Immunogenicity of an AutogenousStreptococcus suisBacterin in Preparturient Sows and Their Piglets in Relation to Protection after Weaning

Abstract

Streptococcus suis is an important porcine pathogen causing meningitis and other invasive diseases in piglets of different ages. Application of S. suis serotype 2 bacterins to specific-pathogen-free (SPF) weaning piglets has been demonstrated to protect against the homologous serotype. However, autogenous S. suis bacterins are also applied to sows and suckling piglets in the field. Therefore, comparative evaluation of different bacterin immunization regimes, including sow vaccination, was performed in this study. The main objectives were to determine the immunogenicity of an S. suis bacterin in sows prepartum and its influence on active immunization of piglets. Experimental infection of 6-and 8-week-old weaning piglets was performed to elucidate protective efficacies. Humoral immune responses were investigated by an enzyme-linked immunosorbent assay (ELISA) measuring muramidase-released protein (MRP)-specific IgG titers and by opsonophagocytosis assays. Bacterin application elicited high MRP-specific IgG titers in the serum and colostrum of sows, as well as opsonizing antibodies. Piglets from vaccinated sows had significantly higher MRP-specific titers than respective piglets from nonvaccinated sows until 6 weeks postpartum. Vaccination of suckling piglets did not result in high MRP-specific titers nor in induction of opsonizing antibodies. Furthermore, neither vaccination of suckling nor of weaning piglets from immunized sows was associated with a prominent active immune response and protection at 8 weeks postpartum. However, protection was observed in respective 6-week-old weaning piglets, most likely because of protective maternal immunity. In conclusion, this study provides the first results suggesting protective passive maternal immunity for S. suis serotype 2 after bacterin vaccination of sows and a strong inhibitory effect on active immunization of suckling and weaning piglets, leading to highly susceptible growers.Streptococcus suis causes various pathologies, such as meningitis, arthritis, serositis, bronchopneumonia, and endocarditis (11). Furthermore, S. suis serotype 2 is also an important zoonotic agent (9). S. suis is characterized by a high diversity, and different serotypes might be involved in invasive diseases in pigs (6,24). However, most of the experimental studies have been performed with serotype 2. Based on comparative evaluation of virulence of wild-type strains in intranasal infection experiments, serotype 2 isolates expressing the 136-kDa muramidase-released protein (MRP) and the 110-kDa extracellular factor (EF) are regarded as more virulent than serotype 2 strains which lack these factors or express MRP and a large variant of EF called EF* (22,23). On the other hand, MRP ϩ

Antibody Response Specific to the Capsular Polysaccharide Is Impaired in Streptococcus suis Serotype 2-Infected Animals

“…In vitro studies using either nonencapsulated mutants or highly purified S. suis type 2 CPS have shown that this molecule severely interferes with the activation of the host innate immune system (5-7, 34, 39, 67). In vivo immunization experiments in pigs showed that repeated injections of purified CPS (25) or whole killed S. suis type 2 cells (26,68,69) resulted in no or very low induction in CPS-specific Ab titers in comparison with proteinspecific Ab titers. TLR2 has been implicated as an important innate recognition receptor for S. suis type 2, and both in vitro and in vivo studies have highlighted its role in induction of an inflammatory response (38)(39)(40).…”

The immunoglobulin M-degrading enzyme of Streptococcus suis , Ide Ssuis , is a highly protective antigen against serotype 2

“…However, there are major limitations associated with these bacterins, in particular, (i) most often only partial protection against the homologous serotype is observed, (ii) protection against heterologous serotypes is not elicited, (iii) differentiation of infected and vaccinated animals is generally not possible, and (iv) interference with maternal immunity is very common [9,10]. The latter makes it very difficult to prime piglets earlier than at an age of 4 to 6 weeks in porcine practice.…”

Porcine Dendritic Cells as an In Vitro Model to Assess the Immunological Behaviour of Streptococcus suis Subunit Vaccine Formulations and the Polarizing Effect of Adjuvants

“…A high genetic and phenotypic diversity of S. suis strains within serotype 2 is reported according to geographical distribution [4]. Pigs are affected generally between 5 and 10 weeks of age, when passive immunity provided by colostrum decreases [5,6]. The pathogenesis of S. suis infection is not fully understood.…”