Backseat drivers: the hidden influence of microbial viruses on disease

► Viruses parasitising human pathogens contribute virulence to achieve symbiosis. ► We call this relationship 'hyperpathogenism' and present its wide clinical potential. ► We review its impact on human disease, using Leishmania RNA virus as an example. ► We discuss conditions of the evolutionary sanctuaries breeding hyperpathogenism. ► Concluding its importance as a target for diagnostic and therapeutic intervention.