Pre-existing bacterial infections, not stress fever, influenced previous studies which labeled Gerrhosaurusmajor an afebrile lizard species

Abstract

Early studies indicated that the Sudan plated lizard, Gerrhosaurus major, did not exhibit a febrile response when challenged with bacterial pyrogen. More recent results indicated that a 14-day antibiotic treatment regime produced a significant decrease (0.5±0.1°C) in the mean selected body temperature (MSBT) for this species (31.3±0.2–30.8±0.2°C). The antibiotic treatment results suggested that G. major already had a fever caused by a pre-existing bacterial infection. The current study was designed first to determine if a sub-population of G. major, with a higher mean pre-antibiotic treatment MSBT would exhibit a greater decrease in MSBT after antibiotic treatment. A 14-day antibiotic treatment regime for G. major ( N=7) with MSBTs≥31.9°C (mean 32.4±0.2°C) produced a significant decrease of 1.7±0.4°C in MSBT to 30.7±0.3°C. Analysis of the combined antibiotic treatment MSBT data from [13] and the current study demonstrated that the magnitude of the change in MSBT after antibiotic treatment was dependent upon the pre-antibiotic treatment MSBT. These data imply that animals with a greater pre-treatment MSBT and greater MSBT change had a greater magnitude fever. In the second portion of this study the MSBT for individual lizards was measured during separate experiments using both indwelling cloacal thermocouples taped to the tail of the lizard and telemeters implanted into the peritoneal cavity of the lizard. This second study was designed to determine if measurement of T b using thermocouples induced a stress fever which may have masked a portion of the pyrogen-induced fever. The MSBT measured using indwelling cloacal thermocouples (30.5±0.3°C) was not significantly greater ( P>0.05) than the MSBT measured using telemeters (31.0±0.2°C). The results of the experiments from this study demonstrate that the previously reported afebrile state for G. major was the result of animals having pre-existing bacterial infections. G. major does exhibit a febrile response similar to other lizard species.