الفهرس 
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Abstract
Bovine viral diarrhea (BVD) is one of the most economically significant diseases in the bovine industry causing losses due to diarrhea, reproductive disorders, immunosuppression and mortalities. The aim of our investigation was to detect and subtype BVDV from calves on 2 dairy cattle and 2 buffalo farms in Ismailia province, Egypt as an indicator of BVDV infection status in the province. A total of 298 blood samples were collected and tested using an optimized one-step probe based QRT-PCR. All the positive samples by the multiplex QRT-PCR were tested using conventional RT-PCR to amplify multiple areas of the genome for further phylogenetic analysis and subtyping. Thirty-nine (13.1%) of the tested samples were positive for BVDV-1. Only three samples, all from a single dairy cattle farm, had enough viral RNA to be amplified by RT-PCR. The PCR products were sequenced and phylogenetic analysis revealed detection of BVDV-1b. The detected strain is closely related to worldwide BVDV-1b strains and strains detected as a contaminant to mammalian cell lines, making it difficult to trace its origin. For further characterization about 20 overlapping primers were designed for complete genome sequencing. The nucleotide and deduced amino acids sequences alignment of coding regions in comparison to other published BVDV-1b strains revealed homology ranged from 89.4% to 94.2% and 91.3% to 96.8%, respectively. The E2 glycoprotein was highly divergent, with nucleotide and amino acid homology ranging from 81.3% to 93.6% and 85.3% to 93.6%, respectively. Furthermore, the nonstructural glycoprotein 3 (NS3) was highly conserved, with nucleotide and amino acid homology from 90.9% to 95.1% and 98% to 99.4%, respectively. To our knowledge, this is the first report describing the circulation of BVDV-1b in Egyptian dairy cattle population.