title: Late Marek's disease in adult chickens inoculated with virulent Marek's disease virus.
abstract: Recently, excessive losses from Marek's disease (MD) have been noted in adult laying flocks over the age of 40 weeks. We defined these late outbreaks in adult chickens as "late MD", and experimentally reproduced the disease in adult SPF P2 line (50-week-old) or commercial line (74-week-old) chickens inoculated with a virulent strain of Marek's disease virus (MDV). Commercial line chickens were given MDV vaccines (HVT and CVI 988) at hatch. The occurrence of MD was evaluated periodically by the evidence of neurologic signs such as paralysis, torticollis, ataxia, and/or nervous tics, as well as histopathological examination. In P2 line chickens, neurologic signs and MD lymphoma were observed from day 21 onward, and they tended to increase in a time-dependent manner. Meanwhile, in commercial line chickens, only one chicken exhibited MD lymphoma on day 70 post inoculation, but its pathogenesis was questionable. No regression of MD lymphoma was noted in either case. The lesions in the visceral organs, thymus, peripheral nerves, and feather pulps of P2 line chickens were characterized by proliferation of variably sized lymphoid cells. In the feather follicle epithelium, numerous inclusion bodies were noted on day 21 post-inoculation, which tended to decrease afterwards. The morphological findings obtained resembled late MD in field cases. In conclusion, our results demonstrate that adult SPF P2 line chickens are susceptible to virulent MDV, and would be useful for investigation of late MD.
authors.affiliation: Department of Pathogenic Veterinary Science, The United Graduated School of Veterinary Sciences, Gifu University, Gifu, Japan.
authors.forename: Mitsutaka
authors.initials: M
authors.lastname: Ikezawa
authors.forename: Masanobu
authors.initials: M
authors.lastname: Goryo
authors.forename: Jun
authors.initials: J
authors.lastname: Sasaki
authors.forename: Mohie
authors.initials: M
authors.lastname: Haridy
authors.forename: Kosuke
authors.initials: K
authors.lastname: Okada
mesh_terms: D000375:Aging; D000818:Animals; D002645:Chickens / Q000235:genetics; D020022:Genetic Predisposition to Disease; D025922:Mardivirus / Q000472:pathogenicity*; D008380:Marek Disease / Q000473:pathology / Q000517:prevention & control* / Q000821:virology; D022501:Marek Disease Vaccines / Q000276:immunology; D009412:Nerve Fibers / Q000473:pathology / Q000821:virology; D013047:Specific Pathogen-Free Organisms; D014774:Virulence
chemical_list: D022501:Marek Disease Vaccines