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Interest in the human microbiome has been concentrated largely on “commensal” bacteria. But humans also harbor many resident viruses that might affect human health, not by infecting and damaging human tissue nor by eliciting destructive immune responses, but by making molecules that affect human physiology.
In a new report, researchers describe four viruses — members of the Iridoviridae family — in human blood and feces, whose genes produce peptide hormones that closely resemble human insulin and insulin-like growth factors (IGFs). These peptides bind to human receptors and stimulate their downstream signaling, increase glucose uptake by adipocytes in vitro, and lower blood glucose when injected into mice. The viral molecules also stimulate …