paratenesis

[păr′ə-tə-nēsĭs]
n.
  1. The passage of a parasite by one or a series of hosts with no effect on the completion of the life cycle of the parasite.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.