Is fever adaptive?

Although there are clearly very many beneficial consequences of fever, there appear to be some persuasive arguments as to why the evolved febrile response could, in fact, be highly detrimental. Proponents of this argument will often reinforce that just because a mechanism has been evolutionarily conserved, it is not necessarily a good thing.

Harm to the Host

The increase in body temperature resulting from the raised thermoregulatory set point can be metabolically demanding on the host organism’s body, making it very energetically expensive to sustain a fever for a sufficiently long interval to actually help combat infection. Raised body temperatures can also result in dehydration, internal organ damage and lesions, cardiopulmonary strain, delirium, and pain in organisms experiencing fever, which are typically not considered to be healthy responses (18). Conflicting studies have also showed that in some cases, survival is not inhibited by administration of antipyretics such as aspirin. Opponents of fever as an adaptive mechanism would use these observations to argue that while fever is often tolerable for many host organisms, this does not mean that it must be either beneficial or essential.

Experimental Concerns

Other criticisms against the adaptive value of fever regard the manner in which many of the experiments on non-mammalian species have been performed. Studies on pathogens in vitro regarding their thermal tolerance might not be applicable to in vivo host-pathogen interactions, for example. It could also be argued that the results of many of the experiments performed on vertebrate ectotherms such as reptiles and amphibians might not hold true for humans, as our thermoregulatory processes are decidedly different. This could even possibly argued for experiments in mice, because although many mechanisms are conserved between mice and humans, there are also several differences in immune and physiologic responses.

 

An outdated adaptation?

Another argument against the adaptive benefit of fever in ectotherms, which thermoregulate behaviorally, is that the technique of aggregation to increase thermal mass can facilitate pathogen transfer between individuals. A study on tadpoles showed that they were more likely to contract fungal pathogen  Batrachochytrium dendrobatidis if they stayed close to other members of their species, a common behavioral trait of thermoregulating social amphibians (19). This suggests that behaviors such as febrile thermoregulation might have sufficiently high evolutionary inertia that they might cause problems for organisms exposed to novel pathogens for which instinct for a febrile response might keep its harmful effects while not effectively dealing with infection.