How Rising Body Temperatures in Animals Offer Insights for Human Fever Response

Fever is a common biological response observed across a wide range of creatures, from humans to insects, and even reptiles and fish. While many believe that pathogens like viruses directly cause fevers, the reality is more complex: our bodies elevate internal temperature as a strategic immune response. When the immune system detects harmful microbes, it releases substances called pyrogens, which signal the hypothalamus in the brain to raise the body's temperature set point. This process results in fever, typically increasing body temperature to 100.4–104°F (38–40°C), and plays a vital role in combating infections by creating an environment hostile to invading microbes.

Animals, including mammals, reptiles like lizards, fish, and insects, actively use fever as a defense mechanism. For instance, dogs exhibit lethargy, loss of appetite, and shivering when they have a fever, similar to humans. Lizards tend to migrate to warmer areas when ill, while zebrafish increase their body temperature during infection, which enhances their immune response and survival chances. Naked mole rats, despite their unusual physiology, also generate fevers in response to infection. Insects like desert locusts and social insects such as honeybees exhibit behavioral thermoregulation, raising hive temperatures to suppress pathogen growth—for example, honeybees increase hive temperature to prevent fungal spores from germinating.

Understanding these natural responses emphasizes that raising body temperature is a protective evolutionary trait. However, in humans, the instinct often is to lower fevers—using medications like aspirin or applying cold. While high fever (above 103°F or 39.4°C) warrants medical attention, mild to moderate fevers can actually aid recovery by enhancing immune efficiency. Historically, some treatments, such as the early 20th-century malariotherapy, deliberately induced high fevers to treat bacterial infections, demonstrating the therapeutic potential of fever.

Fever's evolutionary roots are evident in the convergent development of this trait across diverse species, suggesting it's a highly effective adaptation. Despite different evolutionary paths, these organisms share the challenge of infection and have arrived at the same solution: fever. Ongoing research aims to better understand its role in immune response and how it can be harnessed to improve health outcomes.

Source: https://medicalxpress.com/news/2025-05-animals-germs-mother-nature-humans.html