A 32-amino-acid deletion in the nonstructural protein 3-coding region of porcine epidemic diarrhea virus is associated with clinical attenuation in piglets

Abstract Since the global emergence of highly pathogenic genotype 2b (HP-G2b) porcine epidemic diarrhea virus (PEDV) strains in 2013, these viruses have become endemic in South Korea. During local outbreaks, novel HP-G2b PEDV variants containing a 32-amino acid deletion (DEL) in nonstructural protein 3 (nsp3), designated NSP3-DEL32, were identified in several affected farms with low neonatal mortality. To examine the effect of NSP3-DEL32 on PEDV virulence, a recombinant PEDV, icNSP3-DEL32, was generated harboring the same DEL signature in nsp3 using the HP-G2b icKNU-141112 strain as the backbone. The growth properties of icNSP3-DEL32 were comparable to those of icKNU-141112 in interferon (IFN)-deficient cells. However, in IFN-responsive cells, icNSP3-DEL32 replicated less efficiently but induced higher levels of IFN responses than icKNU-141112. Animal challenge experiments revealed notable differences in pathogenesis between icKNU-141112 and icNSP3-DEL32. Infection with icKNU-141112 resulted in 100% mortality, whereas icNSP3-DEL32 infection caused a lower mortality rate (60%). Remarkably, two piglets inoculated with icNSP3-DEL32 survived and exhibited decreased viral loads as well as normal macroscopic and microscopic intestinal findings, indicating reduced enteropathogenicity of icNSP3-DEL32. These findings indicate that naturally occurring DEL32 in nsp3 partially attenuates PEDV in piglets and support a role for nsp3 as a virulence determinant that suppresses IFN responses.