Assessing Schmallenberg Virus Disease in Sardinia (Italy) After the First Epidemic Episode in 2012

Schmallenberg virus (SBV), an Orthobunyavirus transmitted by Culicoides, causes congenital malformations and mild symptoms, such as fever, reduced appetite, decreased milk production, and occasional diarrhea, in ruminants. First detected in Central Europe in 2011, SBV spread across the continent, reaching Sardinia (Italy) in late 2012. This study evaluates the occurrence of SBV infections in Sardinian sheep from 2013 to 2024 by anatomo-pathological, virological, serological, and entomological data. The results suggest the presence of SBV infections in a continuous enzootic status over the years, without the cyclic waves observed in other countries, likely due to the unique sheep breeding management in Sardinia. Seroprevalence rates in the years 2022 and 2024 varied between 16.40% (C.I. = 12.28-20.52) and 21.53% (C.I. = 17.15-25.91) without significant differences between the two years analyzed. SBV was predominantly detected in C. imicola and C. newsteadi populations, while C. cataneii and C. sahariensis were identified as potential new vectors. Additionally, S- and M-segment sequences were obtained from two SBV isolates, S-sequences from a sample detected in 2020, and 21 archived cDNA samples from 2012. The S-segments showed high similarity among themselves and the reference strains, while the M sequences were significantly different, although potential artifacts from fetal samples must be considered. Overall, the results suggest widespread enzootic SBV circulation in Sardinia over the past decade, with a very low frequency of malformations in newly born sheep offspring.