Response of meat-type chickens to infection with RAV-1 avian leukosis virus

Meat-type and White Leghorn chickens were inoculated with the RAV-1 strain of avian leukosis virus at 1 day of age and the severity of infection was assessed by clinical illness, haematology and post-mortem findings. The following were examined from selected birds: histological section for chronic mononuclear myocarditis, immunohistochemically-stained sections of myocardium, spleen, bursa of Fabricius and kidney for group-specific viral antigen, and ultrathin sections of these tissues for virus particles by electron microscopy. The experiment was terminated at 115-122 days. Approximately one-third of the 52 inoculated White Leghorns appeared anaemic at 3-4 weeks of age whereas there was no evidence of anaemia in 177 inoculated meat-type birds or in uninoculated birds of either type. Haemograms confirmed these observations. The first tumour found was a myelocytoma and it was in a meat-type bird at 65 days. Of the 151 meat-type birds of the inoculated group alive at 65 days, 8.5% developed nephroblastomas, but there were no cases of lymphoid leukosis. Myocarditis and virus replication in myocardium were usually more extensive in chickens that developed nephroblastomas than in those without such lesions. In 17 uninoculated control chickens examined between 26 and 122 days of age there were no virus particles or lesions in myocardium.