Dynamics of porcine circovirus type 2 infection and neutralizing antibodies in subclinically infected gilts, and the effect on their litters¤

Abstract

Background: porcine circovirus type 2 (PCV2) is associated with reproductive disease in newly populated herds and in replacement breeding stock from new sources and is almost exclusively reported in gilts. Objective: the main purpose of this study was to assess the dynamics of porcine circovirus type 2 infection and neutralizing antibodies in subclinically infected gilts and the effect on their piglets. Methods: the study was conducted with 40 gilts selected at random from four breeding herds. Blood samples, nasal and vaginal swabs were obtained from the gilts at arrival, acclimatization, farrowing, and one day after farrowing. Colostrum samples were collected immediately after parturition and one day after farrowing. Blood, nasal swab, or tissue samples were collected from four piglets prior to suckling. All serums were analyzed by virus neutralization test (VNT) to establish the presence of antibodies. All samples were subjected to SYBER Green real-time PCR assay to detect PCV2 DNA. Results: high levels of viremia and viral load of PCV2 in nasal and vaginal swabs were found in healthy gilts at arriving, confrming the introduction of infected animals into the farms. In addition, most gilts were positive for PCV2 DNA in serum, nasal and vaginal swabs at farrowing. PCV2 shedding was also observed in nasal and vaginal fuids and colostrum even in presence of serum neutralizing antibodies (NA). Subclinically infected dams had detectable viremia, developed anti-PCV2 antibodies, and there was PCV2 DNA in tissue samples of their born alive and healthy piglets. PCV2a and PCV2b genotypes were confrmed in PCV2 subclinical infection in both dams and piglets in utero. Conclusion: replacement gilts can be infected with PCV2 before entering the farm and continuous exposure seems to occur horizontally in acclimatization and gestation units or before farrowing. Exposure and infection during gestation may result in infected but apparently healthy piglets.