Lyme disease in people is now the most common vector-borne disease in the United States, with over 153,000 cases reported to the Centers for Disease Control (CDC) by 49 states and the District of Columbia between 1993 and 2002. Lyme disease has been documented in every state in the United States except Montana, but there are distinct areas that are considered more endemic than others. These include the Northeast and mid-Atlantic coast (MA, RI, NY, NJ, PA, MD, DE, CT), the upper Midwest (MN, WI), and the Northwest (CA).
Since the early 1990s, Lyme disease in dogs has been the focus of much research relating to the origin, treatment, and prevention of infection. The causative agent is a corkscrew-shaped spirochete named Borrelia burgdorferi. This bacterial organism is transmitted primarily by nymphal ticks of Ixodes scapularis (black-legged or deer tick) between May and July in the Northern Hemisphere.
It is reported, however, that only approximately 5-10% of infected dogs develop overt clinical signs after infection with the causative agent, B. burgodorferi. However, it is clear that dogs can become infected with B. burgdorferi after being infested with I. scapularis ticks. They develop joint disease and mild to moderate arthritis in more than one joint, whether they become symptomatic or not.
Furthermore, treatments for Lyme disease in dogs can have mixed success. Antimicrobial therapy with tetracycline, doxcycline, chloramphenicol, or antibiotics like cephalosporins for 10 to 30 days is believed to be effective in treating Lyme disease in dogs, and lack of response after three days of antibiotic usage is considered to be cause for reevaluation of the diagnosis. However, it has been proven that dogs can become persistently (chronically) infected after natural tick challenge exposure with B. burgdorferi, despite prolonged courses of antibiotic therapy.
Because Borrelia organisms can persist for many months despite treatment, preventing Lyme disease through vaccination and reduction in tick numbers is the most logical approach.