Phylogeny of fever.

Vertebrates from fishes through mammals develop fevers in response to infection with various species of bacteria. In all vertebrates studied, these fevers were reduced by administering drugs known for their antipyretic properties in mammals. Based on the many similarities in the febrile response among the various vertebrate classes, it appears likely that fever is a primitive immunological response that has had a long phylogenetic history. The widespread occurrence of fever, an energetically expensive phenomenon, is further support for the hypothesis that fever is adaptive (beneficial to the infected host).