I guess host-to-virus and virus-to-host is what I meant with the question. Virus evolves in the herring incorporating the AFP gene. Then infects the smelt or

I guess host-to-virus and virus-to-host is what I meant with the question. Virus evolves in the herring incorporating the AFP gene. Then infects the smelt or gametes and injects the AFP gene. A small number of smelt incorporate the gene and then nature selects for their offspring.