The Collaborative International Dictionary of English v.0.48:

Spirochaeta \Spi`ro*chae"ta\, Spirochaete \Spi`ro*chae"te\, n.
   [L. spira a coil + Gr. ??? hair.] (Biol.)
   A genus of Spirobacteria similar to Spirillum, but
   distinguished by its motility. One species, the Spirochaete
   Obermeyeri, is supposed to be the cause of relapsing fever.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Relapsing \Re*laps"ing\, a.
   Marked by a relapse; falling back; tending to return to a
   former worse state.
   [1913 Webster]

   Relapsing fever (Med.), an acute, epidemic, contagious
      fever, which prevails also endemically in Ireland, Russia,
      and some other regions. It is marked by one or two
      remissions of the fever, by articular and muscular pains,
      and by the presence, during the paroxism of spiral
      bacterium (Spirochaete) in the blood. It is not usually
      fatal. Called also famine fever, and recurring fever.
      [1913 Webster]

WordNet (r) 3.0 (2006):

spirochaete
    n 1: parasitic or free-living bacteria; many pathogenic to
         humans and other animals [syn: spirochete, spirochaete]