Mechanisms of viral transmissions are sometimes correlated with genetic diversity dynamics. For example, hepatitis C viruses transmitted by drug injection or blood products have a faster rate of spread than endemic strains circulating in Asia and Africa [32] . It has also been suggested that mosquito susceptibility may affect the growth of dengue viruses [33] . Therefore, it is possible that a change of host species could generate the difference in the viral dynamics we observe. In our study, the majority of the reassortant viruses (24/25) were isolated from humans, whereas only a minority of the group 2 viruses were isolated from humans (10/57 and 10/41 in the HA and NA datasets, respectively).