When viruses become more virulent

Abstract

Natural selection favors virulence when it is coupled with increased viral transmission

Abstract

The evolution of virulence—the degree to which a pathogen sickens, kills, or otherwise reduces its host’s fitness—depends on the biology of infection and transmission ( 1 ). A more virulent virus may be less transmissible because in killing its host, it reduces the opportunity for transmission. But virulence and transmissibility can be intrinsically linked, so that to maintain or increase infectiousness, a virus must be virulent. On page 540 of this issue, Wymant et al. ( 2 ) describe the emergence of a more virulent and transmissible variant of HIV that has spread to 102 known cases, mostly in the Netherlands, over the past decade. This finding raises questions about the selective pressures and molecular mechanisms that drive increased virulence and transmission.