Immunogenicity study of a Streptococcus suis autogenous vaccine in preparturient sows and evaluation of passive maternal immunity in piglets

Abstract

Background Streptococcus suis is an important pathogen that causes severe diseases mostly in weaned piglets. Only available vaccines in the field are those composed of killed bacteria (bacterins) but data about their effectiveness are missing. We report here a field study on the immunological response induced by an autogenous vaccine applied in pre-parturient sows. Using a farm with recurrent S. suis serotype 7 problems, the study was divided in three experiments: (I) Sows received the vaccine at 7 and 3 weeks pre-farrowing. (II) Replacement gilts introduced to the herd received the vaccine at 4 and 7 weeks after their entry in quarantine and a boost 3 weeks pre-farrowing. (III) Gilts from experiment II received another boost 3 weeks pre-farrowing at their 3rd/4th parity. Levels, isotype profile and opsonophagocytosis capacity of the serum antibodies induced by vaccination were evaluated in sows and maternal immunity in piglets. Results In sows (I), the vaccine induced a slight, albeit significant, increase in anti-S. suis total antibodies after 2 doses when compare to basal levels already present in the animals. These antibodies showed a high opsonic capacity in vitro, highlighting their potential protective capacity. A gilt vaccination program of 3 doses (II) resulted in a significant increase in anti-S. suis total antibodies. Levels of maternal immunity transferred to piglets were high at 7 days of age, but rapidly decreased by 18 days of age. A gilt vaccination program ensued a higher transfer of maternal immunity in piglets compared to control animals; nevertheless duration was not improved at 18 day-old piglets. The vaccine response in both gilts and sows was mainly composed of IgG1 subclass, which was also the main Ig transferred to piglets. IgG2 subclass was also found in piglets, but its level was not increased by vaccination. Finally, a recall IgG1 response was induced by another boost vaccination at 3rd/4th parity (III), indicating that the vaccine induced the establishment of a lasting memory response in the herd. Conclusions Overall, an optimal gilt/sow vaccination program might result in increased antibody responses; nevertheless duration of maternal immunity would not last long enough to protect post-weaned piglets.

Experimental evaluation of protection and immunogenicity of Streptococcus suis bacterin-based vaccines formulated with different commercial adjuvants in weaned piglets

“…Vaccine interference with maternal antibodies has specifically been suggested for S. suis [ 23 ]. As previously reported, piglets used in the current study possessed maternal antibodies, since most sows are colonized by S. suis (or S. suis -like microorganisms) and normally possess high levels of antibodies [ 13 , 23 , 25 ]. High basal levels of maternal antibodies reacting with whole bacteria of S. suis serotype 2 were still present at weaning, which might explain the fact that one-dose immunization was not sufficient to induce a significant increase in specific anti- S. suis antibodies in vaccinated piglets and this independently of the adjuvant used.…”

“…These antibodies might have been generated in adult animals by S. suis strains that are part of the normal microbiota or even by other S. suis -like microorganisms that are present in the upper respiratory tract [ 3 , 24 ]. Adult animals usually present high levels of antibodies tested for any serotype of S. suis [ 13 , 25 ] (unpublished observations), which may explain why S. suis -associated diseases are almost never observed in older animals [ 10 ]. Finally, in addition to the presence of some residual maternal antibody interference, other features that might also explain the lack of immunological response after one vaccine dose include an immature immune system, diet change, and other stressing factors [ 26 , 27 ].…”

Immune response induced by a Streptococcus suis multi-serotype autogenous vaccine used in sows to protect post-weaned piglets

“…Absence of protective responses from these vaccines have been attributed to the failure of whole-bacterial antigens to elicit an immune response due the inactivation processing, production of antibodies to antigens not associated with protection, and/or the use of inappropriate adjuvants [ 6 , 11 , 16 ]. Indeed, it is difficult to compare published studies with different autogenous vaccines [ 12 – 14 ], as they may use different adjuvants, bacterial concentrations as well as conditions used to make the pathogen grow and bacterial killing methods, among other variables. In addition, no field studies have evaluated the usefulness of an autogenous vaccine in the complete absence of antimicrobials on the farm.…”

“…However, published studies on the use of autogenous vaccines in the field showed so far limited and/or no increase of passive maternal antibodies in piglets during the nursery barn period [ 11 – 13 ]. Two of these published field studies used vaccines manufactured within the same commercial vaccine company [ 12 , 13 ]. Further research on length and duration of passive maternal immunity elicited by vaccines produced by different manufacturing companies is required.…”

Synthesis of Oligosaccharides Resembling the Streptococcus suis Serotype 18 Capsular Polysaccharide as a Basis for Glycoconjugate Vaccine Development

“…A glycoconjugate vaccine candidate against S. suis serotype 2 (SS2) based on isolated CPS and semisynthetic glycoconjugate vaccine candidates for SS2, SS3, SS9, and SS14 have been evaluated. , The S. suis serotype 18 CPS pentasaccharide repeating unit provides an interesting challenge for synthetic chemists as a first step toward a glycoconjugate vaccine for this serotype. The SS18 pentasaccharide repeating unit made up of [→3)- d -GalNAc­(α1-3)­[ d -Glc-(β1-2)] d -GalA4OAc­(β1-3)- d -GalNAc­(α1-3)- d -BacNAc4NAc­(α1→] n (Figure a) requires the installation of a 1,2- cis linkage between d -bacillosamine and the reducing-end linker. The central galacturonic acid branching unit is a challenge concerning the poor reactivity and protecting group orthogonality.…”