Responses of Isolator-Derived and Conventional Chickens to Marek's Disease Herpesvirus and Avian Leukosis Virus 2

Abstract

A flock of isolator-derived, barrier-sustained specific-pathogen-free, White Leghorn chickens (LSI-SPF) was developed to provide definitive biologic materials for the study of avian tumor viruses, particularly Marek's disease herpesvirus (MDHV) and avian leukosis virus (ALV). Unlike conventional birds, LSI-SPF chickens inoculated with MDHV died as early as 10 days afterward and mortality reached 100% within 12–22 days post inoculation. The time to death was related to the dose of MDHV. Typical Marek's disease (MD) symptoms and gross tumors were not seen before death. In sharp contrast, neither mortality nor tumors were observed among LSI-SPF chickens contact-exposed to birds with MD. Persistent viremia and neutralizing antibodies demonstrated that infection had occurred in LSI-SPF birds. LSI-SPF chickens kept 8 weeks in an ALV-monocontaminated environment had neither symptoms nor tumors, although ALV viremia was demonstrated. The only experimental condition in which mortality (81%) and tumor development (100%) occurred in LSI-SPF chickens was concurrent exposure to both MDHV and ALV.