Characteristics of Lyme disease spirochetes in archived European ticks.

To determine whether the characteristics of the Lyme disease spirochete (Borrelia burgdorferi) in Europe may have changed during the past century, DNA was amplified from archived Ixodes ricinus ticks. Tick DNA could be amplified, even when ticks had been stored under museum conditions for nearly a century. Spirochetal DNA was detected by polymerase chain reaction in 6 ticks preserved for as long as a century; the oldest was collected in 1884. Borrelia garinii, which predominates in modern ticks in the region, infected 3 of these older ticks, and the presently infrequent B. burgdorferi sensu stricto infected 2. These data indicate that residents of Europe have been exposed to diverse Lyme disease spirochetes at least since 1884, concurrent with the oldest record of apparent human infection.