Influence of vaccine deposition site on post-vaccinal viraemia and vaccine efficacy in broiler chickens following in ovo vaccination against Marek's disease

Abstract

In ovo vaccination against Marek's disease is a widely used technology in the broiler industry. A series of experiments was carried out to determine the site of vaccine deposition in the egg during automated in ovo vaccination, and the effect of vaccine deposition site and dose on vaccine responses following vaccination with cell-associated herpesvirus of turkeys in commercial broiler chickens. Vaccine deposition site following automated in ovo vaccination was principally influenced by the age of embryo, with egg size having a smaller effect. The frequency of vaccine deposition inside the embryo body increased as incubation progressed from day 17.5 to 19.5. In experiments using manual vaccine deposition intra-embryonically (IE) or extra-embryonically (EE) at day 18.5, EE vaccine deposition resulted in a significantly delayed development of post-vaccinal viraemia relative to both IE vaccination and subcutaneous vaccination at hatch. There were no effects of vaccine dose (2000, 4000 or 8000 plaque forming units) on the timing of post-vaccinal viraemia. The timing of post-vaccinal viraemia was found to be a good indicator of the level of protection provided by the vaccine against challenge with earlier viraemia associated with better protection. IE vaccine deposition induced significantly greater protection than EE deposition against challenge with a virulent strain of Marek's disease virus. IE deposition consistently produced a high level of protection (68 to 84%) irrespective of vaccine dose or challenge day, while EE vaccine deposition produced no or low levels of protection (0 to 27%) depending on the vaccine dose and day of challenge. The growth of challenged chickens was also affected by site of vaccine deposition, with significantly higher live weights at day 56 of age in IE compared with EE vaccinated groups. These data suggest that the site of vaccine deposition within the embryo is an important determinant of the success of in ovo vaccination.

Immunosuppressive effects of Marek's disease virus (MDV) and herpesvirus of turkeys (HVT) in broiler chickens and the protective effect of HVT vaccination against MDV challenge

“…First, LW reduction in this study was observed from day 28 onwards, but has been reported by day 7 in SPF chickens (Witter et al, 1980). Second, the onset of first MDV-related mortality occurred at days 33 to 35 post-challenge in our other experiments using the same virus and chickens as these experiments (Islam et al, 2001a), but has been reported as early as days 7 to 16 post-challenge in other studies (Witter et al, 1980(Witter et al, , 1999. Whether this delay in pathogenesis is due to the maternal antibody in our birds, their difference in genotype, or a combination of these cannot be resolved from these studies.…”

Pathotyping of Australian isolates of Marek's disease virus and association of pathogenicity withmeqgene polymorphism

“…Although it was highly pathogenic in unvaccinated chickens, inducing MD lesions in 84% of at-risk unvaccinated chickens, vaccination with HVT provided complete protection against these lesions. We have observed complete protection with HVT previously with this strain in commercial broilers, although protection of 70 to 80% is more typical (Islam et al, 2001(Islam et al, , 2008. Given these findings, the provisional virulence ranking of very virulent ascribed to this virus by De Laney et al (1998) cannot be supported.…”

Kinetics of Marek's disease virus (MDV) infection in broiler chickens 1: effect of varying vaccination to challenge interval on vaccinal protection and load of MDV and herpesvirus of turkey in the spleen and feather dander over time

“…The VCI is an important determinant of efficacy for all live viral vaccines (Alexander et al, 2006) as longer intervals enable more time for vaccinal virus replication and the mounting of an effective adaptive immune response. HVT has been used as a vaccine against MD in broiler chickens since 1971, and since the early 1990s it has been increasingly administered in ovo 3 to 4 days before hatch using automated egg handling and injecting systems (Sharma & Burmester, 1982;Ricks et al, 1999;Islam et al, 2001). Part of the rationale for in ovo vaccination is to provide additional time for the development of an effective immune response before challenge, which is commonly assumed to be early in the life of the chicken.…”