Borrelia species x um, more irregular than treponemes 2. Can be stained in appropriate specimens (e.g. blood) using Giemsa 3. Number of axial filaments depends on species (e.g. 12 for B. recurrentis) 4. Microaerophlic, nutritionally fastidious but grow slowly in vitro 5. Either louse-borne (B. recurrentis) or tick-borne (e.g. B. hermsii, B. perkeri, B burgdorferi, etc.) 6. Currently 18 recognized species 7. Cause relapsing fevers or Lyme disease

Relapsing fever Borrelias 1. Possess a linear chromosome and plasmids (up to 14 plasmids per bacterial cell 2. Tick is the vector and injects bacteria into bloodstream after biting 3. Disseminated throughout the body 4. Causes high fever approx. 5-7 days post-infection, followed by subsidence and then subsequent relapse with fever. 5. Cycle may continue hence the name “relapsing fever”

Relapsing fever Borrelias (contd.) 6. Demonstrate antigenic variation #s Borrelia Serotype specific IgM Weeks post infection Sero Sero Sero 14. Anti 7 Anti21Anti14

Relapsing fever Borrelias (contd.) 7. Variation are in the variable major proteins (VMP) of the outer membrane. Two families of proteins - variable small amd variable large protein (Vsp and Vlp respectively) 8. Vsp (20kDa) and Vlp (36kDa) are lipoproteins anchored to the membrane via their lipids 9. VMPs may be involved in tissue tropism

10. Clearing in vivo occurs through complement-mediated lysis 11. The genes encoding the VMPs are located on plasmids and the chromosome. 12. A single bacterial cell can only express one antigenic type of VMP 13. How are genes activated to alter the antigenic profile of a bacterium?

Barbour & Restrepo (2000): Emerging Inf. Dis.6:451 p p p p p p p p + p p

VMP gene structure 1. The genes encoding the VMPS (vlp and vsp genes) share common properties facilitating recombinaion. 5’3’ ConstantVariableConstant 2. Upstream homology region is 50bp from 5’ region 3. Downstream homology site is 1kbp from 3’ end of gene

Borrelia direct repeat (Bdr) proteins 1. Bdr genes are found in all Borrelias 2. Sequence analysis indicates conserved functionaldomains 3. Precise function is unknown; signaling molecules??

Epidemiology of relapsing fever 1. Seasonal incidence in the US 2. Associated with campers, backpackers, etc. 3. Humans are incidental hosts for most relapsing fever Borrelias 4. Transmission by infected tick bite 5. B. recurrentis is a louse-borne disease of humans with interhuman transmission 6. Endemic in underdeveloped countries and associated with poverty and overcrowding

Lyme disease borreliosis 1. Caused by B. burdorferi 2. First recognized in 1977 among children in Lyme, Conn. believed to be suffering from rheumatoid arthritis 3. Begins as a localized skin infection but may spread as a second phase after latency involving multiple system (c.p. syphilis) 4. Reservoir of infection - Infected animals (deer & mice) Tick (Ixodes dammini) vector

Borrelia burdorferi 1. Long slender spirochetes (20-30 x microns) axial filaments 3. Possesses a linear chromosome as well as linear and circular plasmids 4. Does not demonstrate extensive antigenic variability 5. Linear plasmids encode two major outer surface lipoproteins, OspA and OspB.

B. burgdorferi Virulence 1. Initial adherence to host tissues In vitro B. burgdorferi bind to many cell types via integrins and glycosaminoglycans. 2. Multiple binding pathways or a single promiscuous pathway? 3. Observed binding specificities among different strains of B. burgdorferi may indicate differences in binding components

B. burgdorferi virulence contd. 4. Infection is frequently characterized by bacteria/ECM association. 5. Decorin is a host-cell, collagen-associated protein to which B. burgdorferi binds 6. Two bacterial porteins, DbpA and DbpB, mediate adherence to decorin

DbpA and B 1. Encoded by a large (approx. 54kbp) linear plasmids 2. Outer membrane proteins 3. Not homologous to other known adhesins 4. Following invasion into the connective tissue these proteins may play a role in establishment and spread of bacteria. 5. Have been considered as immunogens for vaccination. 6. Decorin regulates collagen fibril formation, inactivation of C1q, cell growth, etc. 7. Dbps could play a role in mediating inflammation

Interaction with finbrocytes 1. Fibrocytes express fibronectin and collagen, they target to connective tissue and recruit T cells. Therefore, they may play a role in mediating inflammation in connective tissue 2. B. burgdorferi bind, in vtiro, to finbrocytes 3. Bacteria reside deep within membrane invaginations without being phagocytosed 4. Location of binding may protect bacteria from immune system 5. Bacteria may coat themselves in host cell membrane (i.e. mimicry)

Epidemiology 1. One of the most common spirochetal diseases in US CDC, 2000

Epidemiology contd. 2. Seasonal incidence

Epidemiology contd. 3. Most cases are associated with the eastern seaboard states, upper midwest, and west 4. Most reliable clinical marker is the erythema migrans that occurs in 60-80% of infections 5. Cases confirmed by either isolation form clinical specimen OR demonstration of diagnostic levels of IgM and IgG 6. LYMErix is an rOspA-based vaccine