I agree this is not a model I am familiar with, generally speaking the highest virulence is evinced in the index case generation. As any virus optimizes itself to a new host as is the case with influenza being zoonotic, it becomes less virulent in every generation of it's lifecycle. This is not a result of evoloving a new or enhanced biological transmission mechanism
Kelly, as I understand it, some viruses become more, not less, virulent in new generations. As far as I have been able to determine, there is no way to tell which way it will jump.