As shown in Fig. 1F and G, rJ2.2.4a and rJ2.2.8b (rj2.2 expressing protein 4a or protein 8b) infections resulted in enhanced virulence in mice, but not recombinant viruses inserted with ORF3, ORF4b, and ORF5, as determined by more weight loss and greater mortality. This evidence concerns the gene ASZ1 and infection.