Microbiology of Lyme disease

Lyme disease, or borreliosis, is caused by spirochetal bacteria from the genus Borrelia, which has 52 known species. Three species (Borrelia garinii, Borrelia afzelii, and Borrelia burgdorferi s.s.) are the main causative agents of the disease in humans, while a number of others have been implicated as possibly pathogenic. Borrelia species in the species complex known to cause Lyme disease are collectively called Borrelia burgdorferi sensu lato (s.l.). The single species Borrelia burgdorferi sensu stricto (s.s.), a member of the complex, is responsible for nearly all cases of Lyme disease in North America.

Borrelia are microaerophilic and slow-growing. The primary reason for late diagnosis of Lyme disease is due to strain diversity. The species differ in clinical symptoms and presentation as well as geographic distribution.

Except for Borrelia recurrentis (which causes louse-borne relapsing fever and is transmitted by the human body louse), all known species are believed to be transmitted by ticks.