Field Study on the Immunological Response and Protective Effect of a Licensed Autogenous Vaccine to Control Streptococcus suis Infections in Post-Weaned Piglets

Abstract

Streptococcus suis is one of the most important bacterial pathogens in weaned piglets and responsible for serious economic losses to the swine industry. Currently, mostly autogenous vaccines composed of killed bacteria (bacterins) are available. However, immunological and protective data from field studies are missing. We report for the first time a comparative field study on the immunological response induced by an autogenous vaccine applied to either piglets or sows in a farm with recurrent S. suis problems. (I) Piglets from non-vaccinated sows received an autogenous bacterin during the first week and at three weeks of age. (II) Sows received the vaccine at five and three weeks pre-farrowing and piglets were non-vaccinated. Levels, isotype profile and opsonophagocytosis capacity of the serum antibodies induced by vaccination were evaluated. Vaccination of piglets failed to induce an active immune response. Vaccination of sows induced a significant increase in anti-S. suis antibodies, mainly composed of IgG1. However, isotype switching was modulated by the S. suis serotype included in the vaccine formulation. Despite this antibody increase in vaccinated sows, transfer of maternal immunity to piglets was not different from the control group (i.e., piglets from non-vaccinated sows). Notably, levels of maternal antibodies in piglets were already very high with marked opsonophagocytosis capacity at one week of age, independently of the vaccination program. However, their levels decreased by three weeks of age, indicating possible absence of antibodies in the post-weaning high-risk period. These observations correlated with lack of clinical protection in the farm. Overall, a piglet or a sow vaccination program herein mostly failed to induce lasting protection in nursery piglets. An improvement of vaccine formulation or an optimized program may be required.

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

“…These antibodies (either due to natural exposition and/or vaccination) were highly opsonic, and thus able to eliminate S. suis in an in vitro test. Similar findings were observed in a recent field study using autogenous vaccination of sows from a herd that was also experiencing S. suis serotype 7 clinical problems [ 16 ].…”

“…However, scientific studies regarding their ability to confer protection are missing. To the best of our knowledge, only three field studies are available on the efficacy of this preventive approach using autogenous bacterins manufactured by licensed companies [ 14 – 16 ]. Moreover, it is crucial to highlight that autogenous bacterin manufacturing differs from laboratory-made bacterins used in experimental studies.…”

“…Moreover, it is crucial to highlight that autogenous bacterin manufacturing differs from laboratory-made bacterins used in experimental studies. Indeed, several works have evaluated the immunogenicity or protective capacity of experimental bacterins under controlled vaccination/challenge studies [ 9 , 11 , 13 ], but only very few have analyzed the immunogenicity and/or clinical protection using licensed autogenous vaccines under field conditions [ 14 – 16 ]. Overall, results from these studies are controversial, highlighting the importance for more research in this area [ 11 ].…”

Comparative Study of Immunogenic Properties of Purified Capsular Polysaccharides fromStreptococcus suisSerotypes 3, 7, 8, and 9: the Serotype 3 Polysaccharide Induces an Opsonizing IgG Response

“…One study has shown that purified CPS 2 can induce anti-CPS 2 specific antibodies in swine, but when using Freund's Complete Adjuvant (43). One single study has reported low levels of anti-CPS 7 in naturally exposed piglets (72) CFU/ml. Heat-killed bacterial cultures were obtained as previously described (73).…”

“…One study has shown that purified CPS 2 can induce anti-CPS 2 specific antibodies in swine when using Freund's complete adjuvant ( 43 ). A single study has reported low levels of anti-CPS 7 in naturally exposed piglets ( 72 ). Therefore, swine seems to have a B cell repertoire able to recognize, at least, CPSs 2 and 7.…”