Differences in the pathogenicity of Chinese virulent genotype GIIa and GIIb porcine epidemic diarrhea virus strains and the humoral immune status of one- and two-month-old weaned pigs infected with these strains

Evaluation of the immunoprotective effects of porcine deltacoronavirus subunit vaccines

Porcine deltacoronavirus (PDCoV), a new porcine enteric coronavirus, has seriously endangered the pig breeding industry and caused great economic losses. However, a PDCoV vaccine is not commercially available. Therefore, new and efficient PDCoV vaccines must be developed without delay. In this study, we used the ExpiCHO eukaryotic expression system to express and purify the following 3 structural proteins of PDCoV: S, N and M. Subsequently, the level of humoral and cellular immunity induced by the S protein (immunization with the S protein alone) and a protein mixture (immunization with a mixture of S, N and M proteins) were evaluated in mice and piglets, respectively, and the performances of the 2 immunizations in a challenge protection test were assessed in piglets. The results showed that both the S protein and the protein mixture induced the production of high levels of specific IgG antibodies and neutralizing antibodies and effectively neutralized PDCoV-infected LLC-PK cells in vitro. Furthermore, compared with the S protein, the N and M proteins in the protein mixture promoted the expression of CD8+ T cells and IFN-γ, induced a stronger cellular immune response, and effectively protected 4/5 of the piglets from PDCoV infection. In conclusion, the results of this study showed that the N and M proteins play important roles in inducing an immunoprotective response. Using N and M antigens as effective antigenic components in the development of PDCoV vaccines in the future will effectively increase the immune efficacy of the vaccines.

Elucidating the biological characteristics and pathogenicity of the highly virulent G2a porcine epidemic diarrhea virus

Since the large-scale outbreak of porcine epidemic diarrhoea (PED) in 2010, caused by the genotype 2 (G2) variant of the porcine epidemic diarrhoea virus (PEDV), pig farms in China, even those vaccinated with the G2b vaccine, have experienced infections from the G2a variant, leading to significant economic losses. This study successfully isolated the G2a strain DY2020 from positive small intestine contents (SICs) by blind passage on Vero cells for four generations. The SICs were taken from Daye, Hubei Province, China. The biological characteristics were identified by indirect immunofluorescence assay (IFA) and transmission electron microscopy (TEM). The growth kinetics of the strain on Vero cells were detected by TCID50, and the virus titre could reach 107.35 TCID50 ml-1 (SD: 5.07×106). The pathogenicity towards colostrum-deprived piglets was conducted by assessing faecal viral shedding, morphometric analysis of intestinal lesions, and immunohistochemical staining. The results showed that DY2020 was highly virulent to colostrum-deprived piglets, with severe watery diarrhoea and other clinical symptoms appeared at 6 h post-infection (h p.i.), and all died within 30 h. Pathological tissue examination results showed that the lesions mainly occurred in the intestines of piglets, causing pathological changes such as shortening of intestinal villi. In summary, the discovery of the G2a strain DY2020 in this study is of great significance for understanding Hubei PEDV and provides an important theoretical basis for the development of new efficient PEDV vaccines.

Prevention and Control of Swine Enteric Coronaviruses in China: A Review of Vaccine Development and Application

Swine enteric coronaviruses (SECs) cause significant economic losses to the pig industry in China. Although many commercialized vaccines against transmissible gastroenteritis virus (TGEV) and porcine epidemic diarrhea virus (PEDV) are available, viruses are still widespread. The recent emergence of porcine deltacoronavirus (PDCoV) and swine acute diarrhea syndrome coronavirus (SADS-CoV), for which no vaccines are available, increases the disease burden. In this review, we first introduced the genomic organization and epidemiology of SECs in China. Then, we discussed the current vaccine development and application in China, aiming to provide suggestions for better prevention and control of SECs in China and other countries.