ScienceDaily (Jan. 7, 2008) — Is host immunity enough to explain parasite success? Scientists based at the Universities of Glasgow, Scotland, and Lausanne, Switzerland, have shown that parasites balance host nutritive resources against immunity.

Pierre Bize, Caroline Jeanneret, Aurélie Klopfenstein, and Alexandre Roulin conducted research in Switzerland in a free-living colonial bird whose nestlings are heavily infested by blood sucking ectoparasites. They observed that ectoparasites achieved highest survival on nestlings in intermediate condition.

By manipulating nestling food resources and cutaneous immune responses, they then demonstrated that ectoparasite blood meal size, and in turn survival, is shaped positively by host nutritive resources and negatively by host immunity.

"The important point of our study," states Pierre Bize, the lead author, "is that although parasites have a poor survival when feeding on hosts in prime conditions, because these hosts can mount a potent immune response, the reverse is not true.

Indeed, parasites also have a reduced survival when feeding on hosts in poor conditions and with a low immune response, which points out that immunity is not the only factor accounting for parasite fitness." Alexandre Roulin adds, "The appraisal of what factors make a host profitable are vital for our understanding of host-parasite interactions, and in turn to the implement of well-designed parasite control programmes."

This research was published in the January issue of the American Naturalist.

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