Effects of infectious bursal disease virus and reticuloendotheliosis virus infection of chickens on the incidence of Marek's disease and on local tumour development of the non-producer JMV transplant.

Dual infection of chickens with the HPRS-16 or HPRS-B14 strains of Marek's disease (MD) virus and non-transforming reticuloendotheliosis virus (REV-C) was shown not to affect significantly the incidence of MD or the incidence of MD lymphomas. Simultaneous infection of chickens with a pathogenic strain of infectious bursal disease virus (IBDV) and the HPRS-B 14 strain of MD virus resulted in a consistently reduced incidence of MD and lengthening of the latent period, but the incidence of MD lymphomas was unaffected. Unmixed IBDV infection did not have any effect on the oncogenicity of the JMV non-producer MD tumour transplant or its attenuated variant JMV-A. In dually pre-infected chickens the JMV tumour development at the site of transplantation as stimulated by MD virus-induced immunosuppression was enhanced by IBDV infection. This phenomenon was attributed to an additive effect of MDV- and IBDV-induced immunosuppression.