Answer: Fever ( also termed as pyrexia) is a state of body in which internal body temperature rises substantially beyond the normal range of body temperature. It is commonly caused by the infection of pathogenic agents ( such as virus and bacteria) in the body.
It is a common way to fight against and eliminate the infection as it enhances the amount of anticancer and antiviral interferon in the blood, which do not allow the infectious agents to replicate. Apart from this, they are also temperature sensitive and therefore replication becomes difficult.
Thus, presence of a fever usually corresponds to stimulation of immune response of body to fight against the infectious agents.