Mysteries solved: After 50 years of searching, researchers have finally discovered the cause of the deadly “staggering disease” in cats – a brain infection that primarily affects outdoor cats. This disease, which is associated with paralysis and cramps, is therefore caused by the so-called Rustrela virus – an RNA virus closely related to the rubella pathogen. Yellow-necked mice and wood mice were identified as reservoirs and carriers of the virus. If cats eat infected mice, they too can become infected.
Staggering disease in cats, also known as staggering disease or feline meningoencephalomyelitis, has only been known since the 1970s and is relatively rare. So far, the inflammation of the brain and spinal cord has mainly occurred in outdoor cats in Sweden, Austria and parts of Germany. Typical symptoms are spastic paralysis of the hind legs, tremors, cramps and behavioral changes in the animals. The disease often progresses so far within a few days or weeks that the cats have to be euthanized.
Who is the originator?
However, what causes this feline disease was unknown. “Although microscopic analyzes indicated a viral origin, the identity of the pathogen remained undiscovered for almost 50 years,” explain Kaspar Matiasek from the Ludwig Maximilians University in Munich and his colleagues. Due to the similarity of the neurological symptoms to Borna’s disease in horses, sheep and other even-toed ungulates, Borna disease virus 1 (BoDV) was suspected at times, but this was not confirmed.
In order to provide more clarity, Matiasek and his team have now once more examined the tissue and blood of 29 cats who died with the dizzy spell. The animals came from southern Sweden, Austria and Germany and were frozen or preserved in formalin for later analysis because the cause of the disease was unclear.
Rustrelavirus detected in diseased cats
In fact, the researchers found what they were looking for: “Using next-generation sequencing, we were able to find viral signatures in tissue samples from the diseased cats and then fully decode the viral genomes,” reports co-author Herbert Weissenböck from the University of Veterinary Medicine, Vienna. While the Borna virus might not be detected in any sample, the scientists found the RNA of the Rustrela virus (Rubivirus strelense, RusV) in 27 of the 29 affected cats.
This RNA virus is a relative of the human rubella virus and one of only two known rubiviruses. It was first discovered in 2020 following several animals died of encephalitis of unclear cause in a zoo near Stralsund. Since then, scientists have also detected the rustrelavirus in wild yellow-necked mice in this region.
The detection of the rustrela virus in the brain and nervous tissue of cats now proves that this viral pathogen is also responsible for the dizziness in cats. “Using special detection methods, we were able to show that the viruses multiplied in the nerve cells of the affected animals and thereby triggered the inflammatory reaction that caused the disease,” says Weissenböck. The cerebellum is one of the most frequently affected areas of the brain, which explains the movement disorders in infected cats.
Wood mice and yellow-necked mice as pathogen reservoirs
But how did the cats become infected? To clarify this, the research team also examined tissues from 116 rodents caught between 1995 and 2019 near the dizzy spell outbreaks in southern Sweden. The result: Unlike in Germany, the yellow-necked mice were not infected with the rustrela virus there, but some wood mice (Apodemus sylvaticus) were.
The scientists believe these results suggest that the two mouse species are the original reservoir hosts of rustrelavirus. Then, when outdoor cats catch and eat these mice, they too can contract the virus. However, Matiasek and his colleagues consider it unlikely that cats can infect each other with the rustrela virus. “The only sporadic occurrence of the disease, the lack of frequent outbreaks in multi-cat households and the restriction to outdoor cats support this,” say the researchers.
Exactly how the rustrela virus is transmitted, whether and how much of this pathogen an infected cat excretes and whether other animals form a reservoir still needs to be investigated. (Nature Communications, 2023; doi: 10.1038/s41467-023-36204-w)
Source: University of Veterinary Medicine, Vienna
