Science doi:10.1126/science.1179052 (2009)

Researchers have linked chronic fatigue syndrome, a debilitating disease of unknown cause, to an infectious retrovirus that has also been associated with prostate tumours.

Judy Mikovits at the Whittemore Peterson Institute in Reno, Nevada, and her colleagues found that 67% of 101 patients diagnosed with chronic fatigue syndrome carried the retrovirus XMRV in their blood, whereas fewer than 4% of 218 healthy individuals did.

The virus was able to spread from infected immune cells to cultured prostate cancer cells. The genomes of the XMRV strains associated with prostate cancer are more than 99% identical to those correlated with chronic fatigue syndrome, which is marked by increased cancer susceptibility. The authors say further study is needed to determine whether the virus causes the syndrome and if it is responsible for the elevated cancer risk.