Lyme borreliosis.

Lyme borreliosis is the most common tick-borne disease in the northern hemisphere. It is a zoonosis caused by several species of Borrelia burgdorferi sensu lato and transmitted by the bite of infected ticks of the Ixodes ricinus complex. Lyme borreliosis in North America and Europe differs in certain respects, likely reflecting the different Borrelia species that cause human disease in these locations. The earliest manifestation of Lyme borreliosis is the skin lesion erythema migrans, which develops at the tick bite site, typically 7-14 days after the bite. Some untreated patients will then (within the first few weeks or months after onset of the infection) develop additional erythema migrans skin lesions or other clinical manifestations such as borrelial lymphocytoma, nervous system involvement or carditis. Several months or even years after infection onset, Lyme arthritis or acrodermatitis chronica atrophicans may develop. The diagnosis of typical erythema migrans is clinical, whereas for all other manifestations the diagnosis is supported via serological testing. Treatment with an appropriate antibiotic will result in resolution of clinical symptoms in most patients; however, some patients experience prolonged subjective symptoms, which usually improve over time. Repeated courses of antimicrobials are not beneficial except in rare cases when there is objective evidence of treatment failure.