RETROVIRAL ETIOPATHOGENESIS OF OVINE PULMONARY-CARCINOMA - A CRITICAL-APPRAISAL

Although it has long been thought that a retrovirus is the responsible agent for ovine pulmonary carcinoma (OPC), identification of a replic ative viral agent has proven difficult. Recently, the genome of a new retrovirus, jaagsiekte sheep retrovirus (JSRV), found in the lung-wash of affected sheep lung, has been cloned and sequenced; characterizati on of this virus and its consistent presence in turner cells argue for - its role as the aetiologic agent of OPC. Analysis of the nucleic aci d sequence of the JSRV genome, suggests a new class of retro virus. on e that is chimeric according to the morphological classification schem e used for retroviruses. The genome of this virus does not appear to c ontain an oncogene, and the mechanism by which it causes disease is st ill unknown. The presence of multiple copies of endogenous retroviruse s related to JSRV in DNA of OPC-affected and unaffected sheep further complicates investigation of oncogenesis in OPC. This review examines the evidence for a retrovirus as the causative agent for OPC, with par ticular emphasis on the viruses studied to date. The significance of e ndogenous JSRV-related sequences is considered. The mechanisms by whic h a retro virus such as JSRV might induce lung rumours in sheep, and w hich of these are most likely, are discussed in light of these develop ments, as are the prospects for new means of diagnosis and treatment o f this disease.