Streptococcus suis: o impacto da variação antigênica na eficácia das vacinas autógenas
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| Main Author: | |
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| Publication Date: | 2024 |
| Format: | Master thesis |
| Language: | por |
| Source: | Repositório Institucional da UPF |
| Download full: | https://repositorio.upf.br/handle/123456789/10042 |
Summary: | Streptococcus suis is a Gram-positive, antigenically complex bacterium that can be classified into 29 different serotypes according to the variability of its polysaccharide capsule. It is the etiological agent of porcine streptococcosis, an acute systemic inflammatory disease that affects young piglets during the nursery phase and is characterized by arthritis, meningitis, polyserositis, endocarditis, septicemia, and sudden death. The development of porcine streptococcosis depends on the virulence of the circulating clinical strains of S. suis and the general health conditions of the herd. Currently, S. suis is the main cause of mortality and economic losses in the nursery phase of the Brazilian pig farming. S. suis serotype 9 is the most prevalent in Brazil, a situation also observed in European countries such as Spain and Netherlands. Control of this agent is complex and can be achieved by combining rigorous management practices with the use of vaccines, especially autogenous vaccines. Autogenous vaccines represent the main biological alternative against this agent. A fundamental aspect for the success of an autogenous vaccine is the assertive inclusion of microorganisms that are alone and/or in association causing disease in animals. In this work, we evaluated the immunogenicity and clinical efficacy of an autogenous vaccine based on three antigenically different clinical strains of S. suis serotype 9. The study was conducted on a commercial pig farm located in the western part of the state of Santa Catarina between June and November 2023. The first stage of the study consisted of the isolation and molecular characterization of clinical strains of S. suis isolated from outbreaks of S. suis-associated disease throughout the first half of 2023. Subsequently, the antigenic characteristics of the isolated S. suis serotype 9 strains were evaluated using the Smart Antigenicity Test platform, recently developed by AFK Imunotech. Subsequently, an autogenous vaccine was formulated by Vaxxinova, and the product was then evaluated in 3 sequential clinical experiments. In the first two experiments, the potency and efficacy of the vaccine were evaluated in two groups consisting of 174 and 201 piglets, respectively. In the third experiment, the vaccine was evaluated in pregnant sows and in piglets born from immunized dams. For this purpose, 18 sows were immunized intramuscularly at 65 and 86 days of gestation. Piglets born from these sows (n=273) were immunized intramuscularly at 21 and 35 days of age. In the first two studies, blood samples were collected at 21, 35, 42, 49 and 63 days of age. In the third study, in addition to the aforementioned time points, samples were also collected on the 7th and 14th day of life. Blood samples were collected from sows at 65, 86, 100 and 107 days of gestation. Colostrum samples were collected at farrowing. Vaccine efficacy was assessed by comparing the mortality rate in the farm nursery before and after the introduction of the new vaccine. Antibody titers were determined by indirect ELISA based on the vaccine strain AFK 168/22. Our results demonstrated the circulation of strains with 3 different antigenic profiles on the farm studied. We also observed that strains with the same xv virulence profile presented different antigenic profiles, and vice versa. The autogenous vaccine, based on 3 clinical strains of S. suis representative of the identified antigenic clusters, was immunogenic in the three clinical experiments performed. The onset of immunity induced by vaccination was defined based on serology and mitigation of death as being 7 days after revaccination. The vaccine was equally immunogenic in sows, ensuring the production of colostrum with high IgG titers (Log10 = 4.19 0.43). The duration of immunity in 100% of piglets was estimated to be of 3 weeks. Regarding clinical protection, the combination of immunization of sows and piglets at weaning reduced the mortality rate from 5.52% (experiment 1), 5.31% (experiment 2) to 2.56% (experiment 3). Finally, we compared the performance of the trivalent vaccine (formulated in this study) with that provided by the monovalent vaccine, formulated by the same commercial laboratory, and used during the five months of 2023. Our results demonstrated that the trivalent vaccine progressively reduced nursery mortalities on the farm from the first month of use (June), reaching its maximum performance (mortality of 1.76%) in November. Our results demonstrate, for the first time, the application of the Smart Antigenicity Test platform to select clinical vaccine strains to formulate smart autogenous vaccines capable of controlling the development of diseases caused by S. suis serotype 9. |
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