When people get sick, they often develop a fever. What is the effect of an increased body temperature on viruses and bacteria in the body? Is it beneficial to the infected body? Importantly, often fever-reducing agents like aspirin are prescribed when people are sick. Doesn't this counteract any benefits of fever?
Fever is a trait observed in warm and cold-blooded vertebrates that has been conserved for hundreds of millions of years (Evans, 2015).
Elevated body temperature stimulates the body's immune response against infectious viruses and bacteria. It also makes the body less favorable as a host for replicating viruses and bacteria, which are temperature sensitive (Source: Sci Am).
The innate system is stimulated by increasing the recruitment, activation and bacteriolytic activity of neutrophils. Likewise, natural killer cells' cytotoxic activity is enhanced and their recruitment is increased, including that to tumors. Macrophages and dendritic cells increase their activity in clearing up the mess associated with infection.
In fact, taking pain killers that reduce fever have been shown to lead to poorer clearance of pathogens from the body (Evans, 2015). In adults, when body temperature reaches 104 oF (40 oC) it can become dangerous and fever reducing agents like aspirin are recommended (source: eMedicine)
- Evans, Nat Rev Immunol (2015); 15(6): 335–49
Fever normally under hypothalamic heat center's control which stays at limbic system of brain . Hypothalamus sets its own set point 36.4-37.2 in healthy peoples by some molecules named exogenous and endogenous pyrogens, especially PGE2 ,TNF and IL1.
The most important mechanism for fever is directing blood flow from skin to deep vascular pools and preventing heat loss from skin. Thats also cause to cold distal parts of our extremities.
When pathogen microorganisms and their toxins invade our blood, our immune response is being activated. Inflammation process starts which have four components: "Tumor ,Rubor ,Calor ,Dolor". So we experience swelling, redness, fever and pain in other words. Our white blood cells emits prostaglandin and leukotrienes that activating inflammation and those cells to migrate there.
After interact between our defence and microbes, these pyrogens activates hypothalamus heat center. Then temperature set point rises. That activates vasomotor and cortical response. With vasomotor activation, blood flow is directed to deep blood pools and the other side smooth muscles spontaneously contracting generate extra heat. With activation cortical pathways patient feels needing to increase heat or prevent heat loss by e.g wearing more clothes, getting in bed, changing posture to decrease heat losing total area...
So what are all these mechanisms for? Our body resistance increases. Also metabolism speed rises to fight with pathogen. Microorganisms and many toxins have protein components , heat helps denaturation of those proteins and being inactivated. But also our basis contains proteins. So too high temperature is dangerous for our body. When we take analgesics which also decrease fever, thats the purpose to control fever in acceptable intervals. (source:Pubmed) for more read