Lyme disease is caused by the spirochete bacteria Borrelia burgdorferi. The spirochete is acquired through the bite of an infected tick. Lyme disease is now regarded as the most common tick-borne illness in the United States.
This disease was first recognized in 1975, following an outbreak of what appeared to be acute arthritis in several rural communities in southeastern Connecticut, including the town of Old Lyme. Currently, most cases are found in wooded locations in the Northeast, upper Midwest (including much of Wisconsin and Minnesota), northern California, and the Pacific Northwest.
The white-footed mouse is the principal reservoir for the spirochete. Birds can also harbor it. The white-tailed deer supports the tick, but not the spirochete. Lyme disease is spread primarily during tick season (May through August), peaking in the month of July, but ticks can be active any time the temperature is over 32°F (0°C).
The disease in dogs is most commonly characterized by the sudden onset of lameness. In fact, lameness is often the only sign of infection. One or more joints may become swollen and painful to the touch. Some dogs run a fever and experience weakness, lethargy, loss of appetite, and weight loss. The lameness may last only a few days, but in some cases it becomes chronic and persists or recurs for months.
Kidney problems are the next most common sign. An acute cardiac syndrome is quite rare. Both of these syndromes are usually fatal.
Most dogs exposed to Lyme disease do not become ill. Serological blood tests will indicate whether a dog has been exposed to the disease. Dogs may not test positive until a few weeks after exposure. New serologic tests can distinguish between dogs with vaccine immunity and dogs with natural exposure. A rising antibody titer in the absence of recent vaccination, however, indicates active infection. Western Blot and ELISA blood tests are now both used to detect exposure. Many dogs who test positive for Lyme disease will also have other tick-borne diseases, such as ehrlichiosis and babesiosis.
X-rays of swollen joints show fluid without degenerative joint changes. Synovial fluid analysis (in which a needle is inserted into a joint to remove fluid for examination) may show spirochetes.
Treatment: Antibiotics are given for a minimum of two to four weeks. Amoxicillin and doxycycline are among the most effective.
Prevention: Ticks must attach for 5 to 20 hours before they are capable of transmitting infection. Accordingly, a daily inspection with removal of ticks will prevent many dogs from becoming infected.
Tick collars such as Preventic, and tick control on the premises, help reduce the occurrence of Lyme disease. Frontline is a flea-control preparation that kills ticks for up to 30 days following a single application. Advantix is another topical product that kills ticks. For more information, see Ticks.
There is a vaccine to prevent Lyme disease in dogs. It may be advisable for dogs at risk for Lyme disease. Discuss this with your veterinarian.
Public health considerations: Lyme disease is a serious illness in humans. Dogs do not transmit Lyme disease to humans, although they can spread the ticks carrying the spirochete. Ticks may transfer to people before feeding on the dog, although this is not common. Once a tick starts feeding on a dog, it will not seek a second host. Dispose very carefully of any ticks you remove from your dog. The best method is to put them in a jar with a bit of alcohol, seal the jar, and throw it away.