Vaccination-challenge interval markedly influences protection provided by Rispens CVI988 vaccine against very virulent Marek's disease virus challenge

Abstract

The Rispens (CVI988) vaccine is widely used to vaccinate chickens worldwide. We tested the protective effects of the Rispens vaccine against challenge with very virulent Marek's disease virus (vvMDV) at various intervals at, before or after vaccination. The experiment used commercial ISA Brown layers and vvMDV isolate 02LAR. The protective index (PI) was measured for vaccination challenge intervals (VCI) of -10, -5, 0, 5 and 10 days, with the negative values indicating challenge prior to vaccination. Chickens were challenged by injection with 400 plaque-forming units (PFU) of 02LAR and/or vaccinated with 3200 PFU of the Rispens vaccine virus at days 0, 5 and 10 of age, with appropriate negative controls injected with diluent only. The presence of visible Marek's disease tumours was assessed up to 56 days post challenge. MDV challenge in unvaccinated chickens resulted in tumours in 52% of chickens. The Rispens vaccine provided no significant protection when challenge preceded vaccination, with PIs of -4 and 21% for VCI of -5 and -10 days respectively. On the other hand, it provided PIs of 60, 85 and 100% at VCI of 0, 5 and 10 days respectively. The study also revealed that the vvMDV load in peripheral blood lymphocytes or feather tips at 14 and 21 days post infection as determined by quantitative real-time polymerase chain reaction, which can distinguish pathogenic MDV from the Rispens vaccine strain, was an accurate early predictor of Marek's disease incidence at 56 days post challenge. The load of Rispens virus in peripheral blood lymphocytes or feathers at the same times post vaccination did not offer similar predictive power.

Replication kinetics and shedding of very virulent Marek's disease virus and vaccinal Rispens/CVI988 virus during single and mixed infections varying in order and interval between infections

“…c) Patterns of viral load in feather cells more closely resembled those in PBL than those in dust suggesting that they are measuring virus of at least partially different origin. This study expands our understanding of the interaction between pathogenic and vaccinal viruses following vaccination with imperfect vaccines and together with the companion paper (Islam et al, 2013b) has implications for selection of appropriate samples to test for vaccination success.…”

“…UNE 10/ 057). Data on mortality, MD incidence and vaccinal protection are reported separately (Islam et al, 2013b).…”

“…The protection aspects of this experiment have been reported separately (Islam et al, 2013b) while here we present the viral kinetics aspects which tested the following hypotheses:…”

Detection of specific UL49 sequences of Marek's disease virus CVI988/Rispens strain using loop-mediated isothermal amplification

“…Currently, the most frequently used vaccines against MD are based on non-pathogenic FC126 strain of HVT and SB-1 strain belonging to the serotype 2, respectively (Schat, 1978;Witter, 1982). However, the highest protection is achieved after application of CVI988/Rispens-based vaccines (Witter, 1997;Islam et al, 2013). Moreover, it is also important to monitor the vaccine administration due to the high vulnerability of cell-associated vaccine viruses, once thawed.…”

Protection provided by Rispens CVI988 vaccine against Marek's disease virus isolates of different pathotypes and early prediction of vaccine take and MD outcome

“…Therefore, caution should be exercised when extrapolating to the field situation from studies in experimental chicken strains or birds not having mab directed against MDV, as is generally the case with specific pathogen-free (SPF) chickens. Rispens vaccine protection studies have mostly used mab −ve chickens (Buscaglia et al, 2004;Gong et al, 2014;Zhang et al, 2015) or these and mab + ve chickens of experimental strains (Witter et al, 1995(Witter et al, , 2005 while only a few recent studies have used commercial mab + ve chickens (Lee et al, 2010(Lee et al, , 2013Islam et al, 2013;Chang et al, 2014). In the present study we used commercial chickens of one of the major laying strains worldwide.…”