The dark matter of microbiome: the mother-infant pair virome.

The human virome belongs to one of the most complex ecosystems in the world, the microbiome. The virome that inhabits the intestinal niche and its dynamic variation during the first year of life had been the most investigated. Many pathogenic viruses are well known to be potentially transmitted transplacentally or during vaginal delivery to the newborn, but recent studies on healthy term pregnancies found that there was no evidence of a principal viral community. In the maternalfetal dyad, human milk has been demonstrated to be one of the earliest factors involved in the direct virome transmission. Despite the relationship between humans and viruses traces its roots back to ancient times, the mother-infant pair virome has been poorly investigated and represents currently a "dark matter" of the microbiome.