Serological Evidence of Schmallenberg Virus Exposure in Ruminant Abortion Cases from Selected Regions of Iran: A Virus Neutralization Test‐Based Study

Background Schmallenberg virus (SBV), an emerging Orthobunyavirus, is associated with reproductive disorders in ruminants. Although SBV has spread from Europe into parts of Asia, epidemiological data from Iran remain limited. Objective To investigate SBV exposure among ruminants from selected regions of Iran using the virus neutralization test (VNT). Methods Serum samples from 92 ruminants (37 sheep and 55 cattle) with a history of abortion or SBV‐compatible clinical signs were collected from three provinces in eastern (Sistan and Baluchestan), central (Qazvin), and western (East Azerbaijan) Iran. Sera were inactivated, serially diluted (1:5–1:640), and tested in quadruplicate by VNT on BHK‐21 cells with a back‐titrated SBV inoculum (125 TCID 50 /well). Results Seventy of 92 samples (76.1%) were positive for SBV‐neutralizing antibodies (≥1:10). Seropositivity was 87.5% (14/16), 64.1% (25/39), and 83.8% (31/37) in the eastern, central, and western regions, respectively. Mean VN 50 titres varied descriptively, with the highest mean titre observed in the western region (60.47 ± 57.65), followed by the central (43.30 ± 56.65) and eastern (22.73 ± 13.72) regions. Although the Kruskal–Wallis test indicated an overall difference in antibody titres ( p = 0.022), post hoc pairwise comparisons with Bonferroni correction did not identify statistically significant differences between any pair of regions. Therefore, regional variation should be considered exploratory and not be interpreted as evidence of confirmed geographical differences in SBV exposure. Conclusions This study provides serological evidence of prior SBV exposure among ruminants. Seropositivity indicates prior exposure to SBV and does not establish a causal relationship between SBV infection and abortion. Although regional differences in mean antibody titres were observed descriptively, these patterns should be regarded as exploratory, as pairwise regional comparisons did not remain statistically significant after correction for multiple testing. Larger, population‐based studies with balanced sample sizes are required to clarify the geographical patterns of SBV in Iran.