EFFECTS OF POLYCHLORINATED-BIPHENYLS ON THE INFECTION OF CHICKENS WITH NONONCOGENIC MAREKS-DISEASE VIRUS-STRAINS

The report describes the effects of polychlorinated biphenyls (PCB) on Brown Leghorn chickens infected with non-oncogenic strains (M and K) of Marek's disease virus (MDV) and observed during a 5-week period. Tw o groups of chicks were each infected with MDV isolates M and K, respe ctively, in doses of 10(3) PFU per bird and fed a non-contaminated fee d mixture. Two other groups were infected in the same way and fed the same feed mixture contaminated with PCB at 50 mg per kg feed. Non-infe cted chickens fed the non-contaminated feed mixture were used as contr ols. At weekly intervals the birds were subjected to serological exami nation and weighed and their lymphoid organs, skin, nerves and gonads were examined histopathologically. PCB produced apathy, a reduction in body mass, moulting disorders and white discolouration of the feather s. They reduced the production of active MD-precipitating antibody and the incidence of microscopic MD-lymphoproliferative lesions, as compa red with the data obtained in the birds only infected. They potentiate d cytolytic changes in the lymphoid organs and, at the end of the expe riment, caused atrophy of the bursa of Fabricius and of the thymus. Mo rphological signs of local cell-mediated immunity in the lymphoid orga ns were observed very rarely. The results are helpful to the different iation of morphological immunosuppressive changes of different etiolog y and contribute to a better understanding of the causes of reduced im munological competence in poultry.