Pathological Lesions of Chicken Organs After Infection with Turkey Herpesvirus Thv-Bio-I

Veterinarni Medicina 37, 1992, 463-470

The objective of our work was to investigate the dynamics of pathological lesions of chicken organs after infection with high doses of turkey herpesvirus THV-BIO-I. This virus strain is commonly used in form of the Marvak vaccine against Marek's disease of poultry in Czechoslovakia. High doses of the vaccine are used in practice with respect to the epizootological situation. The incidence of pathological lesions in the organs of Brown Leghorn chickens was investigated in a five-week experiment. One-day chickens were infected intramuscularly with the HVT strain at the doses of approximately 10(2), 10(3) and 10(4) PFU in 0.2 ml of infective inoculum per chick. The body weights of ten chickens of each group were recorded at intervals of 1, 2, 3 and 5 weeks after infection, serological examination was performed for precipitating antibodies to MDV and the feather was examined for MDV-antigen. Bursae Fabricii and spleens were weighed. Thymus, bursae Fabricii, spleens, peripheral nerves (n. ischiadicus and pl. brachialis) and gonads were sampled for histopathological examination. Neither maternal nor post-infection antibodies were found in any chick. Cytolytic lesion severity of lymphoid organs was scored using the scale of immunosuppression degrees (0-4). Morphological criteria were published in a previous paper (Halouzka and Jurajda , 1991b). The differences observed in the weights of bursa Fabricii and spleen between the infected and control chickens were not statistically significant. The observed lymphoid infiltrations in the skin, gonads, nerves and other tissues following the HVT infection are well-known and correlate with the infection dose. The cytolytic lesions in the bursa Fabricii and thymus are not however mentioned in the literature. Lesions observed in our work were mild and disappeared within three weeks after infection. They correlated positively with the infection dose. Our results demonstrated that the otherwise apathogenic HVT administered at high doses induced mild, transient regressive lesions of lymphoid organs in sensitive chickens, which could have practical consequences. Sporadicaly observed syncytial ''Hassall corpuscle-like'' formations represent a nonspecific immune reaction to antigen stimulation and peripheral function of bursa Fabricii. The observed degeneration of peripheral nerve neuraxons is one of the manifestations of axon dystrophic lesions and corresponds to neurophilament and neurotubule destruction. The interpretation of pathogenesis of these lesions is difficult according to our methods, but in comparison with similar lesions in various pathological processes we consider it as an immunopathological process. In our experiment high doses of the Marvak vaccine caused mild regressive lesions of lymphoid organs and appearance of lymphoid infiltrations in the early phases of infection. Pathological lesions were severest at the highest infection doses. We do not take them for MD-specific lesions

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