Immunogenicity and duration of immunity of the polyvalent vaccine against chicken salmonellosis

Immunogenicity and duration of immunity of the polyvalent vaccine against chicken salmonellosis

Full-Text PDF

Poultry salmonellosis is a common disease caused by bacteria of the genus Salmonella. The economic impact of the infection cannot be overlooked, as it inflicts serious economic damage on both the private sector and the economy of the state as a whole. 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. Despite the detailed study of salmonellosis pathogens, the definitive elimination of this disease is impossible. Also one of the factors in the problem of salmonellosis in the world is the transmission of the pathogen from sick birds to humans.

The United States Department of Agriculture estimates the economic damage caused by foodborne infections is $3.13 billion a year. The share of economic damage directly caused by salmonellosis is $2.56 billion a year. A European outbreak of salmonellosis occurred in 2008 in the European Union. Salmonellosis ranked second after campylobacteriosis that year. From the entire list of Salmonella isolated during that period, the serovars of S.enteritidis and S.eyphimurium accounted for the largest share.

The situation in Ukraine is also pushing for an effective way to prevent poultry salmonellosis. According to researchers from the Veterinary Diagnostic Center in the period 2014–2017 139 isolates of Salmonellaspp. were isolated, 47 of which were in the Kyiv region.

The rapidly increasing number of antibiotic-resistant salmonella isolates found during research in food stresses the urgency of finding an effective way to prevent poultry salmonellosis. Isolates resistant to the beta-lactam antibiotics, fluorophenicols, aminoglycosides, tetracyclines, chloramphenicols have now been identified. The isolates found on the territory of Ukraine for the period of 2015–2017 are resistant to antibiotics such as flumequin, oxytetracycline, enrofloxacin, danofloxacin, tilmicosin. At the state level, the problem of poultry salmonellosis occupies an important place, since the decree No. 310 of 19.09.2016 by the Ministry of Agrarian Policy and Food of Ukraine approved the instruction on the prevention and elimination of poultry salmonellosis. It was found that in laying hens S enteritidis is most commonly found, in broilers – S. typhimurium, in ducks, geese, pigeons – S. typhimurium (On approval of the instructions for the prevention and elimination of avian salmonellosis. Order of the Ministry of Agrarian Policy and Food of Ukraine No. 310 dated 19.09.2016).

For the prevention of salmonellosis, in addition to antibiotic therapy, disinfection and improvement of the zoohygienic conditions of poultry, vaccines are used. Vaccination, especially on large farms, is an effective way to address human and avian salmonellosis. Immunization of chickens can reduce both horizontal and vertical transmission of salmonella pathogens. According to the analysis, vaccinated chickens have a lower prevalence of salmonella in the caecum (38.3% vs. 64.2%; P < 0.001) and genital system (14.2% vs. 51.7%; P < 0.001). A lower prevalence of Salmonella in broiler chickens (18.1% vs. 33.5%; P < 0.001) obtained from vaccinated livestock. Factors affecting the ability of Salmonella to infect particular birds, such as chickens, are complex and form the so-called “epizootic triangle” – susceptible animals, pathogens and external influences.

Most scientists agree that the major efforts to prevent salmonellosis should be directed to those serovars which pose the greatest danger to the bird and human body. These serovars for Europe are considered to be S. typhimurium and S. enteritidis, which have a wide range of susceptible organisms. S. enterica serovars such as S. typhi, S. dublin and S. gallinarum have a limited range in which they are associated with one or more animal species.

The range of registered vaccines against chicken salmonellosis on the Ukrainian market is represented by leading foreign manufacturers, and one domestic vaccine developed by the NEC “Institute for Experimental and Clinical Veterinary Medicine”.

Protection of poultry is due to the use of most inactivated vaccines, which are usually bivalent, containing as immunogens the serovars of S. typhimurium and S. enteritidis, protective determinants of S. enterica strain. Also registered are SalmAbic Plus, Israel, which additionally introduced the S. infantis serovar and the Cevac SalmuneE TEK, USA, with the additional S. kentucky serovar.

But available vaccines do not prevent typhoid (the main intracellular bacterial pathogen is the gram-negative bacterium S. enterica serovar gallinarum (S. gallinarum)) and septic disease of chickens, which is manifested in acute mortality, usually 60–70%, and inflammation, typhlitis and omphalitis, and leads to significant economic losses for poultry.

Therefore, there is a need for polyvalent vaccines that can be safely administered to chickens (especially at a young age) to obtain required immune reactions and adequate protection against salmonellosis. Vaccines against Salmonella can act by various mechanisms. Inactivated vaccines are widely accepted in many countries for the vaccination of commercial table-egg layers. Most inactivated vaccines contain antigens and adjuvants with different levels of protection. Тhe recent development of novel adjuvant technology is very promising for the development of totally safe, inactivated Salmonella vaccines capable of inducing potent immune stimulation targeting different weapons of the chickens’ immune system.

The objective of our research was to study the immunogenicity and duration of immunity of the developed inactivated vaccine Polimun Salmo by vaccinating specific pathogen free (SPF) chickens with monovalent vaccines, made from separate antigens, and multivalent vaccine, with subsequent challenge of vaccinated birds by virulent strains of Salmonella, and to study contamination of internal organs and formation of immunity response during 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 vacci- nation 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.

Full-Text PDF