<![CDATA[African horse sickness (AHS) is a severe Culicoides-borne viral disease of equids caused by African horse sickness virus (AHSV), with potentially high mortality and important implications for animal health, equine movement, and trade. The emergence of AHSV-1 in Thailand in 2020 demonstrated the risk of transboundary introduction into previously unaffected Southeast Asian equine populations. Although AHS has not been reported in Indonesia, baseline surveillance remains important for preparedness. Probolinggo Regency recorded 352 horses in 2023, the largest horse population among regencies and municipalities in East Java. This study estimated observed AHSV antibody seroprevalence using an official AHS surveillance laboratory report from Balai Besar Veteriner Wates. A cross-sectional analysis included 136 horse serum sample records from nine subdistricts. The report recorded sample collection on 20 November 2025, specimen submission and receipt on 24 November 2025, and AHS ELISA antibody testing on 27 November 2025. All 136 samples were seronegative according to the laboratory interpretation criterion (seropositive >70%; seronegative ≤70%), yielding an observed apparent seroprevalence of 0% (0/136) and a one-sided 95% Clopper-Pearson upper confidence limit of 2.18%. This limit assumes independent random sampling and perfect diagnostic classification and does not account for non-probability, spatially clustered sampling or unknown ELISA sensitivity and specificity. Individual horse identifiers were unavailable, so 136 samples could not be confirmed to represent 136 unique horses. These findings provide baseline surveillance evidence but not definitive evidence of disease freedom. Continued risk-based surveillance integrating serology, molecular diagnostics, animal movement data, and vector monitoring is warranted.]]>
