Chronic fatigue syndrome is characterized by prolonged fatigue, muscular pain, and neurological problems  It is not known whether these symptoms are all caused by a single virus or whether each symptom is the result of a separate viral infection  A newly synthesized drug has been tested on those who suffer from chronic fatigue syndrome  Although the specific antiviral effects of this drug are unknown, it has lessened the severity of all of the symptoms of chronic fatigue syndrome
Thus there is evidence that chronic fatigue syndrome is, in fact, caused by one virus
Most syndromes that are characterized by related symptoms are each caused by a single viral infection.