Comparative analysis estimates the relative frequencies of co-divergence and cross-species transmission within viral families

Geoghegan, Jemma L.; Duchêne, Sebastián; Holmes, Edward C.

Emerging pathogens that cross the species barrier to infect new hosts can profoundly affect human and animal health, as well as wildlife and the agricultural industries. Although most emerging diseases seemingly result from such a process of cross-species transmission, it is also the case that some viruses seem to rarely jump the species barrier and instead co-diverge with their hosts over long stretches of evolutionary time. For example, long-term virus-host codivergence has been suggested to play a key role in the evolution of vertebrate herpesviruses over periods of~400 million years [1] and insect baculoviruses over a time-scale of~310 million years [2] . Indeed, it has been proposed that a number of families of DNA viruses have codiverged with their hosts over long evolutionary time-scales [3] [4] [5] , and do so more frequently than RNA viruses, which in contrast display a combination of co-divergence and host switching [6] . In particular, while phylogenetic trees for some RNA viruses, such as particular retroviruses, are generally congruent with those from their hosts suggesting long-term codivergence [7] , for others, such as flaviviruses, host jumping appears to be relatively frequent [8] . In the case of flaviviruses this likely in part reflects the fact that many are transmitted by arthropod vectors and characterized by short durations of infection. The situation appears to be even more complex in cases such as the hantaviruses where there is evidence of both codivergence and host jumping [6] .