Characterization of very virulent Marek's disease viruses isolated in Japan |
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Authors: | K Imai N Yuasa H Iwakiri K Nakamura H Hihara T Ishita A Inamoto I Okamoto K Ohta M Maeda |
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Affiliation: | Poultry Disease Laboratory, National Institute of Animal Health, Seki, Gifu, Japan. |
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Abstract: | Pathogenicity of two isolates of Marek's disease virus (MDV), MS1 and MS2, from chickens was examined in two genetically different strains of chickens, MD-susceptible P-2 chickens and less susceptible PDL-1 chickens. The isolates induced an early mortality syndrome unassociated with lymphoproliferative lesions in P-2 chickens. There were no significant differences in pathogenicity between our isolates and the Md/5 strain of very virulent MDV (vvMDV) in both P-2 and PDL-1 chickens. Protective indices of turkey herpes virus (HVT) vaccine against challenge with MS1 or MS2 in P-2 chickens were 54% and 28%, respectively, whereas HVT gave more than 80% protection in PDL-1 chickens. These results indicate that the two isolates could be classified as vvMDV. In contrast, a bivalent vaccine composed of HVT and serotype 2 MDV, and CVI988 vaccine gave good protection against challenge with the isolates in P-2 chickens; however, the best protection was given by the CBI988 vaccine. This is the first report of isolation of vvMDV in Japan. |
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