Borrelia

Borrelia
Borrelia burgdorferi the causative agent of Lyme disease (borreliosis) magnified 400 times
Scientific classification
Domain:	Bacteria
Phylum:	Spirochaetes
Order:	Spirochaetales
Family:	Spirochaetaceae
Genus:	Borrelia Swellengrebel 1907
Species
Borrelia afzelii Canica et al. 1994 Borrelia americana Rudenko et al. 2010 Borrelia andersonii ♠ Marconi et al. 1995 Borrelia anserina ♦ (Sakharoff 1891) Bergey et al. 1925 Borrelia baltazardii ♦ (ex Karimi et al. 1979) Karimi et al. 1983 Borrelia bavariensis ♠ Margos et al. 2009 Borrelia bissettii ♠ Postic et al. 1998 Borrelia brasiliensis ♦ Davis 1952 Borrelia burgdorferi Johnson et al. 1984 emend. Baranton et al. 1992 (Lyme disease spirochete) Borrelia californiensis ♠ Postic et al. 2007 Borrelia carolinensis Rudenko et al. 2011 Borrelia caucasica ♦ (Kandelaki 1945) Davis 1957 Ivanova et al. 2014 Borrelia coriaceae Johnson et al. 1987 Borrelia crocidurae ♦ (Leger 1917) Davis 1957 ♦ (Mazzotti 1949) Davis 1957 Borrelia duttonii ♦ (Novy and Knapp 1906) Bergey et al. 1925 Casjens et al. 2011 Borrelia garinii Baranton et al. 1992 ♦ (Heisch 1953) Davis 1957 ♦ (Garnham 1947) Davis 1948 Borrelia hermsii ♦ (Davis 1942) Steinhaus 1946 ♦ (de Buen 1926) Steinhaus 1946 Borrelia japonica Kawabata et al. 1994 Schwan et al. 2009 Fingerle et al. 2016 Borrelia kurtenbachii Margos et al. 2010 ♦ (Sofiev 1941) Davis 1948 Borrelia lonestari ♠ Barbour et al. 1996 Borrelia lusitaniae Le Fleche et al. 1997 Borrelia mayonii Pritt et al. 2016 ♦ Davis 1956 ♠ Hougen 1974 Borrelia microti ♠ Borrelia miyamotoi Fukunaga et al. 1995 Mitani et al. 2014 Borrelia parkeri ♦ (Davis 1942) Steinhaus 1946 ♦ (Dschunkowsky 1913) Steinhaus 1946 PopeJG et al. 1962 Borrelia recurrentis ♦ (Lebert 1874) Bergey et al. 1925 Borrelia sinica Masuzawa et al. 2001 Borrelia spielmanii Richter et al. 2006 Loh et al. 2016 Borrelia tanukii Fukunaga et al. 1997 " Lin et al. 2005 Borrelia theileri ♦ (Laveran 1903) Bergey et al. 1925 Borrelia tillae ♦ Zumpt and Organ 1961 Borrelia turcica Güner et al. 2004 Borrelia turdi Fukunaga et al. 1997 Borrelia turicatae ♦ (Brumpt 1933) Steinhaus 1946 Borrelia valaisiana Wang et al. 1997 Borrelia venezuelensis ♦ (Brumpt 1921) Brumpt 1922 Borrelia vincentii ♥ "" Margos et al. 2015

Borrelia is a genus of bacteria of the spirochete phylum.^[1] It causes Lyme disease, also called Lyme borreliosis, a zoonotic, vector-borne disease transmitted primarily by ticks and by lice, depending on the species of bacteria.^[2] The genus is named after French biologist Amédée Borrel (1867–1936), who first documented the distinction between a species of Borrelia, B. anserina, and the other known type of spirochete at the time, Treponema pallidum.^[3] This bacterium must be viewed using dark-field microscopy,^[4] which make the cells appear white against a dark background. Borrelia species are grown in Barbour-Stoenner-Kelly medium.^[4] Of 52 known species of Borrelia, 20 are members of the Lyme disease group (with an additional 3 proposed),^[5] 29 belong to the relapsing fever group, and two are members of a genetically distinct third group typically found in reptiles.^[3] The Lyme disease group has been proposed to be split based on genetic diversity and moved to their own genus, Borelliella,^[6] but this change is not widely accepted.^[3] This bacterium uses hard and soft ticks and lice as vectors.^[7][8] Testing for the presence of the bacteria in a human includes two-tiered serological testing, including immunoassays and immunoblotting.^[9]

Biology[]

Borrelia species are members of the family Spirochaetaceae, so present the characteristic spirochete (spiral) shape. Most species are obligate anaerobes, although some are aerotolerant.^[10] Borrelia species have an outer membrane that contains a substance similar to lipopolysaccharides, an inner membrane, and a layer of peptidoglycan in a periplasmic space, which classifies them as Gram-negative.^[4] However, this result is not easily visualized using Gram staining.^[4] They are typically 20–30 μm long and 0.2–0.3 μm wide.^[4]

Spirochetes move using axial filaments called endoflagella in their periplasmic space.^[4] The filaments rotate in this space, between the outer membrane and the peptidoglycan layer, propelling the bacterium forward in a corkscrew-like motion.^[4] The outer membrane of Borrelia species contains outer surface proteins (Osp) that play a role in their virulence.^[4]

Phylogeny[]

The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN)^[1] and National Center for Biotechnology Information (NCBI)^[1] and the phylogeny is based on 16S rRNA-based LTP release 111 by the All-Species Living Tree Project.^[1]

?B. lonestari ♠ Barbour et al. 1996     ?B. microti ♠       B. turcica Güner et al. 2004       B. coriaceae Johnson et al. 1987     B. miyamotoi Fukunaga et al. 1995       S. burgdorferi species‑group   ?Candidatus B. texasensis Lin et al. 2005     ?B. andersonii ♠ Marconi et al. 1995     ?B. bavariensis ♠ Margos et al. 2009     ?B. bissettii ♠ Postic et al. 1998     ?B. californiensis ♠ Postic et al. 2007     ?B. kurtenbachii ♠ Margos et al. 2010     ?B. spielmanii Richter et al. 2006       B. tanukii Fukunaga et al. 1997       B. afzelii Canica et al. 1994       B. turdi Fukunaga et al. 1997     B. valaisiana Wang et al. 1997             B. americana Rudenko et al. 2010       B. carolinensis Rudenko et al. 2011     B. burgdorferi (Lyme disease spirochete)       B. garinii Baranton et al. 1992     B. lusitaniae Le Fleche et al. 1997         B. japonica Kawabata et al. 1994     B. sinica Masuzawa et al. 2001

Notes:
♦ Type strain lost or not available
♠ Strains found at the NCBI, but not listed in the LSPN
♥ Strains neither lodged at NCBI nor listed in the LPSN

Vectors[]

Ticks[]

Hard ticks of the family Ixodidae are common vectors of Borellia bacteria^[11] and are the only type of ticks shown to transmit Lyme disease bacteria to humans.^[12]

Global hard tick species that cause Lyme disease^[7]

Region	Tick species	Common name
East and Midwest (US)	Ixodes scapularis	Black-legged tick, deer tick
Pacific Coast (US)	Ixodes pacificus	Western black-legged tick
Europe	Ixodes ricinus	Sheep tick
Asia	Ixodes persulcatus	Taiga tick

Other species are carried by soft ticks. The soft tick Ornithodoros carries the species of Borellia that cause relapsing fever.^[8] Another species, B. anserina, is carried by the soft tick Argas.^[3] Inside the ticks, the bacteria grow in the midgut and then travel to the salivary glands to be transmitted to a new host.^[12] Ticks can spread the bacteria to each other when co-feeding.^[11] If an animal has been infected by a tick and then is bitten by a second tick, the second tick can become infected.^[13] The bacteria are most commonly transmitted to humans through ticks in the nymph stage of development, because they are smaller and less likely to be noticed and removed.^[13] The ticks must have around 36 to 48 hours of contact with a host to successfully transmit the bacteria.^[13]

Lice[]

Lice that feed on infected humans acquire the Borrelia organisms that then multiply in the hemolymph and gut of the lice.^[8] 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.^[8] The U. S. Centers for Disease Control and Prevention reported that no credible evidence shows that lice can carry Borrelia.^[13]

Lyme disease[]

Of the 52 known species of Borrelia, 20 belong to the Lyme disease group and are transmitted by ticks.^[3] Eight are known to cause Lyme disease or Borreliosis.^[14] The major Borrelia species causing Lyme disease are Borrelia burgdorferi, Borrelia afzelii, and Borrelia garinii.^[15] All species that cause Lyme disease are referred to collectively as B. burgdorferi sensu lato,^[9] while B. burgdorferi itself is specified as B. burgdorferi sensu stricto.^[9][12] B. burgdorferi was previously believed to be the only species to cause Lyme disease in the US, but B. bissettiae and a new species called B. mayonii cause Lyme disease in the US, as well.^[15] The remaining five human pathogenic species occur only in Europe and Asia.

Relapsing fever[]

Relapsing fever (RF) borreliosis often occurs with severe bacteremia.^[16] Twenty-five species of Borrelia are known to cause relapsing fever.^[17] While most species use the soft tick family Argasidae as their vector, some outliers live in hard ticks or lice.^[17] Relapsing fever can be spread epidemically through lice or endemically through ticks.^[8]

B. recurrentis, a common species underlying relapsing fever, is transmitted by the human body louse; no other animal reservoir of B. recurrentis is known.^[8] B. recurrentis infects the person via mucous membranes and then invades the bloodstream.^[8]

Other tick-borne relapsing infections are acquired from other species, such as B. hermsii, B. parkeri, or B. miyamotoi,^[18] which can be spread from rodents, and serve as a reservoir for the infection, via a tick vector. B. hermsii and B. recurrentis cause very similar diseases, although the disease associated with B. 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.

Diagnosis[]

Direct tests include culture of Borrelia from skin, blood, or cerebrospinal fluid (CSF), and detection of genetic material by polymerase chain reaction in skin, blood, or synovial fluid. Two-tiered serological testing is performed for differential diagnosis of Borrelia infection. The first-tier tests detect specific antibodies (IgM and IgG together or separately) and include enzyme-linked immunoassays (e.g. ELISAs) and immunofluorescent assays. Positive results for first-tier tests are confirmed using second-tier testing. The second tier consists of standardized immunoblotting, either by using Western blots or blots striped with diagnostically important purified antigens. Positive results for second-tier tests are confirmatory for the presence of Borrelia infection.^[9][19] Spirochetes can also be seen using Wright-stained blood smears.^[8]

References[]

Further reading[]

External links[]

• Borrelia genomes and related information at PATRIC, a Bioinformatics Resource Center funded by NIAID
• Borrelia Microbe Wiki Page
• NCBI Borrelia Taxonomy Browser