ISG15 and infection: Infections with both EHI0418Y05 and EHI0169Y07 elicited a significant rise in IFN-β transcript (p ≤ 0.001) (Figure 3B), but IFN-stimulated genes, IFITM1, RSAD2, and ISG15, were expressed at higher levels following infection with EHI0418Y05 than with EHI0169Y07 (Figure 3C–E).