Febrile response to infection in the American alligator ( Alligator mississippiensis)

Abstract

Temperature probes were inserted into the stomachs of juvenile American alligators ( Alligator mississippiensis) maintained outdoors at ambient fluctuating temperatures. Internal body temperatures ( T b) were measured every 15 min for two days, and then the alligators were injected with bacterial lipopolysaccharide (LPS), pyrogen-free saline, or left untreated. Alligators injected intraperitoneally with LPS exhibited maximum T bs 2.6 ± 1.1 °C and 3.5 ± 1.2 °C higher than untreated control animals on days one and two after treatment, respectively. T bs for these animals fell to within control ranges by day three postinjection. Similarly, mean preferred body temperatures (MPBTs) were significantly higher for LPS-injected alligators on days one (4.2 ± 1.8 °C) and two (3.5 ± 1.6 °C) after treatment. Intraperitoneal injection of heat-killed Aeromonas hydrophila, a gram-negative bacterium known to infect crocodilians, resulted in a fever while injection of Staphylococcus aureus (gram positive) did not elicit a febrile response. Injection of LPS in alligators maintained indoors in a constant temperature environment resulted in no increase in internal T b. These results indicate that alligators did not exhibit a febrile response in the absence of a thermal gradient, and suggest that febrile responses observed are probably behavioral in nature.