The microbiome and its role in health and disease has been the subject of extensive research; however, the role of the virome in host physiology beyond causing acute infections has been studied to a lesser extent. A recent study reported several homologues of human hormones and growth factors encoded in viral genomes. The authors searched public genome databases for viral peptide sequences that shared homology with human hormones, growth factors or cytokines and found 16 full-length sequences that encode homologues, including four insulin-like growth factor 1 (IGF1) peptides. Synthetic viral IGF1 peptides bound to human and mouse insulin and to IGF1 receptors in vitro, stimulating downstream signalling and increasing glucose uptake and cell growth. Injection of the viral peptides into mice lowered blood glucose levels, indicating that viruses may modulate host physiology by mimicking mammalian hormones.