This week’s paper is “Local interactions select for lower pathogen infectivity” by Michael Boots and Michael Mealor, University of Sheffield, published in Science (vol. 315, pgs. 1284-1286) and suggested by my wife.
The evolution of greater or lesser infectiousness in pathogens has important implications for health of plants and animals, including humans. Evolution is a process that follows its own rules and humans can’t control it completely, but we can sometimes influence it, just as we may be able to constrain the course of a river or limit the spread of a forest fire.
One factor over which we have some control is the ease with which a pathogen spreads from one host individual to another. For example, a bacterium on the skin of one patient in a hospital can’t jump to another patient in a different room, but it may be able to hitch a ride with a doctor or nurse who forgets to change gloves between patients. Intestinal bacteria reach new hosts easily if untreated sewage is dumped into the same river used for drinking water, even if the bacterium is so virulent that the host is too sick to walk around and infect others.
Paul Ewald has suggested that easy transfer between hosts favors the evolution of greater virulence (Oxford Surveys in Evolutionary Biology 5:215-245). For example, cholera spreading through South America in 1991 evolved greater virulence in countries with poor water supplies, but lesser virulence in countries with better water supplies. So not only were more people infected in countries with polluted water supplies, but the infected people were sicker.
Continue reading "Less-vicious viruses evolve in viscous cannibal populations" »
