EPIDEMIOLOGIC EVIDENCE FOR AN INFECTIVE BASIS IN CHILDHOOD LEUKEMIA

An infective basis for childhood leukaemia is not a new suspicion (Kel lett, 1937). The failure of microbiologists to identify any specific a gent and of epidemiologists to demonstrate marked space-time clusterin g of the disease (Smith, 1382) have been discouraging, but neither is incompatible with an infectious origin. In several vertebrate species, the specific agents responsible for leukaemia belong to a class that is notoriously difficult to isolate. Also, many infectious illnesses d o not cluster because they are uncommon responses to the relevant infe ction. Thus, the agent responsible for infectious mononucleosis is mai nly spread not by those with the illness but by that very much larger number of infected individuals who are clinically unaffected (or only trivially so). Such infections can be considered as 'mainly immunising ': they can be seen as representing the most probable broad category t o which the infection underlying childhood leukaemia belongs.