First Insights into the Occurrence of Circular Single-Stranded DNA Genomes in Asian and African Cattle

SIMPLE SUMMARY: Since 2014, a special class of meat and milk-derived circular DNA agents—termed bovine meat and milk factors (BMMF)—has been linked to the process of indirect carcinogenesis in humans. These BMMF include members of the virus family Genomoviridae, as well as unclassified DNA elements exhibiting both viral and plasmid attributes. Initial detection of BMMF in European cattle samples led to the assumption that BMMF are exclusively present in aurochs-derived cattle and consequently in food produced thereof. In the meantime, a more widespread occurrence including water buffalo, sheep and goat milk has been shown. The aim of the present study was to broaden our knowledge concerning the BMMF occurrence in different and less domesticated ruminants like yaks, zebus and watusi cattle that serve for food production in various countries. The predominant detection of BMMF in fecal matter compared to blood provides novel clues regarding the origin and transmission routes of these entities finally reaching the food chain. ABSTRACT: Circular replicase-encoding single-stranded (CRESS) DNA viruses and other circular DNA agents are increasingly found in various samples and animals. A specific class of these agents—termed bovine meat and milk factors (BMMF)—has been supposed to act as a factor in indirect carcinogenesis in humans. Initial observations attributed the BMMF to European cattle breeds and foodstuffs produced thereof. In the present study, blood and fecal samples from African and Asian cattle were examined. BMMF molecules and genomoviruses were detected in all bovids under study. The majority (79%) of the 29 circular elements could be assigned to BMMF groups 1 and 2, whereas CRESS viruses of the family Genomoviridae accounted for the smaller part (21%). Two genomoviruses belong to the genus Gemykibivirus and one to the genus Gemykrogvirus. The remaining three might be considered as novel species within the genus Gemycircularvirus. The majority of all isolated molecules originated from fecal samples, whereas only three derived from blood. The results from this study expand our knowledge on the diversity and presence of circular DNA in different ruminants that serve for food production in many countries over the world.