My question was raised after receiving this information:

The primary reason the body raises its temperature (via the Hypothalamus in this case) is that bacteria and viruses tend to optimally thrive at 98.6F, which is also your body's optimal operating temperature.

I am just wondering if there are any viruses or bacteria that have gained the ability to prosper under fever temperatures through evolution? If not, why not? Is there any biological restriction stopping such viral evolution?


I will try to explain my question. As far as I know, evolution helps species to adapt to their environment. For example, when people started using antibiotics we got new bacteria resistant to those antibiotics.

If fever is part of the innate immune reaction to viruses and bacteria, why hasn't this resulted in selection for fever-resistant variants? Why has evolution apparently stopped in this case?

  • 1
    $\begingroup$ There are bacteria that live in hotsprings, for them 100c is comfortable. $\endgroup$
    – john-jones
    Commented Mar 16, 2013 at 7:11
  • 2
    $\begingroup$ Are you asking if there are pathogenic bacteria that thrive at higher body temperatures? $\endgroup$
    – blep
    Commented Mar 16, 2013 at 7:26
  • $\begingroup$ I have updated my question and tryied to explain it. $\endgroup$
    – ceth
    Commented Mar 16, 2013 at 7:42
  • $\begingroup$ Does anyone else cringe whenever stumbling upon 98.6°F? $\endgroup$ Commented Nov 13, 2014 at 16:44

1 Answer 1


Fever is just one of the many ways of the body's defense mechanism work. Under infection, human body can raise body temperature, release cytokins and activate white blood cells etc. Sometimes the bacteria can evade immune suppression or immune complement fixation so that they can stay inside a "fever-ish" body like they just don't care. Example: Pseudomonas aeruginosa. They can grow in 42 degree Celsius which surpass the normal fever temperature.

My answer may not be the best for your question. All I'm trying to say is that fever acts as a supportive role during an infection. Human body relies on heavy artilleries such as white blood cells and cytokin to clear the infection. That's why it will be more beneficial for the bacteria to evolve abilities to evade immune suppression and immune complement fixation. And bacteria know how to do those.


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