Detection, molecular characterisation and investigation of BVDV genotypes in cattle

Bovine viral diarrhea (BVD) is an acute, subclinical and persistent disease caused by bovine viral diarrhoea virus (BVDV) of the genus Pestivirus in the Flaviviridae family, which causes digestive, respiratory and reproductive disorders in cattle. The prevalence of BVDV infection can be high on farm and regional basis due to the difficulties in the detection of persistently infected (PI) animals, the continuous spread of the virus within the herd and the insufficient implementation of BVDV control programmes. Due to the lack of detection of BVDV positive animals and ineffective implementation strategies and programmes for eradication of BVDV, economic losses occur due to decreased milk yield, decreased immunity and secondary infections, decreased reproductive performance and birth anomalies. The aim of this study was to detect BVDV in cattle in Thrace district by real time RT-PCR, molecular characterisation, determination of genotypes circulating in cattle and isolation of the virus. For this purpose, cattle farms in Thrace district, Marmara Region were visited. Nasal and faecal swabs were taken from 533 animals with respiratory problems and diarrhoea symptoms in the visited farms. Of these animals, 258 had only respiratory problems, 156 had only diarrhoea and 119 had diarrhoea and respiratory problems. Following the examination of the samples by real time RT-PCR, sequence and phylogenetic analyses were performed by RT-PCR from the positive samples. Virus isolation was performed in MDBK cell culture from the samples with low Ct value. In this study, Pestivirus-RNA was detected by real time RT-PCR test in 50 (18.2%) of 274 samples from which faecal swabs were taken and 45 (17.4%) of 259 samples from which nasal swabs were taken. Phylogenetic analyses revealed that 9 of the sequenced samples were BVDV-1a subgenotype, 1 was BVDV-1f subgenotype and 1 was BVDV-3 genotype. BVDV-1f subgenotype was isolated from one nasal swab. In conclusion, real-time RT-PCR test should be used as the first screening test for the detection of BVDV in farms. BVDV-1a and BVDV-1f subgenotypes are circulating in Thrace district as in other regions of our country. This study is the first report on the presence of BVDV-3 genotype in Thrace district. Data obtained in this thesis will contribute to the studies on the follow-up of BVD disease in Turkey in future and to the protection-control studies that can be carried out in a regional basis.