The spirochaete Borrelia burgdorferi (sensu lato) is the cause of Lyme
borreliosis, a common tick-borne disease with a wide geographical dis
tribution. B. burgdorferi s.l. was first isolated in 1982 after a clin
ical and epidemiological study of an unusual outbreak of arthritis in
children in the town of Old Lyme, Connecticut, USA. Despite this recen
t discovery, there is evidence that Lyme borreliosis has existed for m
any years. Clinical manifestations are diverse, but antibiotic therapy
is largely successful when initiated early in the disease. Molecular-
based studies have improved the laboratory diagnosis of Lyme borrelios
is and played a significant role in ecological and taxonomic investiga
tions of the pathogen. B. burgdorferi s.l. is now divided into some ni
ne genospecies and genomic groups, some of which have been associated
with particular manifestations of disease, while the number of tick sp
ecies found to be competent vectors has also increased. The emerging e
cology of B. burgdorferi s.l. is more complex than originally describe
d and, consequently, the assessment of risk of disease to an individua
l bitten by a tick should include establishing the identity of the tic
k, duration of attachment and degree of engorgement, as well as consid
eration of the individual's way of life and environment. (C) 1998 Chap
man & Hall.