Further characterisation of the CVI 988 strain of Marek's disease virus

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Abstract
The CVI 988 strain of Marek's disease virus (MDV) has been studied for markers in vitro and in vivo. It was shown by indirect immunofluorescence assays that this strain belonged to the HPRS‐16 serotype of MD viruses. The virus was positive for precipitating ‘A’ antigen. Medium plaques were produced in cell cultures. Therefore the CVI 988 strain could not be distinguished in vitro from other virus strains of the same serotype. The CVI 988 strain proved to be pathogenic for genetically susceptible Rhode Island Red chickens if inoculated at high doses equivalent to 10 times the field dose of the vaccine. The virus caused symptoms of classical Marek's disease in up to 28.5% of the inoculated chickens with gross lesions restricted to the peripheral nerves. Visceral tumours never occurred. The virus spread to uninoculated control chickens housed in the same pen. The CVI 988 strain can be classified as a mildly pathogenic classical Marek's disease virus of the HPRS‐16 serotype.