Abstract
Poultry salmonellosis causes serious economic damage and must be prevented by disinfection, zoohygienic measures or by vaccination. To develop a new polyvalent vaccine against poultry salmonellosis, we used bacterial strains of Salmonella enteritidis, S. typhimurium and S. gallinarum. Antigenic and immunogenic efficacy of the vaccine was tested on specific-pathogen free chickens, which were divided into five groups of 10 birds in each group and were vaccinated intramuscularly at 8 and 12 weeks: group A (non-immunized control), group B (S. enteritidis mono-vaccine), group C (S. typhimurium mono-vaccine), group D (S. gallinarum mono-vaccine) and group E (trivalent vaccine Polimun Salmo). None of the immunized birds showed such adverse reactions as abnormal behaviour, mortality or signs of anorexia, depression or diarrhea. Two weeks after the revaccination, 5 birds in each group were challenged by watering 3 cm3 of working suspensions of S. gallinarum, S. typhimurium and S. enteritidis control strains at a concentration of 1 × 109 CFU. 72 h after the challenge, faeces were collected from all chickens in each group to identify Salmonella excretion with faeces, and the chickens were euthanized. Significant protection against the virulent challenge was observed in all immunized groups based on mortality and post-mortem lesions compared with the non-immunized control group. Blood samples were selected weekly from 5 chickens of each group for 184 days. The antigenic efficacy of the vaccines was studied by reaction of haemagglutination in the obtained serum. The potent antigen-specific response to lymphocyte activation found in all immunized groups indicated the induction of immune responses. Overall, the results showed that persistent immunity is formed in 4 weeks after the revaccination and lasts for a productive period. Immune response of chickens on day 184 after vaccination with Polimun Salmo was 1: 647, indicating that the developed polyvalent vaccine against common serovars of S. enterica in poultry is effective and immunogenic and can be further used in field studies.
Highlights
Poultry salmonellosis is a common disease caused by bacteria of the genus Salmonella
The study of culture and enzymatic properties of the isolated strains showed that all three strains of S. gallinarum ST-15, S. typhimurium and S. enteritidis on MPA medium grew in the form of rounded colonies of greyish colour with a blue tinge, which is typical for bacteria of the Salmonella genus
It was found that the strain S. typhimurium ST-15 gave a positive reaction with O-sera - receptors: 1, 4, 5 and 12; with H-sera - receptors: i – 1-phase; 1.2 – 2-phase), which is characteristic of S. typhimurium bacteria
Summary
Poultry salmonellosis is a common disease caused by bacteria of the genus Salmonella. Due to the persistence of the bacteria in the environment and the rapid development of antibiotic resistance, the problem of human and animal diseases with salmonellosis has remained relevant during the last ten years. As of August 2019, Centers for Disease Control and Prevention (USA) has registered 1003 people infected with Salmonella outbreak strains in 49 states, of which 23% were children under the age of 5. Epidemiologic and laboratory records indicate that contact with backyard poultry, such as chicks and ducklings, from multiple hatcheries were the likely source of these outbreaks (Centers for Disease Control and Prevention, 2019). The main source of this disease for humans is the meat of chickens, turkeys and pigs, as well as chicken eggs (Borges et al, 2017; Cheng et al, 2019)
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