Key result
Marek's disease strain CVI-988 vaccine caused paralysis and neuritis in 88% of susceptible chickens, whereas five plaque-purified preparations caused no lesions.
Absolute Event Rate: 88% vs 5.1%
Plaque-purified preparations of Marek's disease virus strain CVI-988 showed reduced pathogenicity compared to the commercial vaccine strain in susceptible chickens.
May inform safer Marek's disease vaccine development; leaves open validation in commercial poultry.
The pathogenicity of Marek's disease (MD) strain CVI-988 vaccine, eight plaque-purified preparations originating from this strain, and the vaccine HVT FC126 (based on herpesvirus of turkeys) was determined by intramuscular administration of high virus doses to day-old specific-pathogen-free Rhode Island Red (RIR) chickens, which are extremely MD-susceptible. Paralysis and neuritis were observed in 88% of RIR chickens inoculated with MDV CVI-988 at the cell-passage level of the commercial vaccine. HVT FC126 caused paralysis in two of 39 RIR chickens tested, of which one had an endoneural lymphoma, and another three had endoneural inflammation. Five plaque-purified MDV CVI-988 virus preparations at various cell-culture-passage levels caused no lesions. Of another three clones, two caused inflammatory B-type lesions in the nerves of 1/10 chickens, and the third clone caused inflammatory nonneoplastic MD lesions in the liver of 1/11 chickens.
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Pol et al. (1986) studied Marek's disease. Marek's disease strain CVI-988 vaccine and plaque-purified preparations vs. HVT FC126 vaccine was evaluated on Paralysis and neuritis. Marek's disease strain CVI-988 vaccine caused paralysis and neuritis in 88% of susceptible chickens, whereas five plaque-purified preparations caused no lesions.
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