Antigenicity of bovine parvovirus in fetal infections

The humoral immune response of bovine fetuses to bovine parvovirus (BPV) infection during the 2nd and 3rd trimesters was studied by the single radial immunodiffusion, hemagglutination-inhibition (HI), indirect immunofluorescence (IFA), microneutralization (MN), plaque-neutralization, and double immunodiffusion (DID) tests. Serum samples collected from 23 BPV-inoculated and several control fetuses were tested. The immunoglobulin (Ig) M concentrations reached 355 mg/100 ml at 10 days after fetal inoculations were done and then decreased. The IgG concentration increased 10 days after inoculation and was maximal 142 days later. A correlation between Ig concentrations and antibodies reacting in the HI, IFA, MN, DID, and plaque-neutralization tests existed in all samples. Neutralizing and HI antibodies were detected 10 days after fetal inoculations. The highest MN titer of 4,096 was detected in a fetus 10 days after the inoculation done during the 3rd trimester. Six serum samples were positive in the IFA test. These samples, collected 10 to 60 days after fetuses were inoculated, had IgG concentrations of 615 mg/100 ml or higher, and had titers of 16 to 64. Treatment of BPV with carbonate-bicarbonate buffer (pH 10.5) disrupted the virus and liberated antigens reacting in the DID test. Electron microscopic examination of the negatively stained antigen preparation revealed loss of structural integrity of the viral particles. This suspension of disrupted BPV was reactive with some of the fetal serum samples in the DID test, inducing 1 or 2 precipitin lines.