The different manifestations of Lyme borreliosis do not show an even geographical distribution, which is probably due to the uneven distribution of the different B. burgdorferi genospecies. Only one of them, B. burgdorferi sensu stricto, has been implicated as the cause of disease in North America, but in Europe five genospecies, B. afzelii, B. garinii, B. burgdorferi sensu stricto, B. bavariensis and B. spielmanii are known to be pathogenic. Others such as B. valaisiana and B. lusitaniae and the rare B. bissetii are of unknown pathogenicity at present, though all have been detected rarely in human cases (Diza et al. 2004. Emerg Infect Dis. 10:1692-3, Lopes de Carvalho et al. 2008 Clin Rheumatol. 27:1587-91, Rudenko et al., 2008. J Clin Microbiol. 46:3540-3).
B. burgdorferi s.s. is strongly associated with both neurological and arthritic complications, B. afzelii seems to be associated with the degenerative skin condition, acrodermatitis chronica atrophicans, and B. garinii with neurological symptoms (Van Dam et al. 1993. J Clin Dis. 17:708-17), but these associations are not clear-cut and there is considerable overlap. B. garinii predominates in Western Europe and B. afzelii becomes more prevalent in northern, central and eastern regions, while there is some evidence that B. burgdorferi s.s. has been introduced from the west (Saint Girons et al. 1998. Zentralbl Bakteriol. 287:190-5; Rauter & Hartung. 2005. Appl Environ Microbiol. 71:7203-16)