The present invention provides for isolated nucleic acid sequences encoding viruses; isolated polypeptides comprising amino acid sequences of the virus; vectors comprising the viral nucleic acid sequences; cells comprising the vectors; antibodies and antigen binding fragments thereof which have binding specificity for the virus; methods of detecting or screening for the virus (e.g., in an individual); methods of identifying agents that inhibit the virus; methods of inducing an immune response to the virus; methods of treating disease associated with the presence of XMRV in an individual (e.g., cancer such as prostate cancer); methods of detecting asymptomatic cancer (e.g., prostate cancer); methods of identifying an individual at risk for developing cancer (e.g., prostate cancer); and kits for detecting the virus.