Retroviruses and Chronic Fatigue Syndrome Retroviruses are one of the biggest insults to immunity and a potential cause involved in Chronic Fatigue Syndrome.[1] A retrovirus is a virus whose genes are encoded in RNA, and, using an enzyme called reverse transcriptase, replicates itself by first reverse-coding its genes into the DNA of the cells it infects.[2] Once it’s in the DNA, it’s there for good. Every time your DNA replicates so does the retrovirus. It has been estimated that approximately 8-15% of our genome is compromised of retroviruses, and some controversial data shows they are potentially oncogenic.