Researchers have discovered a link between chronic fatigue syndrome (CFS) and a virus. The virus, known as XMRV, has previously been linked with prostate cancer.

Specifically, the XMRV was detected in the blood of 68 out of 101 (67%) subjects with CFS, compared with 8 out of 218 (3.7%) healthy control subjects. The study’s authors point out that this link does not necessarily mean that XMRV causes CFS. Alternatively, people with CFS may be at a higher risk of contracting XMRV, due to a depressed immune response.