Novel Infectious Agents in Dairy Cattle and their Potential Role in Human Chronic Diseases Harald zur Hausen and Ethel-Michele de Villiers, Deutsches Krebsforschungszentrum, Im Neuenheimer Feld 280, 69120 Heidelberg, Germany Geographic epidemiology of colon and breast cancers points to red meat and milk products derived from dairy cattle as potential risk factors for these cancers (zur Hausen and de Villiers, 2015, zur Hausen 2015). The analysis of sera and dairy products from dairy cows resulted in the isolation of 22 novel virus-like single-stranded circular DNAs which range in size between 1084 and 2958 nucleotides. They seem to persist episomally and represent members of three different families. Two of the latter contain an open reading frame related to a bacterial plasmid. Transfection experiments have been performed in human cells in order to exclude bacterial contamination as origin. All genomes which have been tested up to now are genetically active in human cells. Characterization of the transcribed RNA points to adaptation of these agents to mammalian cells. Presently, their protein expression and host reactivity to expressed proteins are being analyzed. The isolation of two of these agents from lesions of patients with multiple sclerosis is also directing our interest to a potential involvement of some of these agents in neurodegenerative diseases. References: zur Hausen, H. and de Villiers, E.M. Dairy cattle serum and milk factors contributing to the risk of colon and breast cancers. Int J Cancer. 2015; 137: 959-967 zur Hausen, H. What do breast and CRC cancers and MS have in common? Nature Rev. Clinical Oncology, 2015; 12: 569-70.