Persistent BVD virus infections in offspring from imported heifers.

The aim of this study was to investigate the possible risk of bovine viral diarrhea virus transport from imported live animals. For this purpose, two different groups of animals were sampled in this study. Group 1 consisted of pregnant heifers; group 2 consisted of male beef cattle imported during 2011-2012 and 2015, respectively. Blood samples were tested for pestivirus antigen using a commercial BVDV antigen ELISA. All the pregnant heifers were negative, but 9 out of 412 offspring and 5 of the 332 male cattle were BVDV antigen positive. Virus isolation and also investigation by RT-PCR were carried out by using 14 ELISA-positive samples. At the end of three blind passages, eight non-cytopathogenic isolates were obtained by indirect immunoperoxidase monolayer assay, which were also RT-PCR positive using panpesti-virus primers. After discriminative RT-PCR, all the isolates that were identified as BVDV-1 and 5'UTR-based analysis demonstrated the existence of BVDV-1b (n = 4), BVDV-1f (n = 2), BVDV-1 l (n = 1), and BVDV-1r (n = 1) subgenotypes. There was no BVDV subgroup that is newly introduced into the country. However, detection of persistent infection in calves born from imported animals demonstrates the risk of BVDV virus introduction by imported animals into the receiving country. Viral strains from persistently infected animals were characterized as BVDV-1b, which is predominant subgroup in the country where animals are imported. These results highlight a possible problem for the areas where a BVDV control program is currently ongoing. Additionally, sequences obtained in this study also showed that there are two distinct branches identified in BVDV-1l.