Lyme disease microbiology
Lyme disease, or borreliosis, is caused by spirochetal bacteria from the genus Borrelia, which has at least 37 known species, 12 of which are Lyme related, and an unknown number of genomic strains. Borrelia species known to cause Lyme disease are collectively known as Borrelia burgdorferi sensu lato.
Borrelia are microaerophilic and slow-growing—the primary reason for the long delays when diagnosing Lyme disease—and have been found to have greater strain diversity than previously estimated. The strains differ in clinical symptoms and/or presentation as well as geographic distribution.
Species and strains
Until recently, only three genospecies were thought to cause 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). Totally 10 complete genomes of B. burgdorferi sensu stricto, B. afzelii and B. garinii strains are available on NCBI Genome server at Feb 2013. B. burgdorferi strain B31 was derived by limited dilutional cloning from the original Lyme-disease tick isolate derived by Alan Barbour.
- 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 as east Asia.
Newly discovered genospecies have also been found to cause disease in humans:
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 Ixodes 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 southern tick-associated rash illness (STARI), also known as Masters disease in honor of its discoverer, Dr. Edwin Jordan Masters. The illness follows a lone star tick bite, and clinically resembles Lyme disease, but sufferers usually test negative for Lyme. Currently, no diagnostic test is available for STARI/Masters, and no official treatment protocol exists, though antibiotics are generally prescribed.
The number of reported cases of the borreliosis have been increasing, as are endemic regions in North America. Of cases reported to the United States Centers for Disease Control and Prevention (CDC), the rate of Lyme disease infection is 7.9 cases for every 100,000 persons. In the 10 states where Lyme disease is most common, the average was 31.6 cases per 100,000 persons for 2005. Although Lyme disease has now been reported in 49 of 50 states in the U.S (all but Hawaii), about 99% of all reported cases are confined to just five geographic areas (New England, Mid-Atlantic, East-North Central, South Atlantic, and West North-Central).
In Europe, cases of B. burgdorferi sensu lato-infected ticks are found predominantly in Norway, the Netherlands, Germany, France, Italy, Slovenia, and Poland, but have been isolated in almost every country on the continent. Lyme disease statistics for Europe can be found at Eurosurveillance website.
Borrelia burgdorferi sensu lato-infested ticks are being found more frequently in Japan, as well as in northwest China and far eastern Russia. Borrelia has been isolated in Mongolia as well.
In South America, tick-borne disease recognition and occurrence is rising. Ticks carrying B. burgdorferi sensu lato, as well as canine and human tick-borne diseases, have been reported widely in Brazil, but the subspecies of Borrelia has not yet been defined. The first reported case of Lyme disease in Brazil was made in 1993 in Sao Paulo. B. burgdorferi sensu stricto antigens in patients have been identified in Colombia and in Bolivia.
In western and sub-Saharan Africa, tick-borne relapsing fever has been recognized for over a century, since it was first isolated by the British physicians Joseph Everett Dutton and John Lancelot Todd in 1905. Borrelia in the manifestation of Lyme disease in this region is presently unknown, but evidence indicates the disease may occur in humans in sub-Saharan Africa. The abundance of hosts and tick vectors would favor the establishment of the infection in Africa. In East Africa two cases of Lyme disease have been reported in Kenya.
In Australia, no definitive evidence exists for the existence of B. burgdorferi or for any other tick-borne spirochete that may be responsible for a local syndrome being reported as Lyme disease. Cases of neuroborreliosis have been documented in Australia, but are often ascribed to travel to other continents. The existence of Lyme disease in Australia is controversial.
The lifecycle of B. burgdorferi is complex, requiring ticks, rodents, and deer at various points. Mice are the primary reservoir for the bacteria; Ixodes ticks then transmit the B. burgdorferi infection to deer.
Hard ticks have a variety of life histories with respect to optimizing their chance of contact with an appropriate host to ensure survival. The life stages of soft ticks are not readily distinguishable. The first stage to hatch from the egg, a six-legged larva, takes a blood meal from a host, and molts to the first nymphal stage. Unlike hard ticks, many soft ticks go through multiple nymphal stages, gradually increasing in size until the final molt to the adult stage.
The lifecycle concept encompassing reservoirs and infections in multiple hosts has recently been expanded to encompass forms of the spirochete which differ from the motile corkscrew form, and these include cystic spheroplast-like forms, straight uncoiled bacillary forms which are immotile due to flagellin mutations, and granular forms, coccoid in profile. The model of Plasmodium species malaria, with multiple parasitic profiles demonstrable in various host insects and mammals, is a hypothesized model for a similarly complex proposed Borrelia spirochete lifecycle.
Whereas B. burgdorferi is most associated with deer ticks and the white footed mouse, B. afzelli is most frequently detected in rodent-feeding vector ticks, and B. garinii and B. valaisiana appear to be associated with birds. Both rodents and birds are competent reservoir hosts for B. burgdorferi sensu stricto. The resistance of a genospecies of Lyme disease spirochetes to the bacteriolytic activities of the alternative immune complement system of various host species may determine its reservoir host association.
The genome of B. burgdorferi (B31 strain) was the third microbial genome ever to be sequenced, following the sequencing of both H. influenzae and M. genitalium in 1995, and its chromosome contains 910,725 base pairs and 853 genes. One of the most striking features of B. burgdorferi as compared with other bacteria is its unusual genome, which is far more complex than that of its spirochetal cousin Treponema pallidum, the agent of syphilis. In addition to a linear chromosome, the genome of B. burgdorferi strain B31 includes 21 plasmids (12 linear and 9 circular) – by far the largest number of plasmids found in any known bacterium. Genetic exchange, including plasmid transfers, contributes to the pathogenicity of the organism. Long-term culture of B. burgdorferi results in a loss of some plasmids and changes in expressed protein profiles. Associated with the loss of plasmids is a loss in the ability of the organism to infect laboratory animals, suggesting the plasmids encode key genes involved in virulence.
Chemical analysis of the external membrane of B. burgdorferi revealed the presence of 46% proteins, 51% lipids and 3% carbohydrates.
Structure and growth
B. burgdorferi is a highly specialized, motile, two-membrane, flat-waved spirochete, ranging from about 9 to 32 micrometers in length. Because of its double-membrane envelope, it is often mistakenly described as Gram negative, though it stains weakly in Gram stain. The bacterial membranes in at least the B31, NL303 and N40 strains of B. burgdorferi do not contain lipopolysaccharide, which is extremely atypical for Gram negative bacteria; instead, the membranes contain glycolipids. However, the membranes in the B31 strain have been found to contain a lipopolysaccharide-like component. B. burgdorferi is a microaerophilic organism, requiring little oxygen to survive. Unlike most bacteria, B. burgdorferi does not use iron, hence avoiding the difficulty of acquiring iron during infection. It lives primarily as an extracellular pathogen, although in vitro it can also hide intracellularly (see Mechanisms of persistence section).
Like other spirochetes, such as Treponema pallidum (the agent of syphilis), B. burgdorferi has an axial filament composed of flagella which run lengthways between its cell wall and outer membrane. This structure allows the spirochete to move efficiently in corkscrew fashion through viscous media, such as connective tissue.
B. burgdorferi is very slow growing, with a doubling time of 12–18 hours (in contrast to pathogens such as Streptococcus and Staphylococcus, which have a doubling time of 20–30 minutes). Since most antibiotics kill bacteria only when they are dividing, this longer doubling time necessitates the use of relatively longer treatment courses for Lyme disease.
Outer surface proteins
The outer membrane of B. burgdorferi is composed of various unique outer surface proteins (Osp) that have been characterized (OspA through OspF). The Osp proteins are lipoproteins anchored by N-terminally attached fatty acid molecules to the membrane. They are presumed to play a role in virulence, transmission, or survival in the tick.
OspA, OspB, and OspD are expressed by B. burgdorferi residing in the gut of unfed ticks, suggesting they promote the persistence of the spirochete in ticks between blood meals. During transmission to the mammalian host, when the nymphal tick begins to feed and the spirochetes in the midgut begin to multiply rapidly, most spirochetes cease expressing OspA on their surfaces. Simultaneous with the disappearance of OspA, the spirochete population in the midgut begins to express an OspC and migrates to the salivary gland. Upregulation of OspC begins during the first day of feeding and peaks 48 hours after attachment.
The OspA and OspB genes encode the major outer membrane proteins of B. burgdorferi. The two Osp proteins show a high degree of sequence similarity, indicating a recent duplication event. Virtually all spirochetes in the midgut of an unfed nymph tick express OspA. OspA promotes the attachment of B. burgdorferi to the tick protein TROSPA, present on tick gut epithelial cells. OspB also has an essential role in the adherence of B. burgdorferi to the tick gut. Although OspD has been shown to bind to tick gut extracts in vitro, as well as OspA and OspB, it is not essential for the attachment and colonization of the tick gut, and it is not required for human infections.
OspC is a strong antigen; detection of its presence by the host organism stimulates an immune response. While each individual bacterial cell contains just one copy of the ospC gene, the gene sequence of ospC among different strains within each of the three major Lyme disease species is highly variable. OspC plays an essential role during the early stage of mammalian infection. In infected ticks feeding on a mammalian host, OspC may also be necessary to allow B. burgdorferi to invade and attach to the salivary gland after leaving the gut, although not all studies agree on such a role for the protein. OspC attaches to the tick salivary protein Salp15, which protects the spirochete from complement and impairs the function of dendritic cells.
OspE and OspF were initially identified in B. burgdorferi strain N40. The ospE and ospF genes are structurally arranged in tandem as one transcriptional unit under the control of a common promoter. Individual strains of B. burgdorferi carry multiple related copies of the ospEF locus, which are now collectively referred to as Erp (Osp'E'/F-like 'r'elated 'p'rotein) genes. In B. burgdoreri strains B31 and 297, most of the Erp loci occupy the same position on the multiple copies of the cp32 plasmid present in these strains. Each locus consists of one or two Erp genes. When two genes are present, they are transcribed as one operon, although in some cases, an internal promoter in the first gene may also transcribe the second gene. The presence of multiple Erp proteins was proposed to be important in allowing B. burgdorferi to evade killing by the alternative complement pathway of a broad range of potential animal hosts, as individual Erp proteins exhibited different binding patterns to the complement regulator factor H from different animals. However, the presence of factor H was recently demonstrated to not be necessary to enable B. burgdorferi to infect mice, suggesting the Erp proteins have an additional function.
Mechanisms of persistence
While B. burgdorferi is susceptible to a number of antibiotics in vitro, reports are contradictory as to the efficacy of antibiotics in vivo. B. burgdorferi may persist in humans and animals for months or years. Some studies have suggested persistence of infection despite antibiotic therapy, although others suggested antibiotics rapidly end infections.
Various survival strategies of B. burgdorferi have been posited to explain how the pathogen can persist in its host. including the following:
- Physical sequestration of B. burgdorferi in sites less accessible to the immune system and antibiotics, such as the brain and central nervous system. New evidence suggests that B. burgdorferi may use the host's fibrinolytic system to penetrate the blood–brain barrier.
- Intracellular invasion
B. burgdorferi can invade a variety of cultured cells, including endothelium, fibroblasts, lymphocytes, macrophages, keratinocytes, synovium, and most recently neuronal and glial cells. By 'hiding' inside these cells during human infection, B. burgdorferi may be able to evade the immune system and be protected to varying degrees against some antibiotics, sometimes allowing the infection to persist. However it remains unknown whether the in vitro observations made with cultured cells are relevant to persistent infection in Lyme disease patients as there have been few reports of intracellular B. burgdorferi in vivo.
The formation of rounded forms of B. burgdorferi cells, sometimes called 'spheroplasts', which either lack a cell wall or have a damaged cell wall, has been observed in vitro, in vivo, and in an ex vivo model. The finding that energy is required for the spiral bacterium to convert to this form suggests these altered forms have a survival function, and are not merely end-stage degeneration products. Some data suggest these rounded cells are virulent and infectious, are able to survive under adverse environmental conditions, and may revert to the spiral form in vitro, once conditions are more favorable. However, rounded cell types triggered by an antibody binding to the OspB surface protein are damaged and dying forms of the bacteria and do not represent a separate form of the organism.
Compared to the spiral form, spheroplasts of B. burgdorferi have reduced surface area exposed to immune surveillance. They also express some different surface proteins from spirochetes. B. burgdorferi spheroplasts have shown sensitivity in vitro to antiparasitic drugs, such as metronidazole, tinidazole, and hydroxychloroquine  to which the spiral form of B. burgdorferi is not sensitive.
Like the Borrelia that causes relapsing fever, B. burgdorferi has the ability to vary its surface proteins in response to immune attack. This ability is related to the genomic complexity of B. burgdorferi, and is another way B. burgdorferi evades the immune system to establish a chronic infection.
- Immune system suppression
Complement inhibition, induction of anti-inflammatory cytokines such as IL-10, and the formation of immune complexes have all been documented in B. burgdorferi infection. Furthermore, the existence of immune complexes may be involved in seronegative acute-phase disease (i.e. false-negative antibody tests of blood and cerebrospinal fluid). One study shows some acute-phase seronegative Lyme patients have antibodies bound up in these complexes.
Advancing immunology research
The role of T cells in Borrelia was first made in 1984, the role of cellular immunity in active Lyme disease was made in 1986, and long-term persistence of T cell lymphocyte responses to B. burgdorferi as an "immunological scar syndrome" was hypothesized in 1990. The role of Th1 and interferon-gamma (IFN-gamma) in Borrelia was first described in 1995. The cytokine pattern of Lyme disease, and the role of Th1 with down-regulation of interleukin-10 (IL-10) was first proposed in 1997.
Recent studies in both acute and antibiotic refractory, or chronic, Lyme disease have shown a distinct proinflammatory immune process. This proinflammatory process is a cell-mediated immunity and results in Th1 up-regulation. These studies have shown a significant decrease in cytokine output of (IL-10), an up-regulation of interleukin-6 and interleukin-12 and interferon-gamma and dysregulation in TNF-alpha,` predominantly.
New research has also found chronic Lyme patients have higher amounts of Borrelia-specific FoxP3 than healthy controls, indicating regulatory T cells might also play a role, by immunosuppression, in the development of chronic Lyme disease. FoxP3 is a specific marker of regulatory T cells. The signaling pathway P38 mitogen-activated protein kinases (p38 MAP kinase) has also been identified as promoting expression of proinflammatory cytokines from borrelia.
The culmination of these new and ongoing immunological studies suggests this cell-mediated immune disruption in the Lyme patient amplifies the inflammatory process, often rendering it chronic and self-perpetuating, regardless of whether the Borrelia bacterium is still present in the host, or in the absence of the inciting pathogen in an autoimmune pattern.
A vaccine based on the surface protein OspA (LYMErix; SmithKline Beecham) was licensed for use in adults. However, the manufacturer voluntarily removed the vaccine from the market in 2002. The current focus is on vaccine candidates that require fewer boosts and provide long-term protection. Interest is developing in vaccines that specifically target the tick vectors of Lyme disease, specifically components of tick saliva that coat the bacteria. This approach offers the advantage of protecting against multiple pathogens with one vaccine. While an effective Lyme disease vaccine seems likely to be developed, earlier experiences with the LYMErix vaccine suggest bringing such a vaccine to market will be a challenge.
A vaccine made by Pfizer, known as LymeVax, is currently available for use in dogs. Having dogs vaccinated should also help to protect their owners from infection by the dogs. It is a two-strain, multiantigen vaccine which induces an antibody response to bacterial proteins OspA and OspC.
- Samuels DS; Radolf, JD (editors) (2010). Borrelia: Molecular Biology, Host Interaction and Pathogenesis. Caister Academic Press. ISBN 978-1-904455-58-5.
- Bunikis J, Garpmo U, Tsao J, Berglund J, Fish D, Barbour AG; Garpmo; Tsao; Berglund; Fish; Barbour (2004). "Sequence typing reveals extensive strain diversity of the Lyme borreliosis agents Borrelia burgdorferi in North America and Borrelia afzelii in Europe" (PDF). Microbiology 150 (Pt 6): 1741–55. doi:10.1099/mic.0.26944-0. PMID 15184561.
- Ryan KJ, Ray CG (editors) (2004). Sherris Medical Microbiology (4th ed.). McGraw Hill. ISBN 0-8385-8529-9.
- Felsenfeld O (1971). Borrelia: Strains, Vectors, Human and Animal Borreliosis. St. Louis: Warren H. Green, Inc.
- Wang G; van Dam AP; Le Fleche A et al. (1997). "Genetic and phenotypic analysis of Borrelia valaisiana sp. nov. (Borrelia genomic groups VS116 and M19)". Int. J. Syst. Bacteriol. 47 (4): 926–932. doi:10.1099/00207713-47-4-926. PMID 9336888.
- Diza E, Papa A, Vezyri E, Tsounis S, Milonas I, Antoniadis A; Papa; Vezyri; Tsounis; Milonas; Antoniadis (2004). "Borrelia valaisiana in cerebrospinal fluid". Emerging Infect. Dis. 10 (9): 1692–3. doi:10.3201/eid1009.030439. PMC 3320289. PMID 15503409.
- Masuzawa T (2004). "Terrestrial distribution of the Lyme borreliosis agent Borrelia burgdorferi sensu lato in East Asia". Jpn. J. Infect. Dis. 57 (6): 229–235. PMID 15623946.
- Collares-Pereira M, Couceiro S, Franca I, Kurtenbach K, Schafer SM, Vitorino L, Goncalves L, Baptista S, Vieira ML, Cunha C; Couceiro; Franca; Kurtenbach; Schäfer; Vitorino; Gonçalves; Baptista; Vieira; Cunha (2004). "First isolation of Borrelia lusitaniae from a human patient" (PDF). J Clin Microbiol 42 (3): 1316–8. doi:10.1128/JCM.42.3.1316-1318.2004. PMC 356816. PMID 15004107.
- Postic D, Ras NM, Lane RS, Hendson M, Baranton G; Ras; Lane; Hendson; Baranton (1998). "Expanded diversity among Californian Borrelia isolates and description of Borrelia bissettii sp. nov. (formerly Borrelia group DN127)" (PDF). J Clin Microbiol 36 (12): 3497–3504. PMC 105228. PMID 9817861.
- Maraspin V, Cimperman J, Lotric-Furlan S, Ruzic-Sabljic E, Jurca T, Picken RN, Strle F; Cimperman; Lotric-Furlan; Ruzić-Sabljić; Jurca; Picken; Strle (2002). "Solitary borrelial lymphocytoma in adult patients". Wien Klin Wochenschr 114 (13–14): 515–523. PMID 12422593.
- Richter D, Postic D, Sertour N, Livey I, Matuschka FR, Baranton G; Postic; Sertour; Livey; Matuschka; Baranton (2006). "Delineation of Borrelia burgdorferi sensu lato species by multilocus sequence analysis and confirmation of the delineation of Borrelia spielmanii sp. nov". Int J Syst Evol Microbiol 56 (Pt 4): 873–881. doi:10.1099/ijs.0.64050-0. PMID 16585709.
- Foldvari G, Farkas R, Lakos A; Farkas; Lakos (2005). "Borrelia spielmanii erythema migrans, Hungary". Emerg Infect Dis 11 (11): 1794–5. doi:10.3201/eid1111.050542. PMC 3367353. PMID 16422006.
- Scoles GA, Papero M, Beati L, Fish D (2001). "A relapsing fever group spirochete transmitted by Ixodes scapularis ticks". Vector-Borne and Zoonotic Diseases 1 (1): 21–34. doi:10.1089/153036601750137624. PMID 12653133.
- Bunikis J, Tsao J, Garpmo U, Berglund J, Fish D, Barbour AG (2004). "Typing of Borrelia relapsing fever group strains". Emerg Infect Dis 10 (9): 1661–4. doi:10.3201/eid1009.040236. PMC 3320305. PMID 15498172.
- McNeil, Donald (19 September 2011). "New Tick-Borne Disease Is Discovered". The New York Times. pp. D6. Retrieved 20 September 2011.
- Varela AS, Luttrell MP, Howerth EW, Moore VA, Davidson WR, Stallknecht DE, Little SE (2004). "First culture isolation of Borrelia lonestari, putative agent of southern tick-associated rash illness" (PDF). J Clin Microbiol 42 (3): 1163–9. doi:10.1128/JCM.42.3.1163-1169.2004. PMC 356874. PMID 15004069.
- Masters E, Granter S, Duray P, Cordes P (1998). "Physician-diagnosed erythema migrans and erythema migrans-like rashes following Lone Star tick bites". Arch Dermatol 134 (8): 955–960. doi:10.1001/archderm.134.8.955. PMID 9722725.
- Grubhoffer L, Golovchenko M, Vancova M, Zacharovova-Slavickova K, Rudenko N, Oliver JH Jr. (November 2005). "Lyme borreliosis: insights into tick-/host-borrelia relations". Folia Parasitol (Praha) 52 (4 (Review)): 279–294. PMID 16405291.
- Higgins R (August 2004). "Emerging or re-emerging bacterial zoonotic diseases: bartonellosis, leptospirosis, Lyme borreliosis, plague". Rev Sci Tech. 23 (2): 569–581. PMID 15702720.
- "DVBID: Disease Upward Climb – CDC Lyme Disease". 2006-10-02. Retrieved 2007-08-23.
- "Lyme Disease Statistics". Centers for Disease Control and Prevention (CDC). 2007-04-02. Retrieved 2007-08-23.
- Li M, Masuzawa T, Takada N, Ishiguro F, Fujita H, Iwaki A, Wang H, Wang J, Kawabata M, Yanagihara Y (July 1998). "Lyme disease Borrelia species in northeastern China resemble those isolated from far eastern Russia and Japan". Appl Environ Microbiol 64 (7): 2705–9. PMC 106449. PMID 9647853.
- Masuzawa T (December 2004). "Terrestrial distribution of the Lyme borreliosis agent Borrelia burgdorferi sensu lato in East Asia". Jpn J Infect Dis. 57 (6): 229–235. PMID 15623946.
- Walder G, Lkhamsuren E, Shagdar A, Bataa J, Batmunkh T, Orth D, Heinz FX, Danichova GA, Khasnatinov MA, Wurzner R, Dierich MP (May 2006). "Serological evidence for tick-borne encephalitis, borreliosis, and human granulocytic anaplasmosis in Mongolia". Int J Med Microbiol. 296 (Suppl 40): 69–75. doi:10.1016/j.ijmm.2006.01.031. PMID 16524782.
- Mantovani E, Costa IP, Gauditano G, Bonoldi VL, Higuchi ML, Yoshinari NH (April 2007). "Description of Lyme disease-like syndrome in Brazil: is it a new tick-borne disease or Lyme disease variation?". Braz J Med Biol Res. 40 (4): 443–456. doi:10.1590/S0100-879X2006005000082. PMID 17401487.
- Yoshinari NH, Oyafuso LK, Monteiro FG, de Barros PJ, da Cruz FC, Ferreira LG, Bonasser F, Baggio D, Cossermelli W (Jul–Aug 1993). "Lyme disease. Report of a case observed in Brazil". Rev Hosp Clin Fac Med Sao Paulo 48 (4): 170–4. PMID 8284588.
- Bouattour A, Ghorbel A, Chabchoub A, Postic D (2004). "Lyme borreliosis situation in North Africa". Arch Inst Pasteur Tunis. 81 (1–4): 13–20. PMID 16929760.
- Dsouli N, Younsi-Kabachii H, Postic D, Nouira S, Gern L, Bouattour A (July 2006). "Reservoir role of lizard Psammodromus algirus in transmission cycle of Borrelia burgdorferi sensu lato (Spirochaetaceae) in Tunisia". Journal of Medical Entomology 43 (4): 737–742. doi:10.1603/0022-2585(2006)43[737:RROLPA]2.0.CO;2. ISSN 0022-2585. PMID 16892633.
- Helmy N (August 2000). "Seasonal abundance of Ornithodoros (O.) savignyi and prevalence of infection with Borrelia spirochetes in Egypt". J Egypt Soc Parasitol 30 (2): 607–619. PMID 10946521.
- Fivaz BH, Petney TN (September 1989). "Lyme disease — a new disease in southern Africa?". J S Afr Vet Assoc. 60 (3): 155–8. PMID 2699499.
- Jowi JO, Gathua SN (May 2005). "Lyme disease: report of two cases". East Afr Med J. 82 (5): 267–9. doi:10.4314/eamj.v82i5.9318. PMID 16119758.
- Piesman J, Stone BF (February 1991). "Vector competence of the Australian paralysis tick, Ixodes holocyclus, for the Lyme disease spirochete Borrelia burgdorferi". Int J Parasitol. 21 (1): 109–111. doi:10.1016/0020-7519(91)90127-S. PMID 2040556.
- "Lyme: a four letter word". ABC Radio National Background Briefing. Australian Broadcasting Corporation. 12 May 2013. Retrieved 12 May 2013.
- Macdonald AB (2006). "A life cycle for Borrelia spirochetes?". Med Hypotheses 67 (4): 810–8. doi:10.1016/j.mehy.2006.03.028. PMID 16716532.
- "Lymeinfo.net — LDAdverseConditions" (PDF). 2006.
- Wallis RC, Brown SE, Kloter KO, Main AJ Jr. (October 1978). "Erythema chronicum migrans and Lyme arthritis: field study of ticks". Am J Epidemiol. 108 (4): 322–7. PMID 727201.
- Fraser, Claire M.; Casjens, S; Huang, WM; Sutton, GG; Clayton, R; Lathigra, R; White, O; Ketchum, KA et al. (1997). "Genomic sequence of a Lyme disease spirochaete, Borrelia burgdorferi". Nature 390 (6660): 580–6. doi:10.1038/37551. PMID 9403685.
- Porcella SF, Schwan TG (2001). "Borrelia burgdorferi and Treponema pallidum: a comparison of functional genomics, environmental adaptations, and pathogenic mechanisms". J Clin Invest 107 (6): 651–6. doi:10.1172/JCI12484. PMC 208952. PMID 11254661.
- Casjens S, Palmer N, van Vugt R, Huang WM, Stevenson B, Rosa P, Lathigra R, Sutton G, Peterson J, Dodson RJ, Haft D, Hickey E, Gwinn M, White O, Fraser CM (2000). "A bacterial genome in flux: the twelve linear and nine circular extrachromosomal DNAs in an infectious isolate of the Lyme disease spirochete Borrelia burgdorferi". Mol Microbiol 35 (3): 490–516. doi:10.1046/j.1365-2958.2000.01698.x. PMID 10672174.
- Qiu WG, Schutzer SE, Bruno JF, Attie O, Xu Y, Dunn JJ, Fraser CM, Casjens SR, Luft BJ (2004). "Genetic exchange and plasmid transfers in Borrelia burgdorferi sensu stricto revealed by three-way genome comparisons and multilocus sequence typing" (PDF). Proc Natl Acad Sci USA 101 (39): 14150–5. doi:10.1073/pnas.0402745101. PMC 521097. PMID 15375210.
- Schwarzová K (June 1993). "Lyme borreliosis: review of present knowledge". Cesk Epidemiol Mikrobiol Imunol. 42 (2): 87–92. PMID 8348630.
- Goldstein SF, Charon NW, Kreiling JA (1994). "Borrelia burgdorferi swims with a planar waveform similar to that of eukaryotic flagella". Proc. Natl. Acad. Sci. U.S.A. 91 (8): 3433–7. doi:10.1073/pnas.91.8.3433. PMC 43591. PMID 8159765.
- Samuels DS; Radolf, JD (editors) (2010). "Ch. 6: Structure, Function and Biogenesis of the Borrelia Cell Envelope". Borrelia: Molecular Biology, Host Interaction and Pathogenesis. Caister Academic Press. ISBN 978-1-904455-58-5.
- Ben-Menachem G, Kubler-Kielb J, Coxon B, Yergey A, Schneerson R (2003). "A newly discovered cholesteryl galactoside from Borrelia burgdorferi". Proc. Natl. Acad. Sci. U.S.A. 100 (13): 7913–8. doi:10.1073/pnas.1232451100. PMC 164687. PMID 12799465.
- Schwarzová K, Čižnár I (2004). "Immunochemical analysis of lipopolysaccharide-like component extracted from Borrelia burgdorferi sensu lato" (PDF). Folia Microbiol. 49 (5): 625–9. doi:10.1007/BF02931545. Retrieved 2007-10-26.
- Posey JE, Gherardini FC (2000). "Lack of a role for iron in the Lyme disease pathogen". Science 288 (5471): 1651–3. doi:10.1126/science.288.5471.1651. PMID 10834845.
- Kelly, RT (1984). Krieg NR, Holt JG, ed. Genus IV. Borrelia Swellengrebel 1907, 582AL 1. Williams & Wilkins: Baltimore. pp. 57–62.
- Haake DA (2000). "Spirochaetal lipoproteins and pathogenesis". Microbiology (Reading, Engl.) 146 (7): 1491–1504. PMC 2664406. PMID 10878114.
- Schwan TG, Piesman J, Golde WT, Dolan MC, Rosa PA (1995). "Induction of an outer surface protein on Borrelia burgdorferi during tick feeding". Proc. Natl. Acad. Sci. U.S.A. 92 (7): 2909–13. doi:10.1073/pnas.92.7.2909. PMC 42328. PMID 7708747.
- Li X, Neelakanta G, Liu X, Beck DS, Kantor FS, Fish D, Anderson JF, Fikrig E (2007). "Role of outer surface protein D in the Borrelia burgdorferi life cycle". Infect. Immun. 75 (9): 4237–44. doi:10.1128/IAI.00632-07. PMC 1951184. PMID 17620358.
- Schwan TG, Piesman J (2000). "Temporal changes in outer surface proteins A and C of the Lyme disease-associated spirochete, Borrelia burgdorferi, during the chain of infection in ticks and mice". J Clin Microbiol 38 (1): 382–8. PMC 88728. PMID 10618120.
- Bergström S, Bundoc VG, Barbour AG (1989). "Molecular analysis of linear plasmid-encoded major surface proteins, OspA and OspB, of the Lyme disease spirochaete Borrelia burgdorferi". Mol. Microbiol. 3 (4): 479–486. doi:10.1111/j.1365-2958.1989.tb00194.x. PMID 2761388.
- Pal U, Li X, Wang T, Montgomery RR, Ramamoorthi N, Desilva AM, Bao F, Yang X, Pypaert M, Pradhan D, Kantor FS, Telford S, Anderson JF, Fikrig E (2004). "TROSPA, an Ixodes scapularis receptor for Borrelia burgdorferi". Cell 119 (4): 457–468. doi:10.1016/j.cell.2004.10.027. PMID 15537536.
- Neelakanta G, Li X, Pal U, Liu X, Beck DS, DePonte K, Fish D, Kantor FS, Fikrig E (2007). "Outer surface protein B is critical for Borrelia burgdorferi adherence and survival within Ixodes ticks". PLoS Pathog. 3 (3): e33. doi:10.1371/journal.ppat.0030033. PMC 1817655. PMID 17352535.
- Baranton G, Seinost G, Theodore G, Postic D, Dykhuizen D (March 2001). "Distinct levels of genetic diversity of Borrelia burgdorferi are associated with different aspects of pathogenicity". Res. Microbiol. 152 (2): 149–56. doi:10.1016/S0923-2508(01)01186-X. PMID 11316368.
- Tilly K, Krum JG, Bestor A, Jewett MW, Grimm D, Bueschel D, Byram R, Dorward D, Vanraden MJ, Stewart P, Rosa P (June 2006). "Borrelia burgdorferi OspC protein required exclusively in a crucial early stage of mammalian infection". Infect. Immun. 74 (6): 3554–64. doi:10.1128/IAI.01950-05. PMC 1479285. PMID 16714588.
- Pal U, Yang X, Chen M, Bockenstedt LK, Anderson JF, Flavell RA, Norgard MV, Fikrig E (January 2004). "OspC facilitates Borrelia burgdorferi invasion of Ixodes scapularis salivary glands". J. Clin. Invest. 113 (2): 220–30. doi:10.1172/JCI19894. PMC 311436. PMID 14722614.
- Grimm D, Tilly K, Byram R, Stewart PE, Krum JG, Bueschel DM, Schwan TG, Policastro PF, Elias AF, Rosa PA (March 2004). "Outer-surface protein C of the Lyme disease spirochete: a protein induced in ticks for infection of mammals". Proc. Natl. Acad. Sci. U.S.A. 101 (9): 3142–7. doi:10.1073/pnas.0306845101. PMC 365757. PMID 14970347.
- Ramamoorthi N, Narasimhan S, Pal U, Bao F, Yang XF, Fish D, Anguita J, Norgard MV, Kantor FS, Anderson JF, Koski RA, Fikrig E (July 2005). "The Lyme disease agent exploits a tick protein to infect the mammalian host". Nature 436 (7050): 573–7. doi:10.1038/nature03812. PMID 16049492.
- Schuijt TJ, Hovius JW, van Burgel ND, Ramamoorthi N, Fikrig E, van Dam AP (July 2008). "The tick salivary protein Salp15 inhibits the killing of serum-sensitive Borrelia burgdorferi sensu lato isolates". Infect. Immun. 76 (7): 2888–94. doi:10.1128/IAI.00232-08. PMC 2446733. PMID 18426890.
- Hovius JW, de Jong MA, den Dunnen J, Litjens M, Fikrig E, van der Poll T, Gringhuis SI, Geijtenbeek TB (February 2008). "Salp15 binding to DC-SIGN inhibits cytokine expression by impairing both nucleosome remodeling and mRNA stabilization". PLoS Pathog. 4 (2): e31. doi:10.1371/journal.ppat.0040031. PMC 2242833. PMID 18282094.
- Lam TT, Nguyen TP, Montgomery RR, Kantor FS, Fikrig E, Flavell RA (1994). "Outer surface proteins E and F of Borrelia burgdorferi, the agent of Lyme disease". Infect. Immun. 62 (1): 290–8. PMC 186099. PMID 8262642.
- Stevenson B, Zückert WR, Akins DR (2000). "Repetition, conservation, and variation: the multiple cp32 plasmids of Borrelia species". J. Mol. Microbiol. Biotechnol. 2 (4): 411–422. PMID 11075913.
- Stevenson B, Bono JL, Schwan TG, Rosa P (1998). "Borrelia burgdorferi Erp proteins are immunogenic in mammals infected by tick bite, and their synthesis is inducible in cultured bacteria". Infect. Immun. 66 (6): 2648–54. PMC 108251. PMID 9596729.
- Stevenson B, El-Hage N, Hines MA, Miller JC, Babb K (2002). "Differential binding of host complement inhibitor factor H by Borrelia burgdorferi Erp surface proteins: a possible mechanism underlying the expansive host range of Lyme disease spirochetes". Infect. Immun. 70 (2): 491–7. doi:10.1128/IAI.70.2.491-497.2002. PMC 127719. PMID 11796574.
- Woodman ME, Cooley AE, Miller JC, Lazarus JJ, Tucker K, Bykowski T, Botto M, Hellwage J, Wooten RM, Stevenson B (2007). "Borrelia burgdorferi binding of host complement regulator factor H is not required for efficient mammalian infection". Infect. Immun. 75 (6): 3131–9. doi:10.1128/IAI.01923-06. PMC 1932899. PMID 17420242.
- Bayer ME, Zhang L, Bayer MH (1996). "Borrelia burgdorferi DNA in the urine of treated patients with chronic Lyme disease symptoms. A PCR study of 97 cases". Infection 24 (5): 347–353. doi:10.1007/BF01716077. PMID 8923044.
- Preac-Mursic V; Weber K; Pfister HW et al. (1989). "Survival of Borrelia burgdorferi in antibiotically treated patients with Lyme borreliosis". Infection 17 (6): 355–9. doi:10.1007/BF01645543. PMID 2613324.
- Oksi J, Marjamaki M, Nikoskelainen J, Viljanen MK (1999). "Borrelia burgdorferi detected by culture and PCR in clinical relapse of disseminated Lyme borreliosis". Annals of Medicine 31 (3): 225–232. doi:10.3109/07853899909115982. PMID 10442678.
- Nadelman RB; Nowakowski J; Forseter G et al. (June 1993). "Failure to isolate Borrelia burgdorferi after antimicrobial therapy in culture-documented Lyme borreliosis associated with erythema migrans: report of a prospective study". Am. J. Med. 94 (6): 583–8. doi:10.1016/0002-9343(93)90208-7. PMID 8506882.
- Muellegger RR; Zoechling N; Soyer HP et al. (June 1995). "No detection of Borrelia burgdorferi-specific DNA in erythema migrans lesions after minocycline treatment". Arch Dermatol 131 (6): 678–82. doi:10.1001/archderm.131.6.678. PMID 7778919.
- Embers ME, Ramamoorthy R, Philipp MT (2004). "Survival strategies of Borrelia burgdorferi, the etiologic agent of Lyme disease". Microbes Infect 6 (3): 312–318. doi:10.1016/j.micinf.2003.11.014. PMID 15065567.
- Miklossy J; Khalili K; Gern L et al. (2004). "Borrelia burgdorferi persists in the brain in chronic Lyme neuroborreliosis and may be associated with Alzheimer disease". J Alzheimers Dis 6 (6): 639–649; discussion 673–681. PMID 15665404.
- Grab DJ, Perides G, Dumler JS, Kim KJ, Park J, Kim YV, Nikolskaia O, Choi KS, Stins MF, Kim KS (2005). "Borrelia burgdorferi, host-derived proteases, and the blood–brain barrier". Infect Immun 73 (2): 1014–1022. doi:10.1128/IAI.73.2.1014-1022.2005. PMC 546937. PMID 15664945.
- Ma Y, Sturrock A, Weis JJ (1991). "Intracellular localization of Borrelia burgdorferi within human endothelial cells". Infect Immun 59 (2): 671–678. PMC 257809. PMID 1987083.
- Klempner MS, Noring R, Rogers RA (1993). "Invasion of human skin fibroblasts by the Lyme disease spirochete, Borrelia burgdorferi". J Infect Dis 167 (5): 1074–1081. doi:10.1093/infdis/167.5.1074. PMID 8486939.
- Dorward DW, Fischer ER, Brooks DM (1997). "Invasion and cytopathic killing of human lymphocytes by spirochetes causing Lyme disease". Clin Infect Dis 25 (Suppl 1): S2–8. doi:10.1086/516169. PMID 9233657.
- Montgomery RR, Nathanson MH, Malawista SE (1993). "The fate of Borrelia burgdorferi, the agent for Lyme disease, in mouse macrophages. Destruction, survival, recovery". Journal of Immunology 150 (3): 909–915. PMID 8423346.
- Aberer E, Kersten A, Klade H, Poitschek C, Jurecka W (August 12–19, 2005). "Heterogeneity of Borrelia burgdorferi in the skin". Neurosci Lett. 384 (1–2): 112–116. doi:10.1016/j.neulet.2005.04.069. PMID 15893422.
- Girschick HJ, Huppertz HI, Russmann H, Krenn V, Karch H (1996). "Intracellular persistence of Borrelia burgdorferi in human synovial cells". Rheumatol Int 16 (3): 125–132. doi:10.1007/BF01409985. PMID 8893378.
- Nanagara R, Duray PH, Schumacher HR Jr (1996). "Ultrastructural demonstration of spirochetal antigens in synovial fluid and synovial membrane in chronic Lyme disease: possible factors contributing to persistence of organisms". Hum Pathol 27 (10): 1025–1034. doi:10.1016/S0046-8177(96)90279-8. PMID 8892586.
- Livengood JA, Gilmore RD (2006). "Invasion of human neuronal and glial cells by an infectious strain of Borrelia burgdorferi". Microbes Infect 8 (14–15): 2832–40. doi:10.1016/j.micinf.2006.08.014. PMID 17045505.
- Georgilis K, Peacocke M, Klempner MS (1992). "Fibroblasts protect the Lyme disease spirochete, Borrelia burgdorferi, from ceftriaxone in vitro". J Infect Dis 166 (2): 440–444. doi:10.1093/infdis/166.2.440. PMID 1634816.
- Brouqui P, Badiaga S, Raoult D (1996). "Eucaryotic cells protect Borrelia burgdorferi from the action of penicillin and ceftriaxone but not from the action of doxycycline and erythromycin" (PDF). Antimicrob Agents Chemother 40 (6): 1552–1554. PMC 163368. PMID 8726038.
- Alban PS, Johnson PW, Nelson DR (1 January 2000). "Serum-starvation-induced changes in protein synthesis and morphology of Borrelia burgdorferi". Microbiology 146 (1): 119–127. PMID 10658658.
- Mursic VP; Wanner G; Reinhardt S et al. (1996). "Formation and cultivation of Borrelia burgdorferi spheroplast-L-form variants". Infection 24 (3): 218–226. doi:10.1007/BF01781096. PMID 8811359.
- Kersten A, Poitschek C, Rauch S, Aberer E (1995). "Effects of penicillin, ceftriaxone, and doxycycline on morphology of Borrelia burgdorferi" (PDF). Antimicrob Agents Chemother 39 (5): 1127–1133. doi:10.1128/aac.39.5.1127. PMC 162695. PMID 7625800.
- Schaller M, Neubert U (1994). "Ultrastructure of Borrelia burgdorferi after exposure to benzylpenicillin". Infection 22 (6): 401–406. doi:10.1007/BF01715497. PMID 7698837.
- Phillips SE, Mattman LH, Hulinska D, Moayad H (1998). "A proposal for the reliable culture of Borrelia burgdorferi from patients with chronic Lyme disease, even from those previously aggressively treated". Infection 26 (6): 364–367. doi:10.1007/BF02770837. PMID 9861561.
- Duray PH; Yin SR; Ito Y et al. (2005). "Invasion of human tissue ex vivo by Borrelia burgdorferi". J Infect Dis 191 (10): 1747–1754. doi:10.1086/429632. PMID 15838803.
- Gruntar I, Malovrh T, Murgia R, Cinco M (2001). "Conversion of Borrelia garinii cystic forms to motile spirochetes in vivo". APMIS 109 (5): 383–388. doi:10.1034/j.1600-0463.2001.090507.x. PMID 11478686.
- Murgia R, Cinco M (2004). "Induction of cystic forms by different stress conditions in Borrelia burgdorferi". APMIS 112 (1): 57–62. doi:10.1111/j.1600-0463.2004.apm1120110.x. PMID 14961976.
- Escudero R, Halluska ML, Backenson PB, Coleman JL, Benach JL (1 May 1997). "Characterization of the physiological requirements for the bactericidal effects of a monoclonal antibody to OspB of Borrelia burgdorferi by confocal microscopy". Infect. Immun. 65 (5): 1908–15. PMC 175240. PMID 9125579.
- Brorson O, Brorson SH (1999). "An in vitro study of the susceptibility of mobile and cystic forms of Borrelia burgdorferi to metronidazole". APMIS 107 (6): 566–576. doi:10.1111/j.1699-0463.1999.tb01594.x. PMID 10379684.
- Brorson O, Brorson SH (2004). "An in vitro study of the susceptibility of mobile and cystic forms of Borrelia burgdorferi to tinidazole" (PDF). Int Microbiol 7 (2): 139–142. PMID 15248163.
- Brorson O, Brorson SH (2002). "An in vitro study of the susceptibility of mobile and cystic forms of Borrelia burgdorferi to hydroxychloroquine". Int Microbiol 5 (1): 25–31. doi:10.1007/s10123-002-0055-2. PMID 12102233.
- Liang FT; Yan J; Mbow ML et al. (2004). "Borrelia burgdorferi changes its surface antigenic expression in response to host immune responses". Infect Immun 72 (10): 5759–5767. doi:10.1128/IAI.72.10.5759-5767.2004. PMC 517580. PMID 15385475.
- Gilmore RD; Howison RR; Schmit VL et al. (2007). "Temporal expression analysis of the Borrelia burgdorferi paralogous gene family 54 genes BBA64, BBA65, and BBA66 during persistent infection in mice". Infect. Immun. 75 (6): 2753–2764. doi:10.1128/IAI.00037-07. PMC 1932849. PMID 17371862.
- Schutzer SE, Coyle PK, Reid P, Holland B (1999). "Borrelia burgdorferi-specific immune complexes in acute Lyme disease". JAMA 282 (20): 1942–1946. doi:10.1001/jama.282.20.1942. PMID 10580460.
- Newman K Jr and Johnson RC (September 1984). "T-cell-independent elimination of Borrelia turicatae". Infect Immun. 45 (3): 572–576. PMC 263332. PMID 6332075.
- Dattwyler RJ, Thomas JA, Benach JL, Golightly MG (Dec 1986). "Cellular immune response in Lyme disease: the response to mitogens, live Borrelia burgdorferi, NK cell function and lymphocyte subsets". Zentralbl Bakteriol Mikrobiol Hyg [A] 263 (1–2): 151–159. doi:10.1016/s0176-6724(86)80118-3.
- Kruger H, Pulz M, Martin R, Sticht-Groh V (Sep–Oct 1990). "Long-term persistence of specific T- and B-lymphocyte responses to Borrelia burgdorferi following untreated neuroborreliosis". Infection 18 (5): 263–267. doi:10.1007/BF01646998. PMID 2276818.
- Forsberg P, Ernerudh J, Ekerfelt C, Roberg M, Vrethem M, Bergstrom S (September 1995). "The outer surface proteins of Lyme disease Borrelia spirochetes stimulate T cells to secrete interferon-gamma (IFN-gamma): diagnostic and pathogenic implications". Clin Exp Immunol. 101 (3): 453–460. doi:10.1111/j.1365-2249.1995.tb03134.x. PMC 1553228. PMID 7664493.
- Yin Z, Braun J, Neure L, Wu P, Eggens U, Krause A, Kamradt T, Sieper J (January 1997). "T cell cytokine pattern in the joints of patients with Lyme arthritis and its regulation by cytokines and anticytokines". Arthritis Rheum. 40 (1): 69–79. doi:10.1002/art.1780400111. PMID 9008602.
- Jarefors S, Janefjord CK, Forsberg P, Jenmalm MC, Ekerfelt C (January 2007). "Decreased up-regulation of the interleukin-12Rbeta2-chain and interferon-gamma secretion and increased number of forkhead box P3-expressing cells in patients with a history of chronic Lyme borreliosis compared with asymptomatic Borrelia-exposed individuals". Clin Exp Immunol. 147 (1): 18–27. doi:10.1111/j.1365-2249.2006.03245.x. PMC 1810439. PMID 17177959.
- Olson CM, Hedrick MN, Izadi H, Bates TC, Olivera ER, Anguita J (2006-10-30). "p38 mitogen-activated protein kinase controls NF-kappaB transcriptional activation and tumor necrosis factor alpha production through RelA phosphorylation mediated by mitogen- and stress-activated protein kinase 1 in response to Borrelia burgdorferi antigens". Infect Immun. 75 (1): 270–277. doi:10.1128/IAI.01412-06. PMC 1828394. PMID 17074860.
- Ramesh G, Philipp MT (August 12–19, 2005). "Pathogenesis of Lyme neuroborreliosis: mitogen-activated protein kinases Erk1, Erk2, and p38 in the response of astrocytes to Borrelia burgdorferi lipoproteins". Neurosci Lett. 384 (1–2): 112–116. doi:10.1016/j.neulet.2005.04.069. PMID 15893422.
- Singh SK, Girschick HJ (2006). "Toll-like receptors in Borrelia burgdorferi-induced inflammation". Clin. Microbiol. Infect. 12 (8): 705–17. doi:10.1111/j.1469-0691.2006.01440.x. PMID 16842565.
- Marconi, RT; Earnhart, CG (2010). "Lyme Disease Vaccines". Borrelia: Molecular Biology, Host Interaction and Pathogenesis. Caister Academic Press. ISBN 978-1-904455-58-5.
- "Tick saliva." The Science Teacher 77.1 (2010): 14.
- "LymeVax". Product page. Pfizer. Retrieved 11 April 2012.
- Atlas of Borrelia (images of spirochetal, spheroplast and granular forms)
- NCBI Taxonomy Browser – Borrelia
- Borrelia burgdorferi B31 Genome Page
- Borrelia garinii PBi Genome Page
- Borrelia afzelli PKo Genome Page
- Schwan TG, Piesman J; Piesman (February 2002). "Vector interactions and molecular adaptations of lyme disease and relapsing fever spirochetes associated with transmission by ticks". Emerging Infect. Dis. 8 (2): 115–21. doi:10.3201/eid0802.010198. PMC 2732444. PMID 11897061.