Regional hotspot for deadly horse disease found in Upper Austria

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The protected Crocidura leucodon, or bicolored white-toothed shrew, is a known bornavirus carrier. Photo: I, Dodoni CC-BY-SA-3.0 via Wikimedia Commons
The protected Crocidura leucodon, or the bicolored white-toothed shrew, is a known bornavirus carrier. Photo: I, Dodoni CC-BY-SA-3.0 via Wikimedia Commons

A regional hotspot for a virus that causes a deadly brain infection in horses has been identified in Upper Austria.

Bornaviruses cause a lethal form of encephalitis, called borna disease, in not only horses but also sheep, with only a handful of cases ever reported in Austria.

However, four horses from the same area of Upper Austria recently contracted the disease in a span of just two years. All cases occurred in winter.

Tests conducted on local bicolored white-toothed shrews, the only known reservoir host for the virus, confirmed suspicions of a local viral reservoir. But, for the first time, testing also uncovered the virus in a common shrew.

While the bornavirus is harmless in people, it targets the brain and the spinal cord in affected horses and sheep. Signs include behavioral disturbances and disorientation.

Occasional sporadic outbreaks of the disease have been documented in Central Europe, although case numbers have been in decline. Affected regions include eastern and southern Germany, the eastern part of Switzerland and the area bordering Liechtenstein, and the most western federal state of Austria, Vorarlberg.

Outbreak confirmed

Work by researchers from the University of Veterinary Medicine Vienna and the Austrian Agency for Health and Food Safety confirmed the outbreak of borna disease in a previously unaffected area of Austria.

The four horses who contracted the disease lived in locations no more than 17 kilometers apart.

The first indication of a possible borna disease outbreak came from two vigilant local veterinarians. They diagnosed a neurologic condition among four horses in Upper Austria and suspected that bornaviruses could be responsible. Examinations of the afflicted horses confirmed their suspicions.

“At the same time, we also tested the possible local carrier — shrews — to help assign a local aspect to the multiple cases of disease,” explained veterinarian Herbert Weissenböck, of the university’s Institute of Pathology and Forensic Veterinary Medicine.

More than 50% of the trapped bicolored white-toothed shrews were positively identified as carriers of the virus. But there also was an unexpected positive test for the common shrew − a species which had not, so far, been considered a possible carrier of the bornavirus.

“Further studies are needed to show whether this species also serves as a reservoir host or if this is an isolated case,” said Dr Norbert Nowotny, of the university’s Institute of Virology.

The researchers also compared the bornaviruses found in Upper Austria with the previously discovered Central European strains.

Nowotny said it would have been expected that the Upper Austrian bornaviruses would have been closely related to those in nearby Bavaria, but this was not the case. Instead, they were found to be closest to a viral strain from Rhineland-Palatinate, another German state.

He continued: “Since its description, this strain has been found in other areas in Germany and now also in Austria. This shows that we are still lacking important information about how the various strains of bornavirus spread.

A map depicting the geographical distribution of the Borna disease virus-1-positive horses and shrews. The inset shows the area in Upper Austria, which has been enlarged. Image: Weissenböck et al. doi:10.1038/emi.2017.36
A map depicting the geographical distribution of the Borna disease virus-1-positive horses and shrews. The inset shows the area in Upper Austria, which has been enlarged. Image: Weissenböck et al. doi:10.1038/emi.2017.36

“The identification of a previously unknown endemic area for bornaviruses in Upper Austria was a surprise for us all.”

The study team, reporting in the journal Emerging Microbes & Infections, said: “This study clearly demonstrates that the map of endemic areas for Borna disease virus-1 is far from complete and that new endemic pockets remote from the well-known affected regions may emerge from time to time.”

More on shrews

An earlier study by the team had confirmed that the protected bicolored white-toothed shrew represented a reservoir for bornaviruses. The viruses are present in high amounts in all organs of the shrews while the animals themselves remain asymptomatic.

“After an infection, the shrews remain lifelong hosts and even excrete the virus,” said Nowotny. With a protected species such as this, however, the question is how to best combat bornavirus infections.

The shrews must be kept out of the stables, for example through self-closing doors or barriers. Hygiene standards and regular controls also play an important role.

“This case has shown that many scientific studies begin with the watchful diagnosis by practicing veterinarians,” added Weissenböck.

“This awareness must be further strengthened. The good cooperation with the Austrian Agency for Health and Food Safety has shown that we can make rapid progress when we work together.

“The proof that the bornaviruses were present in both horses and shrews confirmed not only the veterinarians’ diagnosis but will also help us to develop strategies for the future.”

Infections of horses and shrews with Bornaviruses in Upper Austria: a novel endemic area of Borna disease
Herbert Weissenböck, Zoltán Bagó, Jolanta Kolodziejek, Barbara Hager, Günter Palmetzhofer, Ralf Dürrwald and Norbert Nowotny.
Emerging Microbes & Infections (2017) 6, e52; doi:10.1038/emi.2017.36

The study, published under a Creative Commons License, can be read here

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