A critical review speculating on the protective efficacies of autogenous Streptococcus suis bacterins as used in Europe

Abstract

Background: Streptococcus (S.) suis is a major porcine pathogen causing high morbidity worldwide. This includes well-managed herds with high hygiene standards. In Europe, no licensed vaccine is available. As practitioners are obliged to reduce the use of antibiotics, autogenous S. suis vaccines have become very popular in Europe.Main body: Autogenous vaccines (AV) are generally neither tested for safety, immunogenicity nor protective efficacy, which leads to substantial uncertainties regarding control of disease and return on investment. Here, S. suis publications are reviewed that include important data on epidemiology, pathologies and bacterin vaccination relevant for the use of AV in the field. Differences between herds such as the porcine reproductive and respiratory syndrome virus infection status and the impact of specific S. suis pathotypes are probably highly relevant for the outcome of immunoprophylaxis using autogenous S. suis bacterins. Thus, a profound diagnosis of the herd status is crucial for management of expectations and successful implementation of AV as a tool to control S. suis disease. Induction of opsonizing antibodies is an in vitro correlate of protective immunity elicited by S. suis bacterins. However, opsonophagocytosis assays are difficult to include in the portfolio of diagnostic services. Conclusion:Autogenous S. suis bacterins are associated with limitations and risks of failure, which can partly be managed through improvement of diagnostics.

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

“…Immunization of preparturient sows might elicit protective passive maternal immunity to their progeny and can be an attracting alternative to piglet vaccination [ 9 ]. However, results from vaccinated sows with bacterins are also matter of controversy [ 5 , 9 – 11 ].…”

“…Independently of the vaccination program (sow vs. piglets), the limited protective response generally observed with bacterins can be explained by many hypotheses. For example, fixation with formalin or heat treatment might degrade bacterial epitopes and consequently vaccine immunogenicity [ 11 , 12 ]. Bacterial concentration and number of vaccine doses would also be a limiting factor, with repeated immunizations probably required to induce protection [ 12 ].…”

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

“…These vaccines are bacterins (whole cell killed bacteria with a complex antigen charge) based on the predominant strain(s) recovered from diseased pigs in the affected farm and produced by accredited laboratories. Most studies evaluating the protective capacity of bacterins have been carried out under laboratory conditions with vaccines produced with reference strains and presented contradictory results [ 7 , 11 ]. The limited protective response obtained with experimental bacterins has been attributed to failure of the whole-bacterial antigens to elicit an immune response due to loss of antigenicity caused by the killing procedure, to production of antibodies to antigens not associated with protection and/or the use of inappropriate adjuvants [ 7 , 11 ].…”

Population structure, genetic diversity and pathotypes of Streptococcus suis isolated during the last 13 years from diseased pigs in Switzerland

“…The most important CCs implicated in human infections are the following: CC1 (harboring most important ST1) in Europe, Asia, North- and South America, and Africa [ 28 ]; CC20 in the Netherlands [ 11 ]; CC25 and CC28 in North America, Australia, and Asia [ 28 ], although in the United States an increasing trend of the genetically diverse CC94 was observed [ 29 ]. In Europe, a high prevalence of virulent mrp + epf + sly + cps2 strains being part of CC1 and mrp * cps 9 strains of CC16/87 can be noticed [ 30 ].…”