Borrelia

Borrelia species are members of the family Spirochaetaceae, so present the characteristic spirochete (spiral) shape. Most species are obligate anaerobes, although some are aerotolerant. 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. However, this result is not easily visualized using Gram staining. They are typically 20–30 μm long and 0.2–0.3 μm wide. Spirochetes move using axial filaments called endoflagella in their periplasmic space. The filaments rotate in this space, between the outer membrane and the peptidoglycan layer, propelling the bacterium forward in a corkscrew-like motion. The outer membrane of Borrelia species contains outer surface proteins (Osp) that play a role in their virulence. ==Phylogeny==

The taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) and National Center for Biotechnology Information (NCBI): Species incertae sedis: • "Ca. Borrelia africana" Ehounoud et al. 2016 • "Ca. Borrelia algerica" Fotso et al. 2015 • "Ca. Borrelia aligera" Norte et al. 2020 • "Ca. Borrelia amblyommatis" corrig. Jiang et al. 2021 ["Ca. Borrelia javanense" Jiang et al. 2021] • Borrelia baltazardii corrig. Karimi et al. 1979 ex Karimi et al. 1983 • Borrelia brasiliensis Davis 1952 • "Ca. Borrelia caatinga" de Oliveira et al. 2023 • Borrelia caucasica (Kandelaki 1945) Davis 1957 • "Ca. Borrelia darwini" Parrague-Migone et al. 2025 • Borrelia dugesii (Mazzotti 1949) Davis 1957 • "Ca. Borrelia fainii" Qiu et al. 2019 • Borrelia graingeri (Heisch 1953) Davis 1957 • Borrelia harveyi (Garnham 1947) Davis 1948 • "Ca. Borrelia ibitipocensis" corrig. Muñoz-Leal et al. 2020 • "Ca. Borrelia ivorensis" Ehounoud et al. 2016 • "Ca. Borrelia johnsonii" Schwan et al. 2009 • "Ca. Borrelia kalaharica" Fingerle et al. 2016 • Borrelia latyschewii (Sofiev 1941) Davis 1948 • "Ca. Borrelia limariensis" Parrague-Migone et al. 2025 • "Borrelia lonestari" Barbour et al. 1996 • "Ca. Borrelia mahuryensis" Binetruy et al. 2020 • Borrelia mazzottii Davis 1956 • "Borrelia merionesi" Hougen 1974 non (Blanc & Maurice 1948) Davis 1948 • "Borrelia microti" (Rafyi 1946) Davis 1948 • "Ca. Borrelia mimona" Weck et al. 2024 • "Ca. Borrelia mvumii" Mitani et al. 2004 • "Borrelia myelophthora" (Steiner 1931) Ahrens & Muschner 1958 • "Borrelia nietonii" Schwan et al. 2024 • "Ca. Borrelia octodonta" Santodomingo et al. 2024 • "Ca. Borrelia paulista" Weck et al. 2022 • "B. rubricentralis" Gofton et al. 2023 • "Ca. B. sibirica" Sabitova et al. 2022 • "Ca. Borrelia texasensis" Adeolu & Gupta 2014 • Borrelia theileri (Laveran 1903) Bergey et al. 1925 • Borrelia tillae Zumpt & Organ 1961 • "B. undatumii" Gofton et al. 2023 • Borreliella bissettii (Margos et al. 2016) Gupta 2020 • Borreliella kurtenbachii (Margos et al. 2013) Adeolu & Gupta 2015 == Vectors ==

Ticks Hard ticks of the family Ixodidae are common vectors of Borellia bacteria and are the only type of ticks shown to transmit Lyme disease bacteria to humans. Some tick species of the Ambylomma genus are vectors of Candidatus Borrelia mahuryensis in South America. 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. The ticks must have around 36 to 48 hours of contact with a host to successfully transmit the bacteria. Lice Lice that feed on infected humans acquire the Borrelia organisms that then multiply in the hemolymph and gut of the lice. 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. The U. S. Centers for Disease Control and Prevention reported that no credible evidence shows that lice can carry Borrelia. == Pathology ==

Lyme disease Of the 52 known species of Borrelia, 20 belong to the Lyme disease group and are transmitted by ticks. All species that cause Lyme disease are referred to collectively as B. burgdorferi sensu lato, Twenty-five species of Borrelia are known to cause relapsing fever. While most species use the soft tick family Argasidae as their vector, some outliers live in hard ticks or lice. 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. Borellia miyamotoi disease B. miyamotoi is different from other relapsing-fever species in that it can also be spread by the same hard-shell Ixodes tick that spread Lyme disease. Other species are spread by the softbody Ornithodoros tick. == 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. Spirochetes can also be seen using Wright-stained blood smears. ==See also==