Antibody Titers from Finisher Populations with Persistent/Latent PCV2 Infection Before, During and After the PCV2-SD Epizootic

Abstract

Porcine circovirus type 2 (PCV2) diseases (PCVDs) have affected pig production worldwide over the last three decades. Since the advent of mass vaccination, manifestations of PCVDs have dramatically decreased. Nevertheless, persistent/latent PCV2 infections linger in the pig population.Therefore, we investigated whether conclusions can be drawn regarding the health status of a population based on humoral responses to a persistent pathogen such as PCV2. We examined the Swiss finisher population because in this population, time points associated with major events have been well documented. We measured PCV2-specific antibody titers of finishers before the Swiss epizootic in 1996-97 and compared these titers with antibody titers in 2006, during the peak of the epizootic, and in 2011, three years after the start of the mass vaccination of piglets.Two hundred serum samples from finishers were analyzed for each of these time periods, which correspond to before, during and after the Swiss epizootic. PCV2-specific IgG antibody titers were low to modestly positive during the pre-epizootic and post-epizootic periods. At the peak of the epizootic in 2006, almost all serum samples were positive, with higher average IgG concentrations than those detected in pre-epizootic and post-epizootic samples. Moreover, IgM antibodies were analyzed for 60 randomly chosen finishers in each time period. Of these 180 samples, only two serum samples from 2006 contained PCV2-specific IgM antibodies.Mass vaccination against PCV2 reduced PCV2-specific antibody titers in pigs with persistent/latent infection to pre-epizootic levels. Our data show prevalence for and concentrations of IgG-specific PCV2 antibodies, which appear to be correlated with PCVD. This result is counterintuitive because one would typically expect higher antibody concentrations to be associated with less disease; a possible interpretation is that elevated concentrations of immature anti-PCV2 antibodies provided pigs with a certain level of protection against PCVDs.Keywords: PCV2-specific IgG and IgM; Population study; Seroprevalence; Persistent/latent infections; Epizootic periods; Mass vaccination campaign Short CommunicationPorcine circovirus type 2 (PCV2), which is one of the most significant pathogens in pig production worldwide, is the causative agent of porcine circovirus diseases (PCVDs). PCV2 can be detected in both healthy and diseased pigs [1] and is found in the lymphatic system in most pigs [2,3].We and others have demonstrated that PCV2 affects the maturation and differentiation of T cells [3][4][5]. We specifically identified T helper cells as being targeted by PCV2-infected cells in the thymus [4]. These T helper cells are essential for the proper maturation of high-affinity antibody-secreting centroblasts [6]. Overall, humoral responses to PCV2 do not correlate with the infection statuses of pigs [4,7,8].This result is unsurprising due to the latent nature of PCV2, which is found in pig fetuses before immune competency [3,4]. In addition, current infor...