Historical background

The persisting ancient view of cancer as a contagious disease ended with 19 th century scientific investigations which seemed to show it was not. The r esulting dogma against an infectious cause for cancer produced great prejud ice in the scientific community against the first report of an oncogenic vi rus by Rous early in the 20th century and, even in tile 1950s, against Cros s's finding of a murine leukaemia virus and a murine virus causing solid tu mours. The Lucke frog renal carcinoma virus was the first cancer-associated herpesvirus. Intriguingly, an environmental factor, ambient temperature, d etermines virus genome expression in the poikilothermic frog cells. Althoug h an alpha -herpesvirus, Marek's disease virus of chickens shares some aspe cts of biological behaviour with Epstein-Barr virus (EBV) of man. Very sign ificantly, its lymphomas are the first naturally occurring malignancy to be controlled by an antiviral vaccine, with implications for human virus-asso ciated cancers. Tile circumstances and climate of opinion in which successi ve gamma -herpesviruses were discovered are described. The identification o f EBV involved two unconventionalities : its finding in cultured Burkitt's lymphoma cells when no human lymphoid cell had ever been maintained in vitr o, and its recognition in the absence of biological activity by the then ne w technique of electron microscopy These factors engendered hostility to it s acceptance as a new human tumour-associated virus. The EBV-like agents of Old World apes and monkeys and the T-lymphotropic gamma -herpesviruses of New World monkeys were found at about tile same time, not long after the di scovery of EBV. For many years these were thought to be the only gamma -her pesviruses of non-human primates; however, ver) recently B-lymphotropic EBV -like agents have been identified in New World species as well. Mouse herpe svirus 68 came to light by chance during a search for arboviruses and has b ecome important as a laboratory model because of its close genetic relatedn ess to EBV and its comparable biological behaviour. The discovery of Kaposi 's sarcoma-associated herpesvirus six years ago was made using unconvention al new methods, but, unlike with EBV 30) cars before, this did not hinder i ts acceptance. This contrast is discussed in the context of the great progr ess ill human tumour virology which has been made in recent) ears.