Lyme disease microbiology

Lyme disease, or borreliosis, is caused by spirochetal bacteria from the genus Borrelia, which has 52 known species. Three main 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.) not to be confused with the single species in that complex Borrelia burgdorferi sensu stricto which is responsible for all cases of Lyme disease in North America. Lyme disease, or borreliosis, is caused by spirochetal bacteria from the genus Borrelia, which has 52 known species. Three main 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.) not to be confused with the single species in that complex Borrelia burgdorferi sensu stricto which is responsible for all cases of Lyme disease in North America. Borrelia are microaerophilic and slow-growing—the primary reason for the long delays when diagnosing Lyme disease—and have been found to have greater strain diversity than previously estimated. The strains differ in clinical symptoms and/or 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. Until recently, only three genospecies were thought to cause Lyme disease (borreliosis): B. burgdorferi s.s. (the predominant species in North America, but also present in Europe); B. afzelii; and B. garinii (both predominant in Eurasia). Thirteen distinct genomic classifications of Lyme disease bacteria have been identified worldwide. These include but are not limited to B. burgdorferi s.s., B. afzelii, B. garinii, B. valaisana, B. lusitaniae, B. andersoni, 25015, DN127, CA55, 25015, HK501, B. miyamotoi, and B. japonica. Many of these genomic groups are country or continent specific. For example, without migration, B. japonica is only prevalent in the eastern hemisphere. The genomic variations have direct implications on the clinical symptoms of tick-borne Lyme disease. For example, B. burgdorferi s.s.’s tick-borne Lyme disease may manifest with arthritis-like symptoms. In contrast, B. garinii’s tick-borne Lyme disease may cause an infection of the central nervous system. Newly discovered genospecies have also been found to cause disease in humans: Additional B. burgdorferi sensu lato genospecies suspected of causing illness, but not confirmed by culture, include B. japonica, B. tanukii and B. turdae (Japan); B. sinica (China); and B. andersonii (U.S.). Some of these species are carried by ticks not currently recognized as carriers of Lyme disease. The B. miyamotoi spirochete, related to the relapsing fever group of spirochetes, is also suspected of causing illness in Japan. Spirochetes similar to B. miyamotoi have recently been found in both Ixodes ricinus ticks in Sweden and I. scapularis ticks in the U.S.