PEDV S基因变异与仔猪发病及免疫差异相关性研究

Porcine epidemic diarrhea virus mainly causes severe diarrhea, vomiting, dehydration, and death in piglets, and the mortality of newborn piglets can reach to 100%. PEDV have two genotypes: G1 and G2. Before 2010, the prevalence of PEDV was G1 genotype, after 2010, it was G2 genotype. The G1 genotype vaccine developed in China control the prevalence of PEDV effectively. However, since the late 2010, a remarkable increase in PEDV outbreaks and prevalence in global, bring economic loss for the pig industry, which suggested that the PEDV G1 vaccine could not provide completely protection to G2 viruses. Research showed that gene variation emerged in the PEDV genome, and the variation mainly happened in the S gene. Did the pathogenicity of PEDV G2 enhanced after the S gene variation? And the molecular mechanism of that the neutralizing antibody induced by the PEDV G1 vaccine could not neutralize the G2 viruses completely still need to research. Based on these question, this study will confirm the pathogenicity difference of PEDV G1 and G2 for piglets by animal infection experiments; and study the cross protection of G1 and G2 as vaccine, respectively; as well as study the molecular mechanism that G1 vaccine could not provide completely protection to G2 genotype. This study will provide useful knowledge for control the prevalence of PEDV.

猪流行性腹泻病毒（PEDV）主要引起仔猪急性腹泻、呕吐、脱水和死亡，对幼龄仔猪的致死率高达100%。PEDV分为G1和G2亚型。2010年之前，流行毒株以G1亚型为主，2010年之后以G2亚型为主。我国研制的PEDV G1疫苗，有效控制了PEDV流行，但自2010年后期PEDV广泛流行，随后遍及全球给养猪业带来重大经济损失，表明G1型疫苗不能对G2型毒株提供完全保护。研究发现PEDV基因组发生变异，差异主要在S基因。S基因变异后PEDV G2与G1毒株相比对仔猪的致病力是否增强？PEDV G1疫苗诱导的抗体不能完全中和PEDV G2的分子机制是什么？针对上述问题，本项目通过动物感染实验验证PEDV G1和G2亚型毒株对仔猪致病性差异，研究G1和G2毒株分别作为疫苗株的交叉免疫保护能力及其不能形成完全保护的分子机制，以期为防控PEDV流行提供科学依据。

猪流行性腹泻病毒（PEDV）主要引起仔猪急性腹泻、呕吐、脱水和死亡，对幼龄仔猪的致死率高达100%。PEDV分为G1和G2亚型。2010年之前，流行毒株以G1亚型为主，2010年之后以G2亚型为主。我国研制的PEDV G1疫苗，有效控制了PEDV流行，但自2010年后期PEDV广泛流行，随后遍及全球给养猪业带来重大经济损失，表明G1型疫苗不能对G2型毒株提供完全保护。研究发现PEDV基因组发生变异，差异主要在S基因。S基因变异后PEDV G2与G1毒株相比对仔猪的致病力是否增强？PEDV G1疫苗诱导的抗体不能完全中和PEDV G2的分子机制是什么？针对上述问题，本项目通过动物感染实验验证PEDV G1和G2亚型毒株对仔猪致病性差异以及G1和G2毒株分别作为疫苗株的交叉免疫保护能力及其免疫原性差异的分子机制。实验结果证实：PEDV G1（CH/S）和G2（LNCT2）对仔猪的致病性无显著差异，1-5日龄仔猪感染PEDV后最快17个小时即可出现呕吐、腹泻症状；PEDV G1（CH/S）和G2（LNCT2）主要感染仔猪空肠和回肠。交叉免疫保护实验证明：PEDV G1（CV777）毒株免疫母猪的产生的猪奶能完全保护仔猪经受G2（LNCT2）毒株的攻击；PEDV G2（LNCT2）毒株免疫母猪的产生的猪奶能完全保护仔猪经受G1（CH/S）毒株的攻击；采集的母猪初乳分别纯化出SIgA和IgG抗体，检测SIgA和IgG抗体中和病毒的差异表明：CV777诱导的SIgA抗体中和LNCT2毒株的能力与LNCT2诱导的SIgA抗体中和CV777毒株的能力无显著差异；但CV777诱导的IgG抗体中和LNCT2毒株的能力比LNCT2诱导的IgG抗体中和CV777毒株的能力要弱。IFA检测两种毒株诱导的SIgA抗体效价无显著差异。通过筛选PEDV S蛋白诱导产生的中和性单克隆抗体证实PEDV不同毒株免疫原性差异主要是由S基因S1部分的变异决定的。本项目的实施阐明了PEDV G1和G2亚型毒株对仔猪无致病性差异，G1和G2毒株分别作为疫苗株可具备良好的交叉免疫保护能力；揭示了S基因变异能够引起免疫原性差异。因此，揭示接种PEDV疫苗的猪场仍发生PEDV引起的腹泻的原因，有必要对其它引起免疫抑制的病原展开研究，以期防控好PEDV引起的仔猪腹泻。