ABSTRACT
Adaptations are usually regarded as the material products of natural selection acting on differential reproductive success. For a parasite, reproductive success depends not only on its survival and multiplication within a given host, but also on its ensuring transmission to a new host. Adaptations relating to transmission and niche selection within the host are discussed using Giardia Iamblia and Trypanosoma brucei as examples of an intestinal parasite transmitted by cysts through the faeco-oral route and a blood parasite transmitted by vector, respectively.
