Description of anti-BVDV antibodies titers detected in swine serum by virus neutralization assay

The members of the Pestivirus genus are antigenically related, consequently cross-infections, such as BVDV infections in swine, are often reported. The virus neutralization assay (VN) is the standard diagnostic assay for BVDV infections in cattle according to the OIE. However, very little information is available in the scientific literature about the use of VN to detect and quantify antibodies anti-BVDV in swine serum. This study focused on describing our experience and obtained results in the detection of antibodies anti-BVDV in swine serum using the VN.

A set of 3,057 serum samples of swines from eight Brazilian states (Goiás, Mato Grosso do Sul, Mato Grosso, Paraná, Rio Grande do Sul, Santa Catarina, Rio Grande do Norte and São Paulo) were tested in duplicates using the VN to detect antibodies anti-BVDV. The assay was performed according to the Manual of Diagnostic Tests and Vaccines for Terrestrial Animals, using MDBK (Madine Darby Bovine Kidney) tissue culture cells. Both cytopathic strains Singer (BVDV-1) and VS253 (BVDV-2) were used in a 100 TCID₅₀ concentration. The positive samples were those in which occurred total neutralization of the 100 TCID50 in a dilution higher than 1:10. The antibody titer considered was the reciprocal of the highest dilution in which there were total neutralization of the viral dose and the final titer obtained by the geometric mean of the two results.

Out of all tested samples, 2.49% (76) were positive when using the BVDV-1 (Singer) as standard virus. Thus, 36.84% (28/76) of the animals had antibody titer 10; 25.0% (19/76) presented titer 14.14213562; 17.10% presented titer 20; 2.63% (2/76) had 28.28427125; 5.26% (4/76) had titer 40; 3.94% (3/76) had titer 80; 3.94% (3/76) had titer 160; 1.31% (1/76) had antibody titer of 320 and 3.94% (3/76) had titer 640. When using the BVDV-2 (VS253), 1.9% (58) samples were positive and regarding to the titer distribution, 69.0% (40/58) presented antibody titer 10; 13.80% (8/58) presented final titer value of 14.14213562; 10.34% (6/58) presented titer 20; 1.72% (1/58) had titer 56.56854249; 3.44% (2/58) had titer 40 and 1.72% (1/58) had titer 80.

It was possible to notice that lower titer values were the most common in the tested samples, a fact that could be related to unspecific antibody reaction or even with the fact the swine not being the main host specie for the BVDV. The VN assay was able to detect several variations in the serum antibody titer preliminary suggesting that such diagnostic method is suitable for detecting and quantifying anti-BVDV antibodies in swine serum. This study had financial support provided by grant 2014/13590-3, São Paulo Research Foundation (FAPESP).

Disclosure of Interest: None Declared.