Borrelia is a genus of bacteria of the spirochete class. It is a zoonotic, vector-borne disease transmitted primarily by ticks and some by lice, depending on the species. There are 37 known species of Borrelia.
Borreliosis (Lyme disease)
Of the 37 known species of Borrelia, 12 of these species are known to cause Lyme disease or borreliosis and are transmitted by ticks. The major Borrelia species causing Lyme disease are Borrelia burgdorferi, Borrelia afzelii, Borrelia garinii and Borrelia valaisiana.
Species and Strains
Until recently it was thought that only three genospecies caused Lyme disease (borreliosis): B. burgdorferi sensu stricto ( the predominant species in North America, but also present in Europe); B. afzelii; and B. garinii (both predominant in Eurasia). To date the complete genome of B. burgdorferi sensu stricto strain B31, B. afzelii strain PKo and B. garinii strain PBi is known. B. burgdorferi strain B31 was derived by limited dilutional cloning from the original Lyme-disease tick isolate derived by Alan Barbour. There are over 300 species or strains of Borrelia world wide with apx 100 in the U.S. and it is unknown how many cause lyme like sickness, but many of them may.
At present, diagnostic tests are based only on B. burgdorferi sensu stricto (the only species used in the U.S.), B. afzelii, and B. garinii.
- B. valaisiana was identified as a genomic species from Strain VS116, and named B. valaisiana in 1997. It was later detected by Polymerase chain reaction (PCR) in human cerebral spinal fluid (CSF) in Greece. B. valaisiana has been isolated throughout Europe, as well east Asia.
Newly discovered genospecies have also been found to cause disease in humans:
- B. lusitaniae  in Europe (especially Portugal), North Africa and Asia.
Additional B. burgdorferi sensu lato genospecies suspected of causing illness, but not confirmed by culture, include B. japonica, B. tanukii and B. turdae (Japan); B. sinica (China); and B. andersonii (U.S.). Some of these species are carried by ticks not currently recognized as carriers of Lyme disease.
The B. miyamotoi spirochete, related to the relapsing fever group of spirochetes, is also suspected of causing illness in Japan. Spirochetes similar to B. miyamotoi have recently been found in both I. ricinus ticks in Sweden and I. scapularis ticks in the U.S.
Apart from this group of closely related genospecies, additional Borrelia species of interest include B. lonestari, a spirochete recently detected in the Amblyomma americanum tick (Lone Star tick) in the U.S. B. lonestari is suspected of causing STARI (Southern Tick-Associated Rash Illness), also known as Masters disease in honor of its discoverer Ed Masters. The illness follows a Lone Star tick bite and clinically resembles Lyme disease, but sufferers usually test negative for Lyme.There is currently no diagnostic test available for STARI/Masters, and no official treatment protocol, though antibiotics are generally prescribed.
Other Borrelia species cause relapsing fever such as Borrelia recurrentis, caused by the human body louse. No animal reservoir of B. recurrentis exists. Lice that feed on infected humans acquire the Borrelia organisms that then multiply in the gut of the louse. When an infected louse feeds on an uninfected human, the organism gains access when the victim crushes the louse or scratches the area where the louse is feeding. B. recurrentis infects the person via mucous membranes and then invades the bloodstream.
Other tick-borne relapsing infections are acquired from other species, such as Borrelia hermsii or Borrelia Parkeri, which can be spread from rodents, and serve as a reservoir for the infection, via a tick vector. Borelia hermsii and Borrelia recurrentis cause very similar diseases although the disease associated with Borrelia hermsii has more relapses and is responsible for more fatalities, while the disease caused by B. recurrentis has longer febrile and afebrile intervals and a longer incubation period.
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