The long view: 40 years of avian leukosis research.

The present review is aimed at the non-specialist reader and is one of a number being written on important diseases of poultry to celebrate the 40th anniversary of the birth of Avian Pathology, the journal of the World Veterinary Poultry Association. The diseases of the avian leukosis complex have a number of features of distinction. They were the first neoplastic diseases in any species to be shown, 100 years ago, to be transmissible and caused by viruses, and have consequently been studied extensively by biomedical scientists as models for the role of viruses in cancer. They also became, from around the 1920s, the major cause of mortality and economic loss to the developed poultry industry, and were studied by agricultural scientists searching to understand and control them. The remit of the review is to cover research carried out over the 40 years since 1971, when the journal was founded. In this review on avian leukosis, an introductory summary is given of knowledge acquired over the preceding 60 years. Subsequently a selection is provided of discoveries, both fundamental and more applied, that seem to us to be of particular importance and interest. Much of the work was carried out by biomedical scientists interested in cancer. Probably the most significant was the discovery in the avian retroviruses of oncogenes that cause leukosis and other tumours and of their origin from proto-oncogenes in normal cells. These oncogenes are involved in cancer in many species, including chickens and humans. Other work was performed by agricultural scientists interested in poultry disease. Interests of the two groups have overlapped, particularly as a result of a shift of emphasis to molecular biology research.