Borrelia burgdorferi s.l., the infectious agent of Lyme borreliosis.

described at the beginning of the 20th century in Sweden [1] and Germany [2], and an association to a tick-borne nonpyogenic bacterium responsive to penicillin was postulated [3]. In the mid-1970s, in Lyme, Conn., USA, the rheumatologist Allen Steere observed a geographic clustering of children with juvenile rheumatoid arthritis, which was often preceded by a distinctive skin rash, erythema migrans (EM), and linked to antecedent tick bites. The multisystemic nature of the illness was recognized, with adoption of the term Lyme disease (or Lyme borreliosis) [4]. In 1983, W. Burgdorfer detected spirochetes in the midgut of the tick Ixodes ricinus and identified this ectoparasite in this way as a vector of the newly described LB [5]. A few years later, Barbour succeeded in culturing the spirochetes in a modified Kelly’s medium (BSK).