EN
Forty-five cattle of different ages and gender were selected from three separate farms with a total number of 929 animals. Blood serum samples from each of the animals were tested twice at two-month intervals for bovine viral diarrhoea virus (BVDV) antigen (BVDV Ag) and BVDV antibodies (BVDV Ab) using ELISA. Five animals were found to be BVDV Ag positive and BVDV Ab negative. Therefore, their blood and saliva samples were subjected to further investigation. The samples of blood serum and saliva were additionally screened by a nested reverse transcription PCR (RT-nPCR), real-time PCR, and virus isolation to confirm BVDV persistent infection. Viral RNA was isolated from blood and saliva samples. The cDNA was synthesised and amplification of DNA was performed. The results of RT-nPCR were analysed by gel electrophoresis using ethidium bromide while those of real-time PCR were interpreted according to the amplification curve. Laboratory testing of blood and saliva samples revealed 5 persistently infected (PI) animals from one farm with 579 cattle (0.9% prevalence). The results were confirmed by RT-nPCR and real-time PCR screening samples of blood serum. Using PCR techniques and virus isolation, BVDV RNA was detected; however, the level of viral RNA in saliva was found to be lower than that in blood serum. The results obtained show the possibility to identify PI animals by RT-nPCR and real-time PCR techniques from saliva samples. The collection and testing of saliva is a simple and quick technique, and can be successfully applied in field conditions to identify PI animals, avoiding the risk of intervention while sampling blood or dependence on animal gender and lactation period while sampling milk or semen.