Abstract: 【Objective】Bovine viral diarrhea virus(BVDV) is commonly recognized as an important pathogen for the cattle and causes significant economic losses in the cattle industry worldwide. To assess the overall prevalence of BVDV in Chinese free- roaming beeves, the free-roaming beeves in the Western China were used in the present study by the methods of serological and bioinformatic analysis. Then, the genetic diversity of BVDV was analyzed. This study will provide a theoretical basis for the development of reasonable prevention and control, and for the vaccine development. 【Method】 A total of 1 332 sera were collected in Yunnan, Xinjiang, Gansu and Inner Mongolia from 2014 to 2015. These samples were analyzed by the commercial antibody (Ab) detection kits, and the Ab positive rate of BVDV in various regions were summarized up. Meanwhile, the positive or suspicious samples, whose S/P were less than 60%, were further detected by the Ag detection kit. Then, to isolate BVDV, the positive samples were inoculated into the MDBK cells and passaged by five generations. In addition, the primer designed based on the 5′-UTR of BVDV which has low frequency variability was used to analyze the genetic diversity of BVDV. Then the nucleotide sequences were analyzed by the bioinformatic softwares, including Sequencher4.2, BLAST, ClustalX and MEGA5.2. Finally, the genotypes and phylogenetic analysis of sequenced BVDV were confirmed based on the primers.【Result】Results showed that the average Ab positive rate of BVDV was 33.93% in the four detected provincial regions. Among them, that in the Inner Mongolia was the highest (71.43%), that in Xinjiang taking the second place (57.69%), that in Gansu was the third (16.54%) and that in Yunnan was the lowest (10.0%). The average Ag positive rate of BVDV was only 1.58%, that in Xinjiang was the highest. In this study, a total of 13 BVDV strains were isolated, they were named as Gansu 120, Mongolia 1369, Yilihuoqing 12953, Yillihuoqing 12960, Yilihuoqing 12981, Bozhoujinghe 13001, Bozhoujinghe 13023, Bozhoujinghe 13033, Xinjiangqitai 13041, Xinjiangqitai 13042, Xinjiangqitai 13191, Xinjiangqitai 13220, and Xinjiangqitai 13251, respectively. The polygenetic analysis indicated that these isolates could be mainly classified into four subtypes: BVDV-1q and BVDV-1f (isolated in Xinjiang), BVDV-1m (isolated in Inner Mongolia) and BVDV-1u which was a new subtype isolated in Gansu.【Conclusion】The serological analysis indicated that, although the free-range beef cattle overall Ab positive rate in the four provinces (autonomous regions) was lower than the national average, their situation was different. The high Ab positive rate of Inner Mongolia and Xinjiang indicated that BVDV is prevalent in the free-roaming beeves, and it is essential to minimize the damage by valuable controlling methods. The phylogenetic tree based on 5′-UTR sequence indicated that various genotypes of BVDV were existed in various regions. Overall, the diversity, cross-species transmission, cross-regional transmission and high mutation rate of BVDV make a great challenge for the immunity of vaccine. The significance of this study is to evaluate the prevalence of BVDV in free-range beef cattle through the method of healthy cattle random sample detection and analysis in various regions, and provide the reference for the prevention strategies.

Key words: bovine viral diarrhea virus (BVDV), free-roaming beef cattle, enzyme linked immunosorbent assay (ELISA), positive rate, genotyping