A follow-up investigation of the reported high herd prevalence of bovine viral diarrhea in dairy farms in Georgia and Florida

Bovine viral diarrhea virus (BVDV) causes economically significant disease in the dairy industry worldwide. Testing and removing persistently infected (PI) animals is an es­sential part of controlling BVD in infected herds. A previous surveillance study using bulk-tank milk testing by real-time RT-PCR revealed a herd prevalence of 38.4% in Georgia and Florida. The high herd prevalence of BVD in these dairy farms prompted subsequent investigation to update the prevalence and reveal the subtype of the circulating BVDV in the region. Ninety bulk milk samples from 37 dairy farms were tested during 2021-2022. A survey related to management practices was also conducted. Overall, 10.0% of the bulk milk samples tested positive (9/90) and 10.8% of the herds tested positive (4/37). The sequences of 5’- untranslated and E1-E2 regions of the viral genome from positive samples all matched to the subtype of BVDV-1b. Phylogenetic analysis indicates these BVDVs are regional circulating strains. Most farms routinely use vaccines in calves (83.8%) and cows (89.2%) to reduce virus transmission and prevent clinical diseases and PI animals. However, only 24.3% and 27.0% of the farms test for BVD in re­placement heifers and newborn calves, respectively. And none of the farms quarantine newly purchased animals. Despite high vaccination rate, BVD can still be an issue for dairy farms in the southeast region of the United States, exemplifying the importance of PI animals’ removal and biosecurity procedures implementation to efficiently control BVD in dairy herds.