Abstract
ABSTRACT Salmonella Heidelberg (SH) has represented a great concern to the Brazilian poultry industry in the last years. It is known that immunosuppression in poultry is a contributing factor to increase Salmonella faecal shedding and to disturb control programmes. Not only infectious bursal disease (IBD) virus but also some live vaccines have been reported to induce immunosuppression. In the present study we assessed the effects of two live vaccines against IBD on SH-infected broiler chicks. At 7 days of age, birds of three groups (vaccinated with recombinant HVT-IBD vector, with immune complex-IBD vaccine and unvaccinated) were orally challenged with 1 x 108 CFU of SH. A group of hatchmates remained unvaccinated/unchallenged to serve as negative controls. Caecal colonization and systemic invasion were evaluated by bacterial enumeration at 1, 3, 5, 7 and 14 days post-infection (Dpi) and SH faecal shedding assessed by cloacal swabs at 3, 7, 10 and 14 Dpi. The counts of SH in caecal contents were higher in birds vaccinated with immune complex-IBD than in those that received the HVT-IBD vector vaccine at 5, 7 and 14 dpi (p<0.01). There were no statistical differences in bacterial counts in liver and spleen among birds of different groups. Cloacal swabs also indicated that the birds vaccinated with immune complex-IBD shed more SH than those vaccinated with HVT-IBD vector or those unvaccinated (p<0.01). The results of the present study suggested that the immunosuppressive effect of the immune complex-IBD vaccine helped to increase the SH-faecal shedding in the infected birds.
Highlights
Millions of cases of human foodborne diseases worldwide are caused by Salmonella (WHO, 2018)
Immunosuppressive agents that favour Salmonella shedding and the environmental contamination may affect the effectiveness of control programmes
Of the Bursa of Fabricius (BF) in birds vaccinated with an immune complex-infectious bursal disease (IBD) vaccine, whereas birds that received HVT-IBD vector vaccine showed preserved BF tissue
Summary
Millions of cases of human foodborne diseases worldwide are caused by Salmonella (WHO, 2018). Salmonella serotype Heidelberg (SH) is amongst the most prevalent serotypes isolated from human and non-human sources (CDC, 2018). In Brazil, SH represented about 56% of all Salmonella isolates recovered from broiler carcass in 2017 ( Brasil, 2018). In order to reduce the levels of contamination of poultry products, actions need to be taken at the whole poultry production chain (Gast, 2013). In this context, factors that favor horizontal or vertical transmission of Salmonella at farm level are detrimental to any control programme ( Koutsoumanis et al, 2019)
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