Genotypes of Bovine Viral Diarrhea Virus Infecting Vaccinated and Nonvaccinated Cattle in Thrace District, Türkiye.

Bovine viral diarrhea virus (BVDV) is a major cause of economic losses in the global cattle industry. This study investigated the clinical involvement and genetic diversity of BVDV in clinically affected cattle from the Thrace region in Türkiye, a critical border area with the European Union. A total of 533 nasal and rectal swabs were collected from 26 farms exhibiting clinical respiratory disease or diarrhea and analyzed using real-time RT-PCR. Positive samples were further characterized by sequencing and phylogenetic analysis to determine viral genotypes and subgenotypes. BVDV RNA was detected in 9 out of 26 farms (34.6%), with an overall positivity rate of 17.8% (95/533). Statistical analysis revealed significant associations between PCR positivity and both sampling year (p < 0.05) and animal age (p < 0.05). Genetic analysis of partial 5'-UTR sequences identified nine Pestivirus bovis subgenotype 1a strains, one Pestivirus bovis subgenotype 1f, and one Pestivirus brazilense. The Pestivirus bovis 1a strains clustered distinctly from previously reported Turkish BVDV-1 isolates, showing 97.32-99.11% nucleotide similarity with strains from Türkiye, Germany, China, Japan, the USA, Iran, and Argentina. Among the 533 samples tested, one Pestivirus brazilense isolate was identified, indicating its rare occurrence in the studied population despite targeted screening. This study represents the first report of Pestivirus brazilense in the Thrace region of Türkiye, expanding its known geographic range. The epidemiological data and genetic diversity analysis of BVDV strains characterized in this study offer critical insights for refining BVDV control programs, informing regional risk assessment, and supporting vaccine development.