Lyme Disease (Lyme Borreliosis) in Dogs
Lyme disease, which is caused by Borrelia burgdorferi bacteria and transmitted through the bite of a tick, affects domestic animals (dogs, horses, and possibly cats) and humans. At least 3 known species of ticks can transmit Lyme disease. However, the great majority of Lyme disease transmissions are due to the bite of a very tiny tick commonly called the deer tick, or black-legged tick. The scientific name of the tick involved on the west coast is Ixodes pacificus and Ixodes scapularis elsewhere in the United States. Ixodes ricinus and Ixodes persulcatus are the primary vectors in Europe and Asia. It is important to note that ticks do not cause Lyme disease; they merely harbor and transmit the bacteria that cause it.
Although the tick prefers certain creatures—such as voles, white-footed mice, or deer—upon which to feed during the various stages of its life cycle, it is quite willing to feed on humans or dogs. Regardless of its stage of development (larva, nymph, or adult Ixodes tick), if the tick carries the bacteria in its body, people and dogs can become infected if bitten. Once a tick attaches, it takes 1-2 days for it to transmit the bateria that cause Lyme disease, so prompt removal of ticks is important. Risk of transmission is highest during periods when the nymphs (spring) and adults (spring and fall) are actively seeking hosts.
Lyme disease in dogs has been reported in every state in the United States, but certain geographical areas are much more likely to harbor bacteria-carrying ticks than others. Infection rates of ticks vary, but can be as high as 50%. Areas in the United States where it occurs most often include the Atlantic seaboard, upper Midwest, and Pacific coast. The disease is actually named after the town Lyme, Connecticut where an early outbreak was first described. Lyme disease is also seen in Europe, Asia, Australia, and elsewhere. The importance of Lyme disease as a zoonotic disease is increasing. Although the rate of occurrence of the disease in a geographic area is similar in both animals and humans, animals, especially dogs, are at significantly higher risk because of their greater exposure to ticks.
The signs of Lyme disease vary. Many animals can have Lyme disease and show no signs. In dogs, the most common signs include fever, loss of appetite, painful or swollen joints, lameness that progresses from mild to severe, swollen lymph nodes, and lethargy. If Lyme disease is left untreated it can lead to damage in the kidneys, nervous system, and heart. Lyme disease affecting the kidneys is the second most common syndrome in dogs and is generally fatal. Facial paralysis and seizure disorders have been reported in the disease form affecting the nervous system. The form of the disease that affects the heart is rare.
The diagnosis of Lyme disease is often based on the signs and history. For example, a veterinarian might suspect Lyme disease in a dog with recent lameness, a mild fever, and a history that includes possible exposure to ticks. Standard blood studies are not very helpful in diagnosis because the results tend to fall within normal ranges despite signs of infection. Antibodies against the disease-causing bacteria can often be detected 4 to 6 weeks after the initial infection and help confirm the diagnosis.
Antibiotics (usually for 2 to 4 weeks) are required in all cases of Lyme disease. Rapid response is seen in limb and joint disease in most cases, although incomplete resolution of signs is seen in a significant number of affected animals. Infection in animals may persist in spite of antibiotics and may require a second round of treatment. Additional therapy to help the affected organ systems and signs is also important, especially when the disease affects the kidneys, heart, or nerves. Some affected dogs will experience chronic, lifelong joint pain from the damage caused by the bacteria.
Tick avoidance plays a role in disease control. While highly effective products (such as sprays and monthly oral or “spot-on” products) are available for use with dogs, they must be used consistently in order to provide effective longterm tick control. Vaccines that prevent infection in dogs are available; these appear to work best when given to dogs before they are exposed to Lyme-causing bacteria. Vaccination and annual boosters may be recommended by your veterinarian if you live in an area where Lyme disease is common. Any ticks found on your dog should be promptly removed in order to help prevent transmission of Lyme disease and other diseases spread by ticks. Dogs are not the direct source of infection in people. Pets may bring unattached infected ticks into the household and if they then attach to another animal or person, they may transmit Lyme disease.