Viral diseases in most cases unlike diseases caused by bacteria which are treated by using antibiotics are effectively dealt with only by the body's immune system. The reason for this being viruses cause diseases in a different manner as compared to bacterial infections; viruses are essentially parasitic in nature and require a host organism. They primarily invade bodily cells of the host organism and cause the cells to replace their normal functions with replication process of the virus.
A viral fever like influenza is often treated using anti viral drugs which primarily offer relief from the symptoms of the fever. Viral hemorrhagic fever which could in some cases be fatal is treated using the anti viral drug Ribavirin which works by interfering in the genetic replication process of the virus.
In case of a viral infection like influenza if the fever is mild it should be allowed to take its course while at the same time the patient should take rest along with high fluid intake, as a fever is primarily the body's indication that the immune system is eradicating the virus. However if the body temperature rises rapidly medicines like acetaminophen could be administered to relieve the effects of the fever.