The Lyme disease spirochete has been found to take advantage of a tick protein in order to infect mice. The bacterium coats itself with a tick molecule that enables it to avoid host defences. If other vector-borne pathogens use this trick, it could provide a new target for therapeutics and vaccines. The Lyme disease agent, Borrelia burgdorferi, is maintained in a tick–mouse cycle1,2. Here we show that B. burgdorferi usurps a tick salivary protein, Salp15 (ref. 3), to facilitate the infection of mice. The level of salp15 expression was selectively enhanced by the presence of B. burgdorferi in Ixodes scapularis, first indicating that spirochaetes might use Salp15 during transmission. Salp15 was then shown to adhere to the spirochaete, both in vitro and in vivo, and specifically interacted with B. burgdorferi outer surface protein C. The binding of Salp15 protected B. burgdorferi from antibody-mediated killing in vitro and provided spirochaetes with a marked advantage when they were inoculated into naive mice or animals previously infected with B. burgdorferi. Moreover, RNA interference-mediated repression of salp15 in I. scapularis drastically reduced the capacity of tick-borne spirochaetes to infect mice. These results show the capacity of a pathogen to use a secreted arthropod protein to help it colonize the mammalian host.

The Lyme disease agent exploits a tick protein to infect the mammalian host