[Frontiers in Bioscience 14, 3051-3063, January 1, 2009]

Molecular characterization of the tick-Borrelia interface

Aravinda Manu de Silva1, Katharine Rose Tyson1, Utpal Pal2

1Department of Microbiology and Immunology University of North Carolina School of Medicine, Chapel Hill, NC 27599, 2Department of Veterinary Medicine, University of Maryland, College Park, MD 20742-3711

TABLE OF CONTENTS

1. Abstract
2. Introduction
3. The Lyme disease Borrelia
3.1. Genome of B. burgdorferi
3.2. B. burgdorferi distribution within vector
3.3. Regulation of B. burgdorferi gene expression at the vector-host interface
3.4. B. burgdorferi antigenic variation within ticks
3.5. B. burgdorferi genes of functional significance in the vector
3.5.1. B. burgdorferi ospAB operon
3.5.2. B. burgdorferi ospC
3.5.3. B. burgdorferi genes on lp25 required for tick infection
3.5.4. B. burgdorferi chromosomal genes required in the vector
3.6. Tick proteins that facilitate B. burgdorferi transmission
3.6.1. Salp15- a tick protein that binds to OspC
3.6.2. The tick receptor for OspA (TROSPA)
3.6.3. The Isac family of proteins
3.7. Tick immune system and B. burgdorferi
4. Tick-borne relapsing fever Borrelia
4.1. Relapsing Fever Borrelia and tick interactions
5. Tick-transmission blocking vaccines
6. Summary, outstanding questions and future directions
7. Acknowledgements
8. References

1. ABSTRACT

Spirochetes in the genus Borrelia are responsible for tick-borne relapsing fever and Lyme disease. Borrelia-tick interactions are highly specific as each species of Borrelia is only transmitted by one or a few closely related species of ticks. Borrelia colonize the gut or salivary glands of ticks. Several Borrelia genes required for tick colonization or transmission have been identified. Borrelia genes required for transmission are induced by a pathway controlled by the alternate sigma factors RpoN (54) and RpoS (S). A protein in the gut of I. scapularis ticks that functions as a receptor for B. burgdorferi has been identified. In addition, Ixodes tick saliva has proteins that alter host hemostasis and immunity, and some of these salivary proteins directly interact with Borrelia to facilitate transmission and host infection, whereas others appear to assist Borrelia indirectly by suppressing host defense mechanisms. The exciting discoveries on Borrelia-tick interactions are also being translated into novel preventive measures such as transmission blocking vaccines.