A Novel Pathogen of an Emerging Infectious Disease (Large Kidney Disease) in Farmed Blue Foxes

An emerging infectious disease (EID) in foxes called "large kidney disease", characterized by enlarged kidneys, has been breaking out in fox farms in China, although its pathogenesis has not yet been elucidated. Here, we performed viral metagenomics sequencing on diseased fox tissue samples that identified a virus with 82.6% homology to the xenotropic murine leukemia virus-related virus (XMRV) PreXMRV-1 provirus strain (GenBank accession number NC_007815.2) in sick fox tissue. It was named PreXMRV-20, and its genome was verified by reverse transcription-polymerase chain reaction (PCR) and PCR product sequencing. Nonenveloped and polygonal virus-like particles consistent with the shape and size of XMRV were observed by negative staining electron microscopy. Administered subcutaneously, PreXMRV-20 infected weaned foxes, leading to growth retardation. The discovery of the PreXMRV-20 strain (the first isolation of an XMRV homolog in blue foxes) identifies a potential public health issue in blue fox breeding since XMRV has been confirmed to be a zoonotic virus.