title: Characterization of very virulent Marek's disease viruses isolated in Japan.
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.
authors.affiliation: Poultry Disease Laboratory, National Institute of Animal Health, Seki, Gifu, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Imai
authors.forename: N
authors.initials: N
authors.lastname: Yuasa
authors.forename: H
authors.initials: H
authors.lastname: Iwakiri
authors.forename: K
authors.initials: K
authors.lastname: Nakamura
authors.forename: H
authors.initials: H
authors.lastname: Hihara
authors.forename: T
authors.initials: T
authors.lastname: Ishita
authors.forename: A
authors.initials: A
authors.lastname: Inamoto
authors.forename: I
authors.initials: I
authors.lastname: Okamoto
authors.forename: K
authors.initials: K
authors.lastname: Ohta
authors.forename: M
authors.initials: M
authors.lastname: Maeda