Detection of reticuloendotheliosis virus as a contaminant of fowl pox vaccines.

This study was designed to detect reticuloendotheliosis virus (REV) as a contaminant in fowl pox vaccines. A total of 30 fowl pox vaccine samples were examined for the presence of REV using both in vitro and in vivo methods. In in vitro testing, the fowl pox vaccine samples were inoculated into chicken embryo fibroblast cultures prepared from specific-pathogen-free embryonated chicken eggs, and the cultures were examined using PCR to detect REV. In in vivo testing, each fowl pox vaccine sample was inoculated into 5-d-old specific-pathogen-free chicks, which were kept under observation for up to 12 wk postinoculation; serum samples were collected at 15, 30, and 45 d postinoculation for the detection of REV-specific antibodies using ELISA. Tissue samples were collected at 8 and 12 wk postinoculation for histopathological examination. Of the tested vaccines, only one imported vaccine sample tested positive for REV using PCR. Serum samples collected from chicks infected with the PCR-positive vaccine batch also tested positive for REV-specific antibodies using ELISA. Histopathological examination of the liver, spleen, and bursa of Fabricius demonstrated the presence of tumor cells in these organs, confirming the results obtained using PCR and ELISA, and indicating that the sample was contaminated with REV. These data clearly indicate that the screening of all commercial poultry vaccines for viruses is an important factor in assuring the biosafety of animal vaccines.