the Northeast (especially New England), the upper Midwest, and along the Pacific Coast. Up to half of all ticks are infected in some areas. The disease is named after Lyme, Connecticut, where it was first identified. It is also found in Europe and Asia, and reported cases in people have increased. Dogs are at higher risk than people because they are more exposed to ticks.

Many infected animals show no signs. When symptoms do occur in dogs, they commonly include fever, loss of appetite, swollen or painful joints, lameness that shifts from one leg to another, swollen lymph nodes, and lack of energy. If untreated, Lyme disease can damage the kidneys, nervous system, and heart. Lyme disease that affects the kidneys is one of the most serious forms in dogs and is often fatal. Nervous system disease can cause paralysis (inability to move) the face or seizures. The heart is rarely affected.

Lyme disease is usually diagnosed based on a dog’s symptoms and history of possible tick exposure. For example, a veterinarian might suspect Lyme disease in a dog with recent lameness, mild fever, and a known risk of tick contact.

Routine blood tests are not very useful for diagnosis because results are often normal even when infection is present. However, they can help rule out other diseases. Special tests to detect antibodies (proteins made by the immune system when fighting infection) become helpful about 4–6 weeks after infection starts and can support the diagnosis.

Treatment typically involves antibiotics for about 4 weeks. Most dogs with joint or leg symptoms improve quickly, although some don't fully recover. In some cases, the infection can persist and require additional treatment. Supportive care with fluids and other medications is important, especially when the kidneys, heart, or nervous system are affected. Some dogs develop long-term joint pain due to permanent damage.

Preventing Lyme disease relies heavily on tick control. Effective products such as sprays, medications taken by mouth, and treatments applied to the skin are available but must be used consistently for best protection. Vaccines are also available and might be recommended in areas where Lyme disease is common, especially before exposure occurs.

Any ticks found on a dog should be removed promptly to decrease the risk of disease transmission. Even though dogs don't directly infect people with Lyme disease, they can bring infected ticks into the home, where they can attach to people or other animals.