A serious neurological disease affecting cats may be caused by a relative of the rubella virus called rustrela virus, a new paper claims.

It is important to note that the paper, published on the preprint server bioRxiv, has not yet been peer-reviewed.

Staggering disease was first recorded in the 1970s in the Lake Mälaren region of Sweden. Symptoms include cats losing control of their hind legs, inability to retract claws, tremors, and seizures. It usually progresses over a few weeks and has no cure, with affected animals usually being euthanized for welfare reasons.

Previous studies have pointed to Borna disease virus as the cause, but the authors of the new study write that “results suggesting natural BoDV-1 [Borna disease virus 1] infections in cats with 'staggering disease' in Sweden remained inconclusive and were later refuted on the grounds of new standards.”

Researchers analyzed 29 brains of cats observed to have staggering disease-like symptoms: 15 from Sweden, 9 from Austria, and 5 from Germany. The brains were either frozen or formalin-fixed paraffin-embedded.

No Borna disease virus RNA or antigens were detected in the samples. However, when they looked for rustrela virus (RusV), it was another story.

“We report the detection of RusV RNA and antigen […] in brain tissues of 28 out of 29 cats,” the authors write.

The discovery of rustrela virus was published in the journal Nature in 2020. It had killed a tree kangaroo, a capybara, and a donkey at a zoo in Germany, and was also found in yellow-necked field mice in and around the zoo. The authors of the new study point to wood mice as a reservoir for rustrela virus, and thus for staggering disease.

[H/T: New Scientist]