Effects of fever on host defense mechanisms after infection in the lizard Dipsosaurus dorsalis

Fever has never been proven beneficial in mammals, although it enhances survival in the lizard D. dorsalis infected with Aeromonas hydrophila. We examined the course of the infection and the function of host defence in febrile (41 degrees) and afebrile (35 degrees or 38 degrees) animals using this model. Infected, febrile lizards had sterile blood cultures, and 1-2 logs fewer bacteria in body tissues 6-12 h after infection. Granulocytes appeared early and in large numbers at the site of inoculation in febrile, but not afebrile, animals. We were unable to demonstrate effects of this small range of temperatures on in vitro growth rates of bacteria, on lizard granulocyte chemotactic or phagocytic functions, or upon serum antibody levels. Our results suggest that fever enhances some aspect of the early inflammatory response, leading to increased leucocyte emigration at the local site and containment of the infection.