Characterization and pathogenicity of Vero cell-attenuated porcine epidemic diarrhea virus CT strain
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RESEARCH
Open Access
Characterization and pathogenicity of Vero cell-attenuated porcine epidemic diarrhea virus CT strain Yu Wu1, Wei Li2, Qingfeng Zhou2, Qunhui Li2, Zhichao Xu2, Hanqin Shen2 and Feng Chen1,2*
Abstract Background: Porcine 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. Methods: In 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. Results: Pathogenicity 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. Conclusions: Thus, an attenuated strain was obtained via cell passaging and that this strain could be used in preparing attenuated vaccines. Keywords: Porcine epidemic diarrhea virus, Attenuation, Pathogenicity, Genome, Sequence analysis
Background Porcine epidemic diarrhea (PED) is an acute and highly infectious intestinal disease in pigs; it is caused by porcine epidemic diarrhea virus (PEDV), which has caused enormous economic losses to the global pig industry [1, 2]. PED is characterized by diarrhea, vomiting, dehydration, anorexia, weight loss, and high mortality in suckling pigs. Although PED also appears in summer, it mainly occurs in winter. PEDV infection causes different symptoms according to the pigs’ ages; however, in piglets, the symptoms of PEDV infection are particularly serious, including a high mortality rate [3]. PEDV belongs to the order Nidovirales, family Coronaviridae, and genus Alphacoronavirus and is an enveloped virus with a single-stranded, positive-sense RNA genome [2]. The whole PEDV genome is approximately 28 kb * Correspondence: [email protected] 1 College of Animal Science, South China Agricultural University & Guangdong Provincial Key Lab of Agro-Animal Genomics and Molecular Breeding, Guangzhou 510642, People’s Republic of China 2 Wen’s Group Academy, Wen’s Foodstuffs Group Co., Ltd., Xinxing 527400, Guangdong, China
nucleotides (nts) long and has a 5′-cap and 3′-polyadenosyl tail; the genome also includes 5′- and 3′-untranslated regions and at least 7 open reading frames (ORF1a, ORF1b, and ORF2–6) [4, 5]. ORF1a and ORF1b encode the replicase polyproteins 1a and 1ab, respectively, which undergo autoproteolysis by viral proteases to form 16 nonstructural proteins (Nspl–16) [6], which participate in the basic mechanisms of viral RNA transcription and replication. ORF2–6 encode four structural proteins [fibrin (S), membrane protein (M), envelope pro
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