Borreliae are Gram-negative bacilli, which are larger than other spirochetes. They measure 0.2–0.5 mm in breadth and 3–30 mm in length. They are motile and stained readily with aniline dye, such as Giemsa and Wright stain. The genus Borrelia consists of many species, which are found as commensals on buccal and genital mucosa. Members of the genus Borrelia cause two important diseases in humans:
· Epidemic or louse-borne relapsing fever is caused by Borreliarecurrentis, whereas endemic relapsing fever is caused by asmany as 15 species of Borrelia. These include Borrelia duttoni, Borrelia henselae, Borrelia parkeri, Borrelia tunicatai, etc.
· Borrelia burgdorferi is responsible for causing Lyme disease.
B. recurrentis is the causative agent of relapsing fever, whichmanifests as one or more relapses of fever after the subsidence of primary paroxysm of fever.