Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 12, 1995
Publication Date: N/A
Interpretive Summary: Marek's disease and lymphoid leukosis are the two most common economically important virus-induced, cancer-like diseases of chickens. Vaccines containing two different types of Marek's disease virus are widely used to protect chickens against Marek's disease. Recently, we have shown that vaccination of chickens with certain Marek's disease vaccines may increase the incidence of lymphoid leukosis. The mechanism of increasing the incidence of lymphoid leukosis by Marek's disease vaccine is poorly understood. In this study, we determined the effects of two different Marek's disease vaccine viruses on the development of early lesions of lymphoid leukosis and examined the relationship between the vaccine and the developing tumor. Results suggest that the increased frequency of lymphoid leukosis is probably due to an effect of Marek's disease vaccine virus at the early stage of lymphoid leukosis tumor formation. The information should add significantly to the understanding of the mechanism of interaction between two different types of tumor viruses and should help in developing safer vaccines for Marek's disease.
Technical Abstract: Previous studies have shown that serotype 2 Marek's disease virus (MDV) augments the development of avian leukosis virus (ALV)- induced lymphoid leukosis (LL). In the present study, we determined the effect of serotype 2 and 3 MDV on the development of ALV-induced preneoplastic bursal lesions. Chickens were inoculated at hatch with strain 301B/1 of serotype 2 MDV or strain FC126 of turkey herpesvirus (HVT), a serotype 3 MDV. Chickens were also inoculated at hatch with strain Rous-associated virus-1 (RAV-1) or strain RPL-40 of subgroup A ALV. At 11 and 14 weeks of age, serial sections of bursal tissues from chickens in various treatment groups were stained with methyl green-pyronine and examined for ALV-induced preneoplastic bursal lesions, also known as hyperplastic follicles (HF). Bursal tissues from groups of chickens inoculated with serotype 2 MDV and ALV at hatch were also examined for the presence of MDV genome by in situ hybridization analysis. The incidence of ALV-induced HF was significantly higher in chickens inoculated with serotype 2 MDV than in uninoculated chickens or chickens inoculated with HVT. In contrast, the lowest incidence of HF was noted in chickens treated with HVT. In situ hybridization analysis of bursal tissues from 11- and 14-week-old chickens infected with serotype 2 MDV and ALV at hatch revealed that the MDV is closely associated with ALV-induced HF. The data suggest that the enhancing effect of MDV on ALV-induced lymphomagenesis may be at the stage of formation of HF in the bursa and that persistent MDV infection of ALV transformed bursal cells may be necessary for enhancement of LL.