Decay of Maternally Derived Antibodies and Seroconversion to Respiratory Viral Infection in Pig Herds

This study investigated the decay of maternally derived antibodies to pseudorabies virus (PRV), porcine reproductive and respiratory syndrome virus (PRRSV), porcine circovirus type 2 (PCV2) and swine influenza virus (SIV) in the pig herds in Taiwan. Additionally, the serological profiles of these viral pathogens were examined in a cross-sectional study of six pig populations. The observed half lives of maternally derived serum neutralization antibodies against PRV and PRRSV were 2.0 and 3.0 weeks, respectively. The estimated times to seronegativity to PRV and PRRSV were 12.2 and 10.4 weeks, respectively. At one week of age, over 80% of pigs were positive for PCV2 and hemagglutinin 1 (H1) SIV antibodies, but antibody decreased to undetectable levels at 11 and 5 weeks of age, respectively. Except for SIV infection, which probably exhibited sporadic, mild to moderate outbreaks, the most common sequence of seroconversion to the viral respiratory infections in the six pig herds appear to be in an order of PCV2, followed by PRRSV and PRV. The results of this study provide basic data needed to design effective vaccination programs and intervention strategies for controlling swine respiratory diseases.