Evaluation of Cross-Protection between G1a- and G2a-Genotype Porcine Epidemic Diarrhea Viruses in Suckling Piglets

Abstract

To date, two genotypes, i.e., genotype 1 (G1) and genotype 2 (G2), of porcine epidemic diarrhea virus (PEDV) have been identified in swine, while the cross protection between the G2a and G1a subgenotypes is undetermined. Hence, in the present study, we attempted to observe a comparative pathogenicity and cross protection of G1a (CV777) and G2a (CH/JX/01) PEDVs. Initially pregnant sows were vaccinated twice with the two kinds of inactivated G1a- and G2a-based PEDV vaccines, respectively and the delivered neonatal piglets were challenged with prototype isolates of G1a and G2a PEDVs, and then the pathogenicity and cross-protection in neonatal piglets were observed. The results showed that CH/JX/01, a highly virulent and dominant G2a PEDV strain currently circulating in China had more severe pathogenicity in vitro and in vivo, and induced more strong immune responses, including higher titers of sIgA in maternal milk than that induced by CV777 PEDV, a prototype of G1a PEDV strain. All piglets from the sows immunized with CH/JX/01 could not only survive when challenged with the homologous PEDV, but also be fully protected when challenged with heterogenous G1a PEDV. In contrast, the piglets from the sows immunized with CV777 could be protected when challenged with homologous PEDV and only partially protected when challenged with heterologous G2a strain of PEDV (CH/JX/01). The findings of this study provide new insights into the pathogenicity, antigenicity, and immunogenicity of currently circulating wild type G2a PEDV, which might be valuable for the development of novel PEDV vaccine candidates with improved efficacy.

Keywords: Porcine epidemic diarrhea virus; cross-protection; diarrhea; immunogenicity; piglet.

Figure 1

Experimental design and sample collection. The top line indicates the day post porcine epidemic diarrhea virus (PEDV) challenge, the second line on the left indicates the gestation stage of sows, and the right line indicates the age of neonatal piglets.

Figure 2

The one-step growth curve of CH/JX/01 and CV777 in Vero-81 cells.

Figure 3

Indirect immunofluorescence assay to detect infection of PEDV strains CV777 and CH/JX/01 in Vero-81 cells.

Figure 4

Hemotoxylin and eosin-stained tissue sections of small intestine in piglets challenged by PEDV strains CV777 and/or CH/JX/01 (×100).

Figure 5

PEDV shedding patterns for all challenged piglets over time. For each group a line corresponds to the quantity of virus shed in rectal swabs for a single piglet from dpc 1 to dpc 7 is shown on the right side of the heatmap.

Figure 6

Group mean anti-PEDV sIgA response in maternal milk. Data presented as mean group ELISA sample-to-positive (S/P) ratios ± SEM. The significance level was set to ** indicates 0.001 < p ≤ 0.01, and *** indicates p ≤ 0.001.

Figure 7

Kaplan–Meier curves for mortality of piglets orally challenged by CV777 or CH/JX/01.

Figure 8

Levels of the cytokine Tumor necrosis factor-α (TNF-α) in all piglets at 48 and 96 hpc. The mortality of POS-2a was more than 40% in 96 hpc, the levels TNF-α were not detected; * indicates p < 0.05, ** indicates 0.001 < p ≤ 0.01, and *** indicates p ≤ 0.001.