Magouras et al.
Neurological disease suspected to be caused by tick-borne encephalitis virus infection in 6 horses in Switzerland
J Vet Intern Med. 2022;36(6):2254-2262

In horses, TBE virus infection is mostly asymptomatic or takes a subclinical course and does not cause severe illness. However, TBE has been described in horses with signs like ataxia, seizures, and paralysis of the neck and shoulder muscles.

A retrospective study has been conducted in Switzerland from 2011 to 2020, and a total of 74 horses presented with neurologic diseases at an equine hospital were analyzed in detail for various flavivirus infections (e.g., Usutu, West Nile virus and TBE virus).

Sera from nine horses were tested positive in a TBE neutralizing assay. Six of these nine sera were analyzed for TBE IgM antibodies, and TBE virus infection was confirmed in five cases. The six horses lived in TBE endemic areas of Switzerland.

Although no validated treatment of TBE virus infection in horses is available, five of the six horses were treated with nonsteroidal anti-inflammatory drugs, corticosteroids, dimethylsulfoxide, antimicrobials, valacyclovir and vitamin E. Three horses fully recovered after three to four months, two horses still showed residual signs of ataxia after 12 months, and one of the six horses died.

This study indicates that TBE virus infection in horses can exhibit signs of neurologic disease. Therefore, awareness among horse owners and veterinarians should be raised, especially in TBE-endemic areas.

Furthermore, the establishment of harmonized laboratory diagnostic criteria would help to address the issue of diagnostic cross-reactions.

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