General Characteristics of Borrelia
Basic features of Borrelia species
- Gram-negative, corkscrew-shaped spirochetes
- Larger than Treponema species
- Visualization:
- Dark-field microscopy
- Wright or Giemsa stain
- Difficult to visualize using Gram stain
- Microaerophilic
- Surrounded by an additional phospholipid-rich outer membrane and few exposed proteins
- Difficult to culture on ordinary media; Barbour-Stoenner-Kelly (BSK) medium is commonly used.
Dark-field microscopy of Borrelia burgdorferi
Image: “Borrelia burgdorferi (CDC-PHIL-6631) lores” by CDC. License: Public DomainClinically relevant species
- Lyme disease:
- B. burgdorferi
- B. afzelii
- B. garinii
- Relapsing fever:
- Tick-borne disease is associated with multiple species and includes:
- B. hermsii
- B. turicatae
- B. miyamotoi
- B. hispanica
- B. duttoni
- B. persica
- Louse-borne: B. recurrentis
- Tick-borne disease is associated with multiple species and includes:
Pathogenesis
Reservoirs
- Rodents
- Birds
- Bats
- White-tailed deer
- Humans (B. recurrentis)
Transmission
- Ticks
- Occurs through saliva injection during feeding
- Ticks are usually very small and the bite is often unnoticed.
- Longer attachment is associated with a higher risk of transmission.
- Associated species
- Ixodes scapularis (deer tick)
- Ornithodoros
- Louse
- Species: Pediculus humanus corporis (human body louse)
- Lives on clothing
- Only feeds on humans
- B. recurrentis is introduced when the louse is crushed by humans.
- Can enter through breaks in the skin or conjunctivae (from rubbing eyes)
- Not transmitted from louse saliva or feces
- Species: Pediculus humanus corporis (human body louse)
Virulence
- Motility
- Possess numerous axial filaments
- Thin endoflagella in the periplasmic space
- Allows them to move in a spinning fashion
- Propels the organism through blood and extracellular matrix
- Allows escape from phagocytosis
- Possess numerous axial filaments
- Outer surface proteins (Osps)
- Surface lipoproteins can be up- or down-regulated to facilitate transmission.
- OspA
- Responsible for attachment to the midgut of ticks
- Down-regulation results in detachment and transfer to the saliva of ticks.
- OspC
- Allows invasion through the host skin
- Important for the use of plasminogen
- Digests fibrin and glycoproteins
- Assists movement through extracellular matrix
- Variable major proteins (VMPs) provide antigenic variation.
- Borrelia are able to change major antigens on their surface.
- Allows the bacteria to evade the adaptive immune response of the host
- Endo- and exotoxins are generally not produced; symptoms are due to the immune system of the host.
Axial filaments of Borrelia:
Axial filaments are made up of multiple periplasmic flagella (bottom picture). This allows the spirochete (top picture) to move in a spinning fashion.
At-risk populations
- Tick-borne diseases:
- Hikers
- Campers
- Woodworkers
- Louse-borne diseases:
- Refugees
- Homeless
Diseases Caused by Borrelia
The following diseases are caused by Borrelia:
| Disease | Lyme disease | Relapsing fever |
|---|---|---|
| Associated species |
|
|
| Clinical manifestations |
|
|
| Complications |
|
|
| Diagnosis | Clinical, supported using ELISA and Western blot | Clinical, dark-field microscopy, Giemsa stain, or Wright stain of blood smear |
| Management |
|
|
| Prevention |
|
|
TBRF: tick-borne relapsing fever
LBRF: louse-borne relapsing fever
AV: atrioventricular
ARDS: acute respiratory distress syndrome
ELISA: enzyme-linked immunosorbent assay
PEP: post-exposure prophylaxis
Comparison of Spirochetes
Spirochetes are gram negative, spiral shaped, and motile. The following table briefly compares some clinically relevant spirochetes:
| Organism | Treponema pallidum pallidum | Other T. pallidum subspecies | Treponema carateum | Borrelia burgdorfi | Borrelia recurrentis | Leptospira interrogans |
|---|---|---|---|---|---|---|
| Micro |
|
|
|
|
|
|
| Virulence |
|
|
|
| Antigenic variation |
|
| Reservoir | Humans | Humans | Humans |
| Humans |
|
| Transmission | Sexual contact | P2P contact | P2P contact | Ixodes tick | Louse | Direct contact with animal tissue or fluids |
| Clinical | Syphilis |
| Pinta | Lyme disease | Relapsing fever |
|
| Diagnosis |
|
|
|
| Blood-smear analysis |
|
| Management |
|
|
|
|
|
|
Osp: outer surface protein
LPS: lipopolysaccharide
P2P: person-to-person
Microaero: microaerophilic
VDRL: Venereal Disease Research Laboratory test
FTA-ABS: fluorescent treponemal antibody absorption
ELISA: enzyme-linked immunosorbent assay
PCR: polymerase chain reaction
Visual comparison of spirochetes on electron micrograph: thick spirals of Treponema
Image: “Treponema pallidum” by Dr. David Cox. License: Public Domain
Visual comparison of spirochetes on electron micrograph: Borrelia, which are larger than Treponema
Image: “Lyme disease parasite, Borrelia burgdorferi” by Claudia Molins. License: Public Domain
Visual comparison of spirochetes on electron micrograph: hooked ends of Leptospira
Image: “A filtration-based technique for simultaneous SEM and TEM sample preparation for the rapid detection of pathogens” by Beniac DR, Siemens CG, Wright CJ, Booth TF. License: CC BY 3.0, edited by Lecturio.
References
- Barbour, A.G. (2020). Clinical features, diagnosis, and management of relapsing fever. In Mitty, J. (Ed.), Uptodate. Retrieved December 21, 2020, from https://www.uptodate.com/contents/clinical-features-diagnosis-and-management-of-relapsing-fever
- Barbour, A.G.(2020). Microbiology, pathogenesis, and epidemiology of relapsing fever. In Mitty, J. (Ed.), Uptodate. Retrieved December 22, 2020, from https://www.uptodate.com/contents/microbiology-pathogenesis-and-epidemiology-of-relapsing-fever
- Barbour, A.G. (2020). Microbiology of Lyme disease. In Mitty, J. (Ed.), Uptodate. Retrieved December 22, 2020, from https://www.uptodate.com/contents/microbiology-of-lyme-disease
- Gladwin, M., & Trattler, B. (2008). Clinical microbiology made ridiculously simple (4th edition). Miami: MedMaster
