Abstract
Streptococcus suis is an important swine pathogen responsible for economic losses to the swine industry worldwide. There is no effective commercial vaccine against S. suis. The use of autogenous (“bacterin”) vaccines to control S. suis outbreaks is a frequent preventive measure in the field, although scientific data on immunogenicity and reduction in mortality and morbidity are scarce. The goal of our study is to experimentally evaluate the immunogenicity and protective efficacy against homologous challenge in weaned piglets of a S. suis serotype 2 bacterin-based vaccine formulated with six different commercial adjuvants (Alhydrogel®, Emulsigen®-D, Quil-A®, Montanide™ ISA 206 VG, Montanide™ ISA 61 VG, and Montanide™ ISA 201 VG). The vaccine formulated with Montanide™ ISA 61 VG induced a significant increase in anti-S. suis antibodies, including both IgG1 and IgG2 subclasses, protected against mortality and significantly reduced morbidity and severity of clinical signs. Vaccines formulated with Montanide ISA 206 VG or Montanide ISA 201 VG also induced a significant increase in anti-S. suis antibodies and showed partial protection and reduction of clinical signs severity. Vaccines formulated with Alhydrogel®, Emulsigen®-D, or Quil-A® induced a low and IgG1-shifted antibody response and failed to protect vaccinated piglets against a homologous challenge. In conclusion, the type of adjuvant used in the vaccine formulation significantly influenced the immune response and efficacy of the vaccine against a homologous challenge.
Highlights
Streptococcus suis is a Gram-positive bacterium with 29 serotypes described based on the immunogenicity of its capsular polysaccharide (CPS) [1]
Survival rates and clinical signs The goal of our study was to compare the immunogenicity and protection of bacterin vaccines formulated with 6 different commercial adjuvants: an aluminum hydroxide gel (Alhydrogel®); an oil-in-water (O/W)/ nanoparticle dual adjuvant emulsion (Emulsigen®-D); a saponin (QuilA®); a water-in-oil-in-water (W/O/W) mineral oil-based adjuvant emulsion (MontanideTM ISA 206 VG); a waterin-oil (W/O) mineral oil-based adjuvant emulsion (MontanideTM ISA 61 VG); and a W/O/W mineral oil-based adjuvant emulsion (MontanideTM ISA 201 ISA)
Adjuvants are key components of vaccine formulations and possess multiple properties able to increase the level of the vaccine-induced immunological response, reduce the number of doses, control the release of the antigen at the site of the injection and, importantly, to modulate the type of induced immunity. The latter effect may have a major impact on the vaccine-induced protection against clinical disease [19]. Facing both the lack of effective commercial vaccines and the forthcoming restrictions in the prophylactic and metaphylactic use of antimicrobials, swine producers have increased the use of autogenous vaccines to prevent and control S. suis outbreaks
Summary
Streptococcus suis is a Gram-positive bacterium with 29 serotypes described based on the immunogenicity of its capsular polysaccharide (CPS) [1]. It causes disease in Obradovic et al Vet Res (2021) 52:133 and septic shock, with high importance in certain Asian countries where raw pig products are traditionally consumed [7, 8]. A recent field study showed that vaccination of piglets with a licensed autogenous vaccine composed of S. suis serotype 7 strain adjuvanted with oil-in-water adjuvant (confidential formulation) failed to induce an active immune response and clinical protection after vaccination of piglets [13]. Despite the importance of adjuvants, few studies have compared the effect of different adjuvants in the same experimental trial or at least under the same conditions [14, 15]
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