Attempts to Detect RNA Tumour Virus in Human Milk

ONCORNAVIRUS-like morphological structures and particulate material containing RNA-directed DNA polymerase (RDP) activity in association with 70S RNA (commonly referred to as the simultaneous detection1) have been reported in some human milks2-7. However, other workers concluded from electron microscopic studies of human milk that the particles observed were probably cytoplasmic debris and not type-B or type-C virus particles8,9. In addition, the partially purified RDP activity of human milk differed in chromatographic behaviour from that of known animal oncornaviruses10. Thus, the viral origin of the RDP activity measured in human milk remains in doubt. We report here the occurrence of particulate RDP in association with high molecular weight RNA in a small number of human milk samples with no correlation with presence of oncornavirus particles by electron microscopy or with a family history of breast cancer. By contrast, we were able to correlate the presence of high molecular weight RNA and RDP activity with morphologically detectable type-B and type-C oncornaviruses from the milk of freshly trapped wild mice.