A Highly Pathogenic Strain of Porcine Deltacoronavirus Caused Watery Diarrhea in Newborn Piglets

Porcine deltacoronavirus(PDCoV) is a newly identified virus that causes watery diarrhea in newborn piglets and results in significant economic losses to the pig industry. Since first reported in Hong Kong in 2012, PDCoV has been subsequently detected in USA, South Korea, Thailand, and China's Mainland. Here we isolated a strain of PDCoV, named CHN-GD-2016,from the intestinal content of a diseased newborn piglet with severe diarrhea in a pig farm in Guangdong, China. PDCoV CHN-GD-2016 could be identified by immunofluorescence with PDCoV specific rabbit antisera, and typical crown-shaped particles with spiky surface projections of this PDCoV were observed with electron microscopy. Genomic analysis showed that the PDCoV CHN-GD-2016 was closely related to other Chinese PDCoV strains, with the highest sequence similarity with the strain CHN/Tianjin/2016. Importantly, inoculation of newborn piglets with 1×10~5 TCID_(50) of CHN-GD-2016 by oral feeding successfully reproduced clear clinical symptoms, including vomiting, dehydration, and severe diarrhea in piglets. In addition, the virus RNA in rectal swabs from 1 to 7 days post inoculation was detected, macroscopic and microscopic lesions in small intestine were observed, and viral antigen was also detected in the small intestines with immunohistochemical staining. Collectively, the data show in this study confirms that PDCoV is present in Guangdong,China and is highly pathogenic in newborn piglets.

猪德尔塔冠状病毒双脯氨酸突变S蛋白的表达及免疫原性评价

【目的】猪德尔塔冠状病毒(porcine deltacoronavirus,PDCoV)是一种重要的猪肠道冠状病毒,给全球生猪养殖业带来了巨大的经济损失,截至目前,尚无可用的商品化疫苗。本研究选择宿主免疫反应主要诱因因子棘突(spike,S)蛋白,并将PDCoV S蛋白七肽重复序列1(heptapeptide repeat-1,HR1)与中心螺旋之间的环中855和856位点均突变为双脯氨酸(E855P和V856P),然后利用ExpiCHO-S真核表达系统表达、纯化重组S蛋白和双脯氨酸突变S蛋白(S2P)并评价其免疫原性及免疫保护性,以初步研制一种免疫效果较好的PDCoV亚单位疫苗。【方法】利用间接酶联免疫吸附法检测免疫小鼠血清特异性抗体IgG水平;利用血清中和试验检测免疫小鼠血清中和抗体滴度;通过流式细胞术检测免疫小鼠T淋巴细胞增殖情况;通过细胞因子检测免疫小鼠干扰素(interferon,IFN)-γ、IFN-α、白细胞介素(interleukin,IL)-2和IL-4等细胞因子分泌情况;采用RT-qPCR检测攻毒后小鼠肠道组织PDCoV病毒载量;采用病理组织切片检测小鼠肠道有无病理损伤;利用免疫组织化学检测小鼠肠道组织PDCoV抗原分布情况。【结果】免疫原性结果显示,小鼠在肌肉注射S组和S2P组亚单位疫苗后能够产生较高水平的抗PDCoV特异性IgG抗体,免疫后42 d的小鼠血清均对PDCoV具有中和作用,其中,S2P组对LLC-PK细胞50%中和保护效价显著高于S组。此外,S组和S2P组显著地诱导小鼠CD_(4)^(+)T淋巴细胞增殖,并且S2P组高于S组,而S2P组能够诱导小鼠CD_(8)^(+)T淋巴细胞增殖,但S组与PBS组并无差异。同时,S组和S2P组诱导的IFN-γ、IFN-α、IL-2和IL-4等细胞因子水平均显著高于PBS组,但S组和S2P组并无差异。免疫保护性结果显示,PBS组肠组织中可检测到PDCoV病毒,肠组织出现病理损伤且可见大量PDCoV抗原,而S组和S2P组未检测到PDCoV病毒且未观察到肠组织损伤,二者之间无明显差异。【结论】S2P组较之S组能够诱导小鼠产生更高水平的抗PDCoV体液免疫应答,两组疫苗对小鼠均有一定的保护效果,本研究为后续PDCoV亚单位疫苗研发奠定坚实的基础。