Mystery of fatal ‘Staggering disease’ unravelled: Novel rustrela virus causes severe encephalomyelitis in domestic cats

‘Staggering disease’ is a neurological disorder considered a threat to European domestic cats ( Felis catus ) for almost five decades. However, its aetiology has remained obscure. Rustrela virus (RusV), a relative of rubella virus, has recently been shown to be associated with encephalitis in a broad range of mammalian hosts. Here, we report the detection of RusV RNA and antigen by metagenomic sequencing, RT-qPCR, in-situ hybridization and immunohistochemistry in brain tissues of 28 out of 29 cats with non-suppurative meningoencephalomyelitis and ‘staggering disease’-like neurological disorder from Sweden, Austria, and Germany, but not in non-affected control cats. Screening of possible reservoir hosts in Sweden revealed RusV infection in wood mice ( Apodemus sylvaticus ). Our work strongly indicates RusV as the long-sought cause of feline ‘staggering disease’. Given its broad host spectrum and considerable geographic range, RusV may be the aetiological agent of neuropathologies in further mammals, possibly even including humans. ### Competing Interest Statement The authors have declared no competing interest.