We would like to present the abstract of our keynote speaker – Ethel-Michele de Villiers – who has actively been engaged in the identification and analyses of single-stranded circular human DNA-viruses and also characterized a large number of novel human papillomavirus types.
Over the years a large variety of laboratory methods have been used to isolate unknown infectious agents. The conservative methods included partial purification, susceptibility for replication in cell culture, electron microscopy and/or density gradient centrifugation, just to mention a few. These were all in part biased and limited to available experimental methods. With the advent of the polymerase chain reaction and sequencing, many viruses could initially be identified via their genomic characteristics, followed, if possible by biological analyses. The most recent application of whole genome sequencing of samples with or without partial purification, gives insight into a whole new spectrum of infectious agents. This novel information also stresses the point that historical divisions between animal, plant and bacterial “viruses” are outdated. Several examples will be reviewed in short.
In our present study a combination of density purification and genomic amplification led to the identification of circular single-stranded DNA molecules in bovine serum and dairy products (BMMF-bovine milk and meat factors), as well as serum and brain samples from patients with multiple sclerosis. These isolates were grouped into 4 groups according to their relatedness. Several characteristics were identified which had previously been described for bacterial plasmids or plant viruses or human viruses. These will be discussed in more detail. Replication in human cells of the DNA isolates with characteristics of bacterial plasmids was demonstrated by transfection.