Surveillance and genetic diversity of bovine viral diarrhea virus in dairy herds across Taiwan.

Bovine viral diarrhea virus (BVDV) significantly impacts cattle worldwide, causing respiratory, gastrointestinal, and reproductive disorders that lead to substantial economic losses. Despite its high global prevalence and various genotypes, the infection status of BVDV in Taiwan has not been reported. This study conducted large-scale surveillance in 2014, analyzing 460 bovine serum samples collected from 49 dairy herds across Taiwan. The results revealed a herd-level seroprevalence of 59.2 % (29/49), with significant regional variations: 16.7 % in the northern region and 77.8 % in the southern region. At the animal level, the overall BVDV-positive rate was 32.4 % (148/460), ranging from 3.3 % (northern region) to 41.5 % (central region), with significant regional differences as analyzed by the mixed-effects logistic regression model. Five-year surveillance of a single dairy farm revealed persistent BVDV circulation, with the seroprevalence starting at 89 % in 2019 and remaining between 82 % and 100 % among the cohort of 27 cattle monitored from 2020 to 2023. In contrast, a study of three farms revealed that while the two high-prevalence farms maintained high infection rates, the low-prevalence farm experienced a gradual decline in infections, indicating varied infection dynamics. Moreover, this study identified BVDV-1b as the predominant genotype in Taiwan, along with BVDV-1a and BVDV-2a, which were detected in mosquito samples. These findings emphasize the high prevalence of BVDV in Taiwan, ongoing viral circulation within herds, and the need for continuous surveillance and robust control measures to mitigate the spread of BVDV in Taiwan's cattle industry.