Any infection caused by a virus.
Symptoms of viral infection vary, but typically include fever, generalized aches, chills, fatigue, and symptoms that are specific for that virus. For example, the cold virus usually produces mucus in the nose and throat, the mononucleosis virus produces severe fatigue and, sometimes, liver enlargement, and the polio virus produces paralysis. Symptoms can be chronic or short-lived, depending on the type of virus, as well as the individual's level of immune function. In some cases, such as HIV, viral infections can be life-threatening.
Types: There are many different types (literally hundreds) of infectious viruses, such as cold and flu viruses, herpes viruses, HIV, etc. Proper treatment lies in determining which type of virus is affecting the system so that it can be effectively dealt with.
Viruses are naturally occurring microorganisms. They are most commonly spread through respiratory routes and bodily fluids, such as blood and semen. Once they gain a foothold in the body, viruses seek to replicate themselves and then spread to others. Sneezing, touching, and eating infected foods are some of the more common ways in which viruses travel from one person to another.
Note: Viral infections do not respond to antibiotics.