History of the First-Generation Marek's Disease Vaccines: The Science and Little-Known Facts.

Shortly after the isolation of Marek's disease (MD) herpesvirus (MDV) in the late 1960s vaccines were developed in England, the United States, and The Netherlands. Biggs and associates at the Houghton Poultry Research Station (HPRS) in England attenuated HPRS-16, the first cell-culture-isolated MDV strain, by passaging HPRS-16 in chick kidney cells. Although HPRS-16/Att was the first commercially available vaccine, it never became widely used and was soon replaced by the FC126 strain of herpesvirus of turkeys (HVT) vaccine developed by Witter and associates at the Regional Poultry Research Laboratory (now Avian Disease and Oncology Laboratory [ADOL]) in East Lansing, MI. Ironically, Kawamura et al. isolated a herpesvirus from kidney cell cultures from turkeys in 1969 but never realized its potential as a vaccine against MD. Rispens of the Central Veterinary Institute (CVI) developed the third vaccine. His associate, Maas, had found commercial flocks of chickens with MDV antibodies but without MD. Subsequently, Rispens isolated a very low pathogenic strain from hen number 988 from his MD antibody-positive flock, which was free of avian leukosis virus and clinical MD. This isolate became the CVI-988 vaccine used mostly in The Netherlands. During the late 1970s, HVT was no longer fully protective against some new emerging field strains. The addition of SB-1, isolated by Schat and Calnek, to HVT improved protection against the emerging very virulent strains. In the 1990s CVI-988 became the worldwide vaccine gold standard. This review will present data from published papers and personal communications providing additional information about the exciting 15-yr period after the isolation of MDV to the development of the different vaccines.