Antibody response elicited against empty reticuloendotheliosis virus particles in two inbred lines of chicken

An outbreak of lymphomas in commercial broiler breeder chickens vaccinated with a fowlpox vaccine contaminated with reticuloendotheliosis virus

Gross and microscopic examinations of affected tissues from chickens of two commercial broiler breeder flocks aged 27 and 31 weeks revealed lesions of visceral lymphomas with bursal involvement in some chickens. Reticuloendotheliosis virus (REV), but not avian leukosis virus (ALV), was isolated from blood of affected chickens. Furthermore, DNA extracted from tumours tested positive for REV, but not for ALV or Marek's disease virus by polymerase chain reaction (PCR) test. Attempts to determine the source of REV infection included testing a commercial fowlpox (FP) vaccine used to immunize flocks at 7 days of age. Chicken-embryo fibroblasts inoculated with the FP vaccine tested positive for REV by PCR and immunofluorescent tests. REV was also isolated from plasma of pathogen-free chickens experimentally inoculated with FP vaccine at hatch; two of eight (25%) inoculated chickens developed lymphomas by 34 weeks of age. Antigenic characterization of REV isolated from commercial broiler breeder chickens and from FP vaccine, using monoclonal antibodies, revealed that both isolates belong to subtype 3 of REV. The data represent the first report of an outbreak of REV-induced lymphomas in commercial chickens. The data also indicate that the source of REV infection is an REV-contaminated commercial FP vaccine.

Avian retroviruses

Avian leukosis virus (ALV) and reticuloendotheliosis virus (REV) are the most common naturally occurring avian retroviruses associated with neoplastic disease conditions in domesticated poultry. Avian leukosis virus infects primarily chickens, whereas REV infects chickens, turkeys, and other avian species. In addition to causing tumors, both ALV and REV can reduce productivity and induce immunosuppression and other production problems in affected flocks.