Temperature Fluctuations Impact Animal Immune Systems and Disease Resistance

Temperature directly affects the immune systems of vertebrate animals, regardless of how they regulate their body heat. Research indicates that a slight increase in temperature can initially boost an animal's immune response. However, temperatures exceeding an optimal range can favor disease-causing pathogens.

This presents a challenge as climate change is expected to expand the geographical range of many pathogens. Understanding the relationship between temperature and animal immune systems offers new strategies for species protection. One example involves using "frog saunas" to help amphibians combat chytrid fungus.

Animals maintain body temperature in different ways. Mammals and birds are endotherms, generating internal heat to keep their body temperature stable. Poikilotherms, such as snakes and lizards, rely on external sources to regulate their temperature. Both strategies aim to keep body temperature near an optimal level.

Pathogens also have temperature preferences. Some thrive in warmer conditions, while others prefer cooler environments. For instance, the Ebola virus replicates best at 41 degrees Celsius, while the rhinoviruses causing the common cold prefer cooler temperatures around 33 degrees Celsius. The fungus responsible for white-nose syndrome in bats thrives in cold temperatures, typically between 12 and 16 degrees Celsius.

When an animal's body temperature falls below its optimal range, its specific immune defenses can weaken. This impairment primarily affects specific immune responses, leaving innate immune mechanisms largely intact. For example, during hibernation, ground squirrels experience reduced specific immune defenses due to lower body temperatures.

Conversely, heat can induce a fever in endotherms, raising body temperature to inhibit pathogen replication and trigger specific immune responses. Poikilotherms use behavioral fever, moving to warmer areas to enhance their immune response when infected. Extreme heat, however, can stress or kill an animal.