The borrelia belong to the family of the spirochetes. They are gram negative thin, about 20 µm long, very motile bacteria.
In human medicine especially the borrelia ofthe burgdorferi-complex (B. burgdorferi, B. garinii, B. afzelii and B. spielmannii) are of importance, as they cause Lyme disease and also B. duttonii und B. recurrentis who cause relapsing fever. B. recurrentis is transmitted by lice (Pediculus humanus), B. duttonii by ticks (argasidae).
The vector of Lyme borreliosis in Europe is also a tick (Ixodes ricinus). Transmission occurs via tick-bite. The transmission probability rises significantly 24 hours after attachement which makes a fast removal of the parasite important. About 10 - 35 % of ticks are infected with borrelia.
This digitally colored scanning electron microscope image (SEM) shows a group of many gram negative, anearobic Borrelia burgdorferi bacteria, who were grown in a pure culture.
Source: CDC/ Claudia Molins