First detection of African swine fever in a swine farm in Taiwan.

Introduction: African swine fever (ASF) is a highly contagious, high-consequence transboundary animal disease that poses a critical threat to global swine production and agricultural economics. Since its emergence in China in 2018, ASF has spread to over 20 Asia-Pacific countries, causing significant economic disruption. While Taiwan previously detected ASF virus several times in dead pigs drifting offshore, or in illegal pork-related products brought by international tourists and inspected at airport and seaport border controls, no local domestic swine farm had tested positive before this October 2025 ASF event. However, maintaining this disease-free status requires constant vigilance against evolving regional biosecurity threats. Methods: The first ASF detection in a domestic swine herd in Taichung City, Taiwan, reported on October 22, 2025, was triggered by abnormal alerts of the monitoring system in the rendering plant; the index farm captured a cumulative herd mortality rate of 35.2% that exceeded the predefined threshold (3% mortality daily in the nursery to finish pigs). Five finisher pigs were submitted for diagnostic evaluation, which subsequently confirmed ASFV infection via real-time PCR, pathological examination, immunohistochemistry, virus isolation, and whole-genome sequencing. Results: Affected pigs showed clinical signs including wheezing, sudden death, nasal bleeding, uncoagulated blood in the nostrils, and mild hemorrhage on the skin surface of the neck, abdomen, and buttocks. Histopathological examination revealed severe multisystemic hemorrhagic lesions. Based on assay results of the P72, P54, P30, and CD2v genes, and whole-genome sequence, phylogenetic analysis confirmed that the isolate (ASFV/TWN/2025) is a genotype I/II recombinant strain, most similar to prevailing strains isolated in China and Vietnam, sharing 99.95%-99.97% and 99.92%-99.97% nucleotide similarity of whole genome sequence, respectively. Discussion: Upon confirmation of the ASF case, authorities immediately implemented a nationwide swine movement standstill for 15 days to mitigate transmission risk. To date, no secondary cases have been detected. This article details the early monitoring and rapid diagnosis process of the first case of ASF infection in a farm in Taiwan, and highlights the information from this case to provide lessons for disease diagnosis and prevention in ASF-free areas.