Abstract
The Infectious Bursal Disease (IBD) is a contagious viral disease that affects young chickens and may cause high morbidity and mortality. As the virus is very resistant to the environment, vaccination is required in case of high infection pressure. Due to variations in the virulence degree of the vaccines available to control IBD, this study aimed at evaluating the pathogenicity and immunogenicity of three types of vaccines. In total, 220 one-day-old specific pathogen free (SPF) chickens were immunized with recombinant, immune-complex and intermediate vaccines, or not vaccinated (55 birds per group) and challenged with IBD G11 strain on day 25. On days 25, 30, and 35, the Bursa of Fabricius (BF) were submitted to gross and histological examination, and serum samples were submitted to ELISA to determined anti-IBD antibody titers. On day 23, chickens were submitted to the test of hypersensitivity to phytohemagglutinin to evaluate the immunosuppressive effect of vaccines on the cell-mediated immunity. The results have indicated that the immune-complex vaccine induced the most severe BF lesions, whereas the recombinant vaccine preserved BF tissue and cell integrity. The three evaluated vaccines induced humoral immunity of similar intensity. The cellular reaction to phytohemagglutinin of the chickens immunized with recombinant and immune-complex vaccines was less severe compared with the unvaccinated chickens. In conclusion, these results indicate that the immune-complex vaccine was the most pathogenic and that all vaccines were effective in protecting SPF chickens against IBD.
Highlights
The Infectious Bursal Disease (IBD) is a highly contagious acute viral infection, affecting young chickens (Eterradossi & Saif, 2008)
Previous studies have demonstrated that Infectious Bursal Disease Virus (IBDV) strains with different virulence may differ in their ability to replicate in vivo, to induce humoral immunity, and to cause immunosuppression
Thereby, this study aimed at characterizing the pathogenicity and immunogenicity of IBD vaccines currently utilized to control IBD in Brazil in specific pathogen free (SPF) chickens, as well as to determine the protection degree of chickens challenged with a highly-virulent strain of IBDV provided by those vaccines by analyzing their effect on the cell-mediated immunity of SPF birds
Summary
The Infectious Bursal Disease (IBD) is a highly contagious acute viral infection, affecting young chickens (Eterradossi & Saif, 2008). Infectious Bursal Disease Virus (IBDV), belonging to serotype 1, is an important immunosuppressive virus of chickens, hastropism for the Bursa of Fabricius (BF), and its intense viral replication may cause severe lymphocyte depletion in bursal follicles (Muller et al, 1979). The infection with IBDV may exacerbate previous infections with other infectious agents, and may reduce the capacity of the bird to respond to vaccination, as the virus damages the humoral and cellular immune responses of chickens (Sharma et al, 2000). Previous studies have demonstrated that IBDV strains with different virulence may differ in their ability to replicate in vivo, to induce humoral immunity, and to cause immunosuppression. The relative effectiveness of these strains to stimulate cell-mediated responses, and the relation of virulence with these responses, is not known yet (Rautenschlein et al, 2003).
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