Characterization and pathogenicity of Vero cell-attenuated porcine epidemic diarrhea virus CT strain

Abstract

BackgroundPorcine epidemic diarrhea virus (PEDV) has caused enormous economic losses to the global pig industry. Currently available PEDV vaccine strains have limited protective effects against PEDV variant strains.MethodsIn this study, the highly virulent epidemic virus strain CT was serially passaged in Vero cells for up to 120 generations (P120). Characterization of the different passages revealed that compared with P10 and P64, P120 had a higher viral titer and more obvious cytopathic effects, thereby demonstrating better cell adaptability.ResultsPathogenicity experiments using P120 in piglets revealed significant reductions in clinical symptoms, histopathological lesions, and intestinal PEDV antigen distribution; the piglet survival rate in the P120 group was 100%. Furthermore, whole-genome sequencing identified 13 amino acid changes in P120, which might be responsible for the attenuated virulence of P120.ConclusionsThus, an attenuated strain was obtained via cell passaging and that this strain could be used in preparing attenuated vaccines.

Porcine epidemic diarrhea virus (PEDV): An update on etiology, transmission, pathogenesis, and prevention and control

“…Four-day-old CDCD pigs orally inoculated with 2 log 10 PFU of PC22A (140th-160th) showed low to moderate fecal viral RNA shedding titers, with mild villous atrophy (Lin et al, 2017a) (Table 2). Sixday-old conventional pigs orally inoculated with 6 log 10 TCID 50 of G2b PEDV CT (120th passage in Vero cells) showed mild diarrhea and moderate fecal viral RNA shedding titers, with mild villous atrophy (Wu et al, 2019). On the other hand, pregnant sows orally inoculated with G1a PEDV DR13 (100th passage in Vero cells) showed no clinical signs but high VN antibody levels in the colostrum (Song et al, 2007).…”

“…In addition, PEDV variants of mild virulence, such as the S1 N-terminal domain (NTD)-Del variant, also occurred naturally (Su et al, 2018;Suzuki et al, 2016;Zhang et al, 2018a). PEDV strains fully adapted to Vero cells and serially passaged at least 70 times (with trypsin or GCDCA in the cell culture medium) tended to replicate less efficiently in the intestine of pigs (Chen et al, 2015;Kim et al, 2017a;Lin et al, 2017a;Sato et al, 2011;Wu et al, 2019) (Table 2) and elicited low serum PEDV-specific antibody titers (Lin et al, 2017a). Twelve-week-old pigs orally inoculated with 8.2 log 10 TCID 50 of G1a PEDV 83P-5 (100th passage in Vero cells) exhibited only intermittent fecal viral RNA shedding in 3 of 4 pigs (Sato et al, 2011).…”

Characteristics and Pathogenicity of the Cell-Adapted Attenuated Porcine Epidemic Diarrhea Virus of the Non-S INDEL Cluster

“…On day 3 post-inoculation, the mean virus shedding in group 4 piglets was 10 4.51 -fold lower than that in the group 1 piglets. Previous studies have shown that viral shedding titers are highest from days 3 to 4 post-challenge, and on these days, pathogenic signs were the clearest [29][30][31][32]. On day 4 post-inoculation, piglets from each group were necropsied to observe the lesions in the small intestines (Figure 3C).…”

Porcine epidemic diarrhea virus: Molecular mechanisms of attenuation and vaccines

“…The highly virulent epidemic virus strain CT was serially passaged in Vero cells up to 120 passages (P120), and P120 had a higher viral titer and better cell adaptability with more obvious cytopathic effects. In addition, P120 showed significant reductions in clinical symptoms with 100% survival rate in piglets [ 2 ].…”

“…PEDV mainly infects the porcine intestinal epithelial cells. Then, PEDV colonizing the intestines results in atrophy, necrosis, and shedding of intestinal villi, which affected the absorption of nutrients, leading to vomiting, diarrhea, weight loss, anorexia, and depression [ 2 , 3 ]. When PEDV is excreted into the environment with feces, the contaminated feces may result in a mass epidemic.…”