ABSTRACT
Members of the genus Borrelia are Gram-negative motile spiral rods driven by endoflagella. Lyme disease is the most common tick-borne disease in North America and Europe. There are three genospecies within the Borrelia burgdorferi complex B. burgdorferi (sensu lato), B. burgdorferi (sensu stricto), B. garinii, and B. afzelii. Strains found in North America belong to B. burgdorferi sensu stricto, whereas the other two species are found in Europe and Asia.
The bacteria are maintained in an enzootic cycle involving hard-bodied ticks belonging to the Ixodes ricinus species complex and a wide range of reservoir vertebrate hosts. Spirochetes enter the tissues while the tick takes a blood meal. The bacteria may establish a localized infection in the skin at the site of the tick bite, producing a characteristic skin lesion known as erythema migrans (EM). In addition, they may disseminate via the blood stream and/or lymphatics. The organism demonstrates a tropism for the central nervous system (CNS), heart, joints, and eyes, all of which may become chronically infected, giving rise to neurologic disease, carditis, arthritis, and conjunctivitis. Borreliae can also persist in skin and perhaps the CNS for years without causing symptoms. Many of the outer surface lipoproteins (OSPs) of the bacteria are phase and/or antigenically variable. The spirochetes have a number of methods of avoiding the innate and acquired immune response which may contribute to their latency. In patients with signs and symptoms consistent with Lyme disease, a diagnosis is confirmed by antibody detection tests. The Lyme spirochetes are susceptible to several antibiotics such as doxycycline.
