Submitted to: Avian Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/27/1998
Publication Date: N/A
Citation: Interpretive Summary: We have previously found that serotype 2 Marek's disease (MD) vaccine, a commonly used vaccine to control MD can enhance bursal lymphomas, a cancer-like condition induced by another virus termed avian leukosis virus (ALV). We have also found that certain lines of chickens may develop bursal lymphomas in absence of exposure to ALV (spontaneous bursal lymphomas). Our investigations revealed that serotype 2 MD vaccines may also enhance the development of spontaneous bursal lymphomas in certain lines of chickens. The information is useful to scientists in biomedical research who are studying the influence of herpesviruses on cancer and to poultry breeders and growers who are using serotype 2 MD vaccines in flocks that have not been exposed to ALV.
Technical Abstract: A significant incidence of bursal lymphoma with long latencies was noted in transgenic breeders carrying a benign defective subgroup A avian leukosis provirus, ALVA6, in their germline and maintained free of exposure to avian retroviruses. Serotype 2 Marek's disease (MD) vaccine virus, strain SB-1, a component of the bivalent MD vaccine used to vaccinate the breeders, was suspected as a contributory factor in the increased bursal lymphoma incidence. Although these bursal lymphomas had several characteristics similar to retroviral-induced bursal lymphomas, we found no evidence of retroviral influence based on many virological, immunological and molecular tests that were performed on plasma and tumor cells. These tumors were therefore classified as spontaneous bursal lymphomas, similar to those reported for some specific pathogen-free (SPF) chicken lines. Long-term in vivo experiments in plastic isolators and carefully maintained pens with homozygous and hemizygous ALVA6 and ALVA6-free female chickens (line 0) that were either non-vaccinated, serotype 3 (herpesvirus of turkeys (HVT); monovalent)-vaccinated, or HVT/SB-1 (bivalent) vaccinated, demonstrated that the incidence of spontaneous bursal lymphomas were significantly higher in those chickens that were vaccinated with the bivalent MD vaccine (P<0.05). The data suggest that the increased incidence of spontaneous bursal lymphomas is correlated solely with the presence of SB-1 and is not dependent on the presence of ALVA6.