Detection and assessment of antibodies against bovine viral diarrhea virus in swine serum using the virus neutralization assay

The Bovine viral diarrhea virus (BVDV) infections in swine are an important issue to the swine industry due to cross-reaction in serological exams, with the Classical swine fever virus (CSFV) resulting in false-positives. This paper focused on reporting and comparing antibody titers detected in swine serum samples using the virus neutralization assay (VN). To this, 3,084 swine serum samples of 115 swine herds of eight Brazilian states were tested using the VN with BVDV-1 strain Singer and BVDV-2 VS253. Anti-BVDV antibodies were detected in 133 samples (4.31%), 75 (2.43%) were positive when using the BVDV-1 in the assay and 58 (1.88%) were reagent when using the BVDV-2. At herd level, 44.35% (51/115; CI 95%: 35.27-53.43%) had at least one positive animal regardless the species of the virus. The results show that low antibody titer were significantly more frequent than the high ones. Antigenic diversity among the strains used in the VN and the one circulating in swine, and vaccine contamination with BVDV could be involved in the high frequency of low titers. In conclusion, antibodies anti-BVDV were detected in swine of different Brazilian regions. Animal health authorities should be aware of the risk of false positive results to CSF.