11 The Search for Human RNA Tumor Viruses

Abstract

I. INTRODUCTION
With the realization that retrovirus infections are widespread among vertebrate hosts, including some primate species, the search for human retroviruses has not been thwarted through lack of effort. Throughout the 1960s and 1970s, numerous claims have been made for evidence of human retrovirus infection; some proved to involve genuine retroviruses but not human, others were not upheld by more detailed investigation, and still others remain enigmatic as to the provenance of the viruses. At this time, however, it would appear that at least two distinct retroviruses occur as natural infections of human populations. One is a foamy virus (see Chapter 2) with no known associated disease. The other is a C-type oncovirus associated with certain forms of adult T-cell leukemia and lymphoma (see Section V).

A. Epidemiology
Epidemiological studies have not been very helpful in allocating an infectious etiology to human tumors. With most infectious diseases, the transmissible nature of the illness had been obvious before the particular agent was discovered. There have been reports of remarkable clusters in the incidence of children’s leukemia and of Hodgkin’s disease suggestive of infective transmission (Heath and Hasterlik 1963; Vianna et al. 1971; Dworsky and Henderson 1974; Schimpff et al. 1975), but these studies have been criticized methodologically (Smith and Pike 1976; Mack 1980) and have not been upheld by case-control studies (Alderson and Nayak 1971; Kryscio et al. 1973; P.G. Smith et al. 1977; Alderson 1980). Recent epidemiological evidence of an endemic area in Japan (Uchiyama et al. 1977; Tajima...