Experimental infection of chickens with an australian strain of reticuloendotheliosis virus. I. Clinical, pathological and haematological effects.

A wide range of clinical, pathological and haematological effects were found over a 40-week period in chickens inoculated at 1-day-old with a low-passage, cell-culture preparation of an Australian strain of reticuloendotheliosis virus. Feathering defects and statistically significant depression of body weights occurred in chickens up to 8 weeks of age. Other findings in birds that died or were culled during the 40-week experimental period included mild anaemia, leucopenia, heterophilia, hypoplasia of immune system organs, inflammation in visceral and nervous system organs, and bacterial or fungal infections. These results suggested that ill-thrift and death in some chickens infected with reticuloendotheliosis virus may be due to secondary infections with microorganisms subsequent to damage of immune system organs by that virus. Lymphoreticular-cell tumours of the liver, kidney or spleen were found in two birds aged 22 and 24 weeks. These results establish reticuloendotheliosis virus as a possible cause of tumours in adult fowls. Horizontal transmission of virus was demonstrated but the only abnormalities detected in the in-contact chickens were feathering defects.