PRNP and prion disease: Elucidation of (1) the mechanism of how IAV/WSN infection could induce the conversion of PrPC into PrPSc, (2) whether or not IAV/WSN infection in neurons could induce prion disease in animals, and (3) whether or not IAV infection in humans could be epidemiologically linked to sCJD are crucial for further understanding of the causative role of IAV infection in sporadic prion diseases.