Lyme disease or Borreliosis is the most common tick borne disease in Europe and North America. The disease is caused by the spirochete Borrelia burgdorferi sensu lato which is transmitted by the bite of ticks from the genus Ixodes. The organism can be divided into 36 species differing in their geographic distribution as well as in their pathogenity for humans. Whilst in North America the vast majority of infections are caused by B. burgdorferi sensu stricto, in Europe B. afzelii and garinii are the most dominant strains.CLINICAL INFORMATION: On the basis of symptoms, Borreliosis divided into three stages:1. Local infection: Typically this manifests as Erythema migrans which appears within 5-28 days after infection.2. This is characterised through dissemination of the pathogen leading to meningopolyneuritis Garin-Boujadoux-Bannwarth-syndrome (4-16 weeks after infection).3. This is a chronic infection with (a) skin manifestations (Acrodermatitis chronica atrophicans, mainly B. afzelii), (b) neuroborreliosis (mainly B. garinii) and (c) chronic mono- or oligoarticular arthritis (Lyme disease, all Borrelia strains). TESTING ALGORITHMA two tier diagnostic algorithm is recommended for the laboratory detection of specific antibodies against Borrelia. To obtain a high diagnostic efficiency screening is performed using a very sensitive enzyme immunoassay (EIA). Specimens negative by EIA need not to be tested further, all samples with a positive or equivocal result must be confirmed using a highly specific standardized Western Blot. If a patient with suspected early Borreliosis has a negative serology, serologic evidence of infection is best obtained by testing of paired acute- and convalescent phase serum samples.