© GARY W. CARTER/CORBISEvolution is supposed to occur slowly. But pathogens play by a different set of rules. Novel strains of bacteria and viruses can appear suddenly, or even jump from one host species to another to cause a disease outbreak, as is currently happening in China with an H7N9 strain of influenza virus. A central question in the study of emerging disease is whether novel pathogens will become more or less virulent toward their hosts the more time they spend with them. According to a new study from our group and others, at least one newly emerging pathogen—the bacterium Mycoplasma gallisepticum, or MG to those that study it—does both.
Our study, just published in PLOS Biology (11:e1001570, 2013), shows that MG, which affects the eyes of finches found in backyards across most of the United States, has rapidly and repeatedly evolved to become both more and less harmful to its songbird hosts. The complementary results reflect the different selective forces on the pathogen that occur as it spreads. In each case, the pathogen evolves to change the rate at which it kills its host in order to maximize the likelihood of infecting new hosts. The research provides some of the first clues suggesting that pathogen evolution can happen very rapidly, repeatedly, and also reversibly: under some conditions, the pathogen evolves to kill hosts more rapidly, while under others, virulence is attenuated.
The research provides ...
