A comparison of the effects on the humoral and cell-mediated Immunity between an HVT-IBD vector vaccine and an IBDV-immune complex vaccine after in ovo vaccination of commercial broilers
Silke Rautenschlein, Stéphane Lemiere Birgid Simon and Francesco Prandini
Infectious bursal disease virus (IBDV), a member of the Birnaviridae family, cause an acute, highly contagious and immunosuppressive disease in young chickens (Eterradossi & Saif, 2008). The main target cells for IBDV replication are dividing B lymphocytes; thus infection leads to the destruction of lymphoid cells in the bursa of Fabricius and, to a lesser degree, in other lymphoid organs. The acute phase lasts one to two weeks and is often accompanied by variable mortality. In birds that survive and control IBDV infection depleted bursal follicles become repopulated with B cells and immune competence may return to normal levels after some time (Kim et al. , 1999; Withers et al. , 2006; Withers et al. , 2005). Replication of IBDV in the bursa is accompanied by an influx of activated T cells that control viral replication but also delay recovery of infected animals (Kim et al. , 2000; Rautenschlein et al. , 2002; Tanimura & Sharma, 1997). Systemically T cell immunity may be also compromised as indicated by a suppressed mitogenic response, which is mediated by soluble factors released by IBDV-activated macrophages (Kim et al. , 1998). A variety of vaccines are commercially or experimentally available to protect chickens against IBDV (Haygreen et al. , 2006; Hsieh et al. , 2010; Ivan et al. , 2005; Lemiere et al. , 2011; Omar et al. , 2006; Perozo et al. , 2009; Rautenschlein et al. , 2005; Wang et al. , 2007). Attenuated IBD-live vaccines and IBD-immune complex (Icx) vaccines may have the disadvantage of transient destruction of bursa follicles and residual immunosuppressive abilities (Corley & Giambrone, 2002; Rautenschlein et al. , 2005). Furthermore, maternal antibodies may interfere with the replication of the IBDV vaccine strain delaying the onset of protection (Block et al. , 2007). IBD-immune complex vaccines are designed to by-pass the neutralizing activity of maternal antibodies (Ivan et al. , 2005; Jeurissen et al. , 1998). In maternal antibody negative birds IBD-Icx vaccines were also shown to have residual immunosuppressive abilities (Corley & Giambrone, 2002). New generation vaccines such as recombinant herpes virus of turkeys (HVT) expressing immunodominant IBDV peptides such as VP2, which induces IBD-neutralizing antibodies, circumvent the problem of interference with IBD-maternal antibodies at the time of vaccination (Bublot et al. , 2007; Le Gros et al. , 2009; Lemiere et al. , 2011; Perozo et al. , 2009; von Bulow & Klasen, 1983). It is also speculated that this HVT does not induce significant immunosuppression (Islam et al. , 2002; Reddy et al. , 1996), but this aspect has not been investigated for HVT expression vectors in combination with inserts of different viruses.
Our objective was to compare under experimental conditions the effects of an HVT-IBD vector vaccine with a live IBD immune complex vaccine (Icx-IBD) on the immune system and the induction of immune responses in commercial broilers.
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