Isolation and characterization of Korean porcine deltacoronavirus strain KNU16-07

Jang, Guehwan; Kim, Seong-Hee; Lee, Yoo Jin; Kim, Seungjoon; Lee, Du Sik; Lee, Kyoung-Ki; Lee, Changhee

The PDCoV-challenged piglets exhibited clinical signs including diarrheic feces and lethargy by 2 days post-inoculation (dpi) and then displayed vomiting and diarrhea for 3 days. All inoculated animals were positive for PDCoV, as determined by quantitative RT-PCR, at 1 or 2 dpi, and they shed PDCoV in feces. Peak mean Ct values of 16.8 (range, 16.7-16.8) and 18.7 (range, 18.5-18.9) were obtained at 3 to 4 dpi. The negative control pig remained active with normal feces and no fecal shedding of PDCoV detected throughout the study period. Two animals were independently euthanatized at 3 and 5 dpi for postmortem assessments, whereas the remaining piglets were necropsied at 35 dpi. Unlike the negative control piglet, all challenged piglets exhibited typical PDCoV-like macroscopic observations with thin and transparent small intestine walls (panel A in Fig. 2) . The inoculated pigs also developed histopathological intestinal lesions associated with viral enteritis, including shortened and fused villi in the small intestine (panels B and C in Fig. 2) . Furthermore, an immunohistochemistry assay detected PDCoV in the cytoplasm of villous enterocytes throughout the small intestines (panel D in Fig. 2) . These macroscopic and microscopic observations are consistent with previous studies using USA PDCoV isolates [1, 5] . Taken together, the results show that experimental infection of newborn piglets with PDCoV KNU16-07 induces clinical disease signs corresponding to acute enteritis, indicating enteropathogenicity of the isolate in the natural host. Additionally, all inoculated pigs had detectable PDCoV-specific neutralizing antibody (NA) by 14 dpi and maintained high NA titers of 1:128 to 1:256 thereafter, demonstrating the ability of KNU16-07 to induce efficient immune responses.