In August 2024, Switzerland reported its first confirmed cases of bluetongue disease (BT) caused by the newly emerging serotype 3 of the bluetongue virus (BTV-3). Concurrently, cases attributed to the previously circulating serotype 8 (BTV-8) continued to occur. Between August 2024 and February 2025, BTV-3 infections were detected in 2,435 livestock holdings across the country, while BTV-8 was identified in 234 holdings. Of the total 2,669 affected premises, the majority (69%) were cattle farms, followed by sheep farms (30%) and 20 goat holdings (1%).
Bluetongue is a viral disease affecting ruminants and is transmitted by Culicoides biting midges. Clinical symptoms are predominantly observed in sheep and cattle. Sheep frequently exhibit severe symptoms such as pyrexia, mucosal inflammation, lameness, and abortions. In contrast, clinical symptoms in cattle are often milder but may lead to substantial reductions in productivity, including decreased milk yield, increased somatic cell counts, elevated non-return rates, as well as abortions and neonatal symptoms in calves.
Currently, calves born to cows infected during the autumn 2024 outbreak are being delivered. As of March 2025, there has been a significant increase in the proportion of bluetongue-positive calves, accounting for approximately 40% of all new cases (half of which involve calves less than five days old). Field experience and diagnostic observations indicate that such calves may be born both antigen- and antibody-positive and multiple calves have already been presented with confirmed hydranencephaly at the Vetsuisse Faculty. In various other viral diseases (BVD virus, Schmallenberg virus, and Akabane virus) [1], as well as during the BTV-8 outbreak in the Netherlands in 2008 [2], congenital defects affecting the brain have been described.
