An Emerging Viral Infection in Horses in Central Europe: Suspected Shamonda Virus Seroconversion in Asymptomatic Horses in Baden-Württemberg from June to September 2026

The first detection of the Shamonda virus in Central Europe occurred in mid-June 2026. Direct detection of the virus in blood or cerebrospinal fluid from living horses has not yet been reliably achieved. Serological examinations could therefore be crucial for future diagnostics. This study aimed to determine whether clinically healthy horses develop antibodies against viruses of the simbu serogroup and at what point the first positive antibody titers can be detected. To this end, blood sera from eleven clinically healthy horses based in southern Germany were examined retrospectively at three different time points between June and September 2026. Serological testing was performed using the ID Screen® Schmallenberg virus Multi-species ELISA kit; Innovative Diagnostics, Grabels, France. The results showed that all horses were seronegative or doubtful (one horse) in June (time point 1) and seronegative in July 2026 (time point 2). All eleven horses tested positive for antibodies in August or September (time point 3). There was a significant increase in antibody titers between time point 1 and time point 3, as well as between time point 2 and time point 3. The study found that even clinically healthy horses had been exposed to the pathogen and developed antibodies. Therefore, a positive antibody titer is not necessarily associated with clinical disease.