Identification and Characterization of Circular Single-Stranded DNA Genomes in Sheep and Goat Milk

In recent years, a variety of circular replicase-encoding single-stranded (CRESS) DNA viruses and unclassified virus-like DNA elements have been discovered in a broad range of animal species and environmental samples. Key questions to be answered concern their presence in the human diet and their potential impact on disease emergence. Especially DNA elements termed bovine meat and milk factors (BMMF) are suspected to act as co-factors in the development of colon and breast cancer. To expand our knowledge on the occurrence of these potential pathogens in human nutrition, a total of 73 sheep and 40 goat milk samples were assayed by combining rolling circle amplification (RCA), PCR and Sanger sequencing. The present study further includes retail milk from the aforementioned species. We recovered 15 single stranded (ss) circular genomes. Of those, nine belong to the family Genomoviridae and six are members of the unclassified group of BMMF. Thus, dairy sheep and goats add to dispersal of CRESS viruses and circular ssDNA elements, which enter the food chain via milk. The presence of these entities is therefore more widespread in Bovidae than initially assumed and seems to be part of the common human nutrition.