S1 Subunit of Spike Protein from a Current Highly Virulent Porcine Epidemic Diarrhea Virus Is an Important Determinant of Virulence in Piglets

T.S. was partially supported by a grant from National Agricultural Research Organization. W.K. was supported by grants from The Ito Foundation and The Mishima Kaiun Memorial Foundation. Y.T. was supported by a grant from The Futaba Research Grant Program of the Futaba Foundation.