猪Deltacoronavirus RT-PCR检测方法的建立及其应用

猪Deltacoronavirus（PDCoV）是2014年在美国检测出的一种新型猪冠状病毒，能够引起感染猪出现水样腹泻、呕吐和脱水等症状。为及时评估该病毒在我国猪群中的感染和流行情况，本研究根据GenBank中登录的PDCoV核苷酸序列设计并合成一对特异性引物，在我国首次建立了PDCoV的RT．PCR检测方法。研究结果表明，所建立的RT．PCR检测方法仅对PDCoV核酸具有特异性扩增，对其它猪主要病毒核酸的扩增均呈阴性，具有较强的特异性；对PDCoV最低检测限为4．05×103拷贝／μL，敏感性较高；采用该方法对2014年～2015年我国华东地区猪场的526份临床样品进行检测，结果显示PDCoV总阳性率为4．75％（25／526），其中腹泻样品中阳性率为25．76％（17／66），表明我国猪群中存在PDCoV感染。本研究建立的RT—PCR方法可以作为临床检测PDCoV的一种有效手段。

Diversity of coronaviruses in wild and domestic birds in Vietnam

Objective:To investigate the genetic diversity of coronaviruses in wild and domestic birds in the bird park and live poultry markets of Ca Mau province in Vietnam in 2020.Methods:A total of 228 samples(121 from wild birds and 107 from poultry)were collected in the territory of Ca Mau province of Vietnam in 2020.The avian samples were tested for the presence of the four genera of coronaviruses using reverse transcription and nested PCR.Molecular genetic analysis using targeted NGS sequencing of RdRp gene was performed for 29 representative samples(12 samples from wild birds and 17 from poultry).Phylogenetic analysis was performed using the neighbour joininig method with 1000 bootstrap replications using MEGA X software.Results:Among wild birds,21.5%samples were positive for the genetic material of coronaviruses and 38.3%samples were positive for coronaviruses among poultry.Genetic analysis of the partial sequence of RdRp gene from representative samples revealed that wild birds were carriers of gammacoronaviruses and deltacoronaviruses.Among poultry,three genotypes of infectious bronchitis virus(QX,Mass and Q1)were detected in chickens,with QX genotypes being predominant,and viruses of DCoV group were detected in domestic ducks.There was no detection of alphacoronaviruses or betacoronaviruses in the studied birds.Conclusions:Coronaviruses of genera Gammacoronavirus and Deltacoronavirus were detected in wild birds.A high percentage of infectious bronchitis virus was detected in poultry.Thus,there is a need for broader surveillance of coronaviruses in birds,which can be used for evaluation of diversity,evolution and distribution of coronaviruses in Vietnam.Continuous surveillance of coronaviruses circulation in wild and domestic animals is necessary for implementing strategic measures for poultry and domestic animal protection and for evaluation of possible risk of circulating coronaviruses to human health.

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。