Evaluation of the protective efficacy of <i>Salmonella</i> Gallinarum 9R strain vaccine against <i>Salmonella</i> strains isolated from cases suspected of salmonellosis outbreaks in poultry farms in central Ethiopia

Abstract

Salmonellosis is one of the most important bacterial diseases of poultry causing heavy economic losses. Though it can be prevented through vaccination, regular monitoring of the protective efficacy of the vaccine against field outbreaks is essential since antigenically dissimilar serovars may evolve compromising the efficacy of the vaccine. This study was, therefore, carried out to evaluate the protective efficacy of the currently used attenuated Salmonella Gallinarum 9R strain vaccine against experimental challenge with field isolates of Salmonella strains obtained from disease outbreaks. Three Salmonella serovars viz Salmonella Gallinarum, Salmonella Pullorum and Salmonella Enteritidis isolated and identified (phenotypically and molecularly) from outbreaks suspected of salmonellosis were used for the challenge experiment. A total of 90 chickens randomly divided into 2 categories (vaccinated and non-vaccinated control) each comprising 45 birds were used for protective efficacy study. Each of these categories were further subdivided and randomly assigned into 3 groups each comprising 15 birds for challenge with each of the three field Salmonella serovars. Chickens were vaccinated subcutaneously with live attenuated Salmonella Gallinarum 9R vaccine containing 2x107 CFU per dose. Each group in both vaccinated and non vaccinated category were challenged with the three field serovars (one strain per group) through oral administration of 1 ml of bacterial suspension containing 5×107organisms. Post challenge follow-up showed no mortality in all vaccinated groups challenged with each of the three serovars while a mortality of 53.3% (N=8), 13.3% (N=2) and 0% was observed in S. Gallinarum, S. Pullorum and S. Enteritidis challenged nonvaccinated groups, respectively. None of the challenge Salmonella strains were  recovered from liver and spleen of the vaccinated birds two weeks after challenge. In conclusion, the currently used attenuated S. Gallinarum 9R strain vaccine against fowl typhoid can effectively confer protection not only against field strains of Salmonella Gallinarum, but also cross-protection to S. Pullorum and S. Enteritidis involved in causing poultry salmonellosis outbreaks in Ethiopia.

Keywords: Central Ethiopia; Poultry; Salmonellosis; Vaccine efficacy