The distribution of Borrelia burgdorferi sensu lato, the
Lyme borreliosis agent, was surveyed in British ticks in the collection of the Natural History Museum, London. Alcohol-preserved specimens of eight species of ticks known to attack humans were studied: Ixodes ricinus, I. hexagonus, I. uriae, I. trianguliceps, Dermacentor reticulatus, Haemaphysalis punctata, Rhipicephalus sanguineus and Argas vespertilionis. The sample comprised all life stages and originated from a wide range of host species, collection dates (1896-1994) and geographical localities in England, Scotland and Wales. Borrelia burgdorferi s.l. DNA, detected by a polymerase chain reaction that targeted the outer surface protein A gene, was found in all eight species. The overall proportion of PCR-positive specimens ranged from 7.8% for I. hexagonus (mostly from mustelids and hedgehogs) to 98.3% for I. uriae (mostly from seabirds). Borrelia burgdorferi s.l. DNA was found for the first time in the bat parasite A. vespertilionis (85.3%). The spirochaete is newly recorded in British populations of I. trianguliceps (97.4%, mostly from voles, mice and shrews), D. reticulatus (12.5% from dog and man) and R. sanguineus (30% from dogs and human dwellings). Of the four tick species with larvae available for testing, examples of I. ricinus, I. uriae and A. vespertilionis were PCR positive, as were significantly more nymphs than adults of I. ricinus, I. hexagonus and A. vespertilionis. Analyses showed that B. burgdorferi s.l. has been consistently present in British tick populations since at least 1897. Ticks positive for B. burgdorferi s.l. DNA were collected in all months of the year, throughout Britain, and were found on a wide range of mammal and bird species. PCR positivity does not prove vector or reservoir competence, but the use of archived material has demonstrated an extensive range of host-tick relationships involving B. burgdorferi s.l. in Britain for > 100 years.