Standardization of a model to study revaccination against Marek's disease under laboratory conditions

Abstract

Revaccination, the practice of administering Marek's disease (MD) vaccine a second time, has been used in commercial poultry flocks for many years. The rationale is largely anecdotal as the few published reports have failed to provide support for the value of the practice. In the present work, we have standardized a model to study MD revaccination under laboratory conditions. Nine bird experiments were conducted to evaluate homologous revaccination (same vaccine administered twice) and heterologous revaccination (administration of two different vaccines) with various challenge models. Our results demonstrated that heterologous revaccination (with a second vaccine more protective than the first vaccine) but not homologous revaccination provided a beneficial increase in protection. Administration of the first vaccine at 18 days of embryonation followed by a more protective second vaccine at hatch reproduced systematically the benefits of revaccination. In addition, our results show that revaccination protocols might aid in solving major drawbacks associated with various highly protective experimental MD vaccines; that is, lymphoid organ atrophy and residual virulence. Strain RM1 is one of the most protective vaccines against early challenge with highly virulent MD virus but it induces severe lymphoid atrophy in chickens lacking maternal antibodies against MD virus. In this study, strain RM1 did not induce lymphoid organ atrophy when administered as second vaccine in a revaccination protocol. Similarly, strain 648A100/BP5 maintains residual virulence in chickens lacking maternal antibodies against MD virus but did not induce any lesions when used as a second vaccine. Until now, arbitrary revaccination protocols have been occasionally proven useful to the poultry industry. The model developed in this study will allow for a better understanding of this phenomenon and its optimization. A more rational use of this practice will be of great help to control MD outbreaks until better vaccines are available.

Marek’s Disease and Differential Diagnosis with Other Tumor Viral Diseases of Poultry

“…Synergism is strongly serotype-specific and is especially evident between combinations of serotypes 2 and 3 (Witter, 1992). Her results indicate that the benefit of double vaccination can be achieved by using a less efficient first vaccine followed by a more efficient second vaccine (Gimeno et al, 2011b). However, augmentation of protection for MD vaccines has been observed with two additional systems.…”

“…No protective synergism has been reported between combinations of serotype 1 with serotypes 2 or 3. In ovo vaccination followed by a second vaccination at the day of age seems to be the most beneficial protocol (Gimeno et al, 2011b). Combinations of HVT and glutaraldehyde-inactivated serotype 1 MDV obtained from feather follicles was reported to improve protection (Pruthi et al, 1987).…”

Evaluation of Factors That Influence Dose Variability of Marek's Disease Vaccines

“…The only case for this practice was to protect chicks that had been erroneously missed during the initial vaccination. Recently, however, revaccination was shown to increase protection against early challenge [206][207][208]. It resulted in two replication phases of vaccine viruses and a lower replication phase of the challenge virus [208].…”

“…It resulted in two replication phases of vaccine viruses and a lower replication phase of the challenge virus [208]. It has also been shown that for revaccination to succeed, the second vaccine administered should inherently be more protective than the first (ex: HVT first, CVI-988 second) and both vaccines should be administered before challenge [207]. The recommended protocol is to administered both vaccines prior to MDV challenge, the first in ovo at 18ED and the second subcutaneously at hatch [206].…”