摘要
2019年8月首次在我国新疆伊犁暴发牛结节性皮肤病,随后传至全国各地。由于对这一新发病缺少全面认识和防控经验,临床上所用措施常表现出缺少针对性,导致该病的蔓延,给养牛业造成了重大经济损失。为明确该病发生的关键风险因素和防控该病的关键环节,本文从病原学特征、致病机制、临床特征、传播规律、诊断、预防和综合防控措施等方面进行了系统阐述,并针对我国牛结节性皮肤病的有效防控和净化提出了建议。
牛结节性皮肤病(lumpy skin disease,LSD)是由牛结节性皮肤病病毒(lumpy skin disease virus,LSDV)引起的一种牛的重要传染病,世界动物卫生组织(World Organisation for Animal Health,WOAH)将其列入必须通报疫病名
由于缺少对该新发传染病的全面了解和防控经验,临床上常表现出不知所措或所用措施缺少针对性,这是导致该病迅速蔓延的重要原因。因此,本文从病原学特征、致病机制、临床特征、传播规律、诊断、预防和综合防控措施等方面对该病的基本特征和最新研究进展进行系统介绍,旨在阐明该病发生的关键风险因素和防控该病的关键环节,进一步提出防控建议,以期为我国LSD有效预防、控制和净化提供参考。
LSD于1929年在赞比亚首次报道,已在撒哈拉沙漠以南地区持续流行50多年。1988年后,传至撒哈拉沙漠以北地区,并在非洲大陆蔓
LSD始于非洲,经过欧洲,近年来在亚洲广泛流行(数据来源:FAO,https://empres-i.fao.org)。截至2021年12月,已有75个国家和地区(其中包括中国香港和中国台湾地区)向WOAH报告LSD疫情(

图1 全球LSD疫情在非洲、欧洲和亚洲的时间分布图
Fig. 1 Temporal distribution of global LSD outbreaks in Africa,Europe and Asia
数据来源:WOAH世界动物健康信息系统 Data source:WOAH. http://wahis.woah.int/#/home.
溯源研究表明,2019年7月孟加拉国通报出现有关牛科动物感染LSD的疫情,其病毒株与肯尼亚分离株(Kenyan NI-2490/Kenya/KSGP-like field)的基因序列相似性很
我国首次LSD疫情发生于2019年8月的新疆伊犁哈萨克自治州。该疫点距离哈萨克斯坦边境仅60 km,位于河谷虫媒密集地区。对LSDV全基因组分析可知,新疆毒株为Xinjiang/2019株(Xinjiang/2019),该毒株与2017年在俄罗斯分离的疫苗毒、野毒重组病毒株LSDV/Russia/Saratov/2017(MH646674.1)有着密切的亲缘关系,相似性高达99.4%,说明我国LSD疫情是输入性
此后,LSD疫情在距离我国首次疫情点约4 800 km的福建再次报道,相继在我国14个省份报道发生(

图2 我国2020-2021年LSD发病情况
Fig. 2 Number of LSD cases outbreaks in cattle in China from 2020-2021
A:2020年我国牛结节皮肤病发病情况;B:2021年我国牛结节皮肤病发病情况,数据来源:农业农村部《兽医公报》。A:Number of LSD cases outbreaks in
LSDV属于痘病毒科(Poxviridae)山羊痘病毒属(Capripoxvirus,CaPV),是一种双股DNA病毒,具有囊膜,基因组较大,包含156个假定基
按照文献[
临床上,LSD以全身皮肤表面产生广泛性结节为主要特征。结节直径为5~50 mm,坚硬,呈平顶丘疹状,可深入至皮下层直至肌
感染LSDV的牛可能成为无症状带毒者。据报道,LSDV经静脉和皮内注射2种途径人工感染牛体后,只有37.5%的犊牛出现全身皮肤结节症状,另62.5%的接种犊牛表现亚临床症状,无皮肤结节,但全血中可能携带病毒核酸,但载毒量低于具有临床症状的牛,全血与皮肤组织中的载毒量变化规律相
LSDV可侵染体内多个器官和组织。病理解剖可见口腔、鼻腔、角膜、胃和气管等部位黏膜表面出现结节,严重者几乎所有内脏器官表面都可能有结节。淋巴结肿大,伴有出血。心、肺和脾等各脏器肿大,充血或出血,胃和小肠黏膜出
LSDV可通过吸血虫媒间接传播或通过与病牛直接接触传播。病牛体表和黏膜面的结节破溃部位含有大量病毒,牛只相互舔舐是主要的直接传播方式。带毒牛或其产品的长途运输可导致LSDV的远程传播。LSDV也可经胎盘、精液、受污染饲料、水、设备和兽医注射用的针头等传
了解致病机制是开展有效防控措施的基础。然而痘病毒科成员多,编码基因多且注释不全,其致病和免疫逃避机制远未完全弄清楚,LSDV的致病机制研究基本处于空白。
痘病毒末端重复序列基因可编码一些结构上类似细胞因子或细胞因子受体等免疫相关分子,通过竞争性结合其配体抑制宿主免疫反
痘病毒科成员通过多种途径抑制宿主细胞转录因子的激活。羊口疮病毒的ORFV121蛋白和痘苗病毒的N1L蛋白可抑制NF-κB分子激
痘病毒可通过诱导或抑制宿主细胞凋亡发挥致病作
LSDV ORF005编码IL-10类似分
基因名称 Gene name | 病毒名称 Virus name | LSDV同源基因 LSDV homologous genes | 基因功能描述 Gene function description |
---|---|---|---|
A52R | 痘苗病毒 Vaccinia virus | LSDV150 | 假定蛋白 Hypothetical protein |
B15R | 痘苗病毒 Vaccinia virus | LSDV001/LSDV156 | 假定蛋白 Hypothetical protein |
M131R | 黏液瘤病毒 Myxomatosis virus | LSDV131 | 超氧化物歧化样蛋白 Superoxide dismutase-like protein |
N1L | 痘苗病毒 Vaccinia virus | LSDV142 | 推测分泌毒力因子 Putative secreted virulence factor |
OVIFNR | 羊口疮病毒 Orf virus | LSDV014 | 抑制蛋白激酶PKR Inhibit protein kinase PKR |
vIL-10 | 羊口疮病毒 Orf virus | LSDV005 | IL-10样蛋白 Interleukin-10-like protein |
结合临床症状(牛的皮肤或黏膜表面出现广泛性结节)和流行病学特征(夏季发病和新引入牛等),可对牛结节性皮肤病作出初步诊断。确诊必须开展实验室诊断。发病牛的皮肤结节块、鼻腔分泌物、唾液、血液等样本均可用于实验室诊断。
WOAH认可的实验室方法包括病原检测方法和免疫学检测方法。前者包括病毒分离、使用实时荧光定量PCR,传统PCR检测核酸和电镜观察病毒粒子等;而后者包括中和试验(VNT)、间接免疫荧光试验(IFAT)和酶联免疫吸附试验(ELISA)等。不同的诊断方法服务于不同用途,因此,应根据检测目的选用合适的检测方法(
检测目的 Purposes | 检测病原因子 Detection of the agent | 检测免疫反应 Detection of immune response | ||||
---|---|---|---|---|---|---|
病毒分离Virus isolation | 聚合酶链反应 PCR | 透射电镜 TEM | 中和试验 VNT | 间接免疫荧光 IFAT | 酶联免疫 吸附法 ELISA | |
群体无疫检测Population freedom from infection | + | ++ | - | ++ | + | ++ |
个体移动前无疫检测Individual animal freedom from infection prior to movement | ++ | +++ | - | ++ | + | ++ |
用于根除政策 Contribute to eradication policies | + | ++ | - | ++ | + | ++ |
临床病例确诊 Confirmation of clinical cases | +++ | +++ | + | ++ | + | ++ |
流行率监测 Prevalence of infection-surveillance | + | + | - | ++ | + | ++ |
免疫后个体或群体免疫状态检测 Immune status in individual animals or populations post-vaccination | - | - | - | ++ | + | ++ |
注: +++:推荐使用于该目的;++:推荐但有一定局限性;+:在极有限条件下适用;-:不适合用于该目的。Note:+++:Recommended for this purpose; ++:Recommended but has limitations; +:Suitable in a few circumstances; –:Not appropriate for this purpose.
接种疫苗是控制LSD有效的办法。LSD的免疫保护主要与细胞免疫相关,中和抗体效价与免疫保护间没有明确的对应关
LSD疫苗株与野毒株之间的重组可能成为引发新疫情的风险因素之
我国目前采取羊用山羊痘减毒活疫苗(AV41株)预防牛LSD,使用5头份的羊剂量进行皮内接
牛体接种疫苗免疫后10~15 d,血清抗体反应可能转阳;30 d左右达到高峰随后会逐渐下降,但同时不是所有接种牛都产生较高水平的抗体反
在全球经济一体化和全球命运共同体理念的倡导下,国内外的牛业贸易往来日益频繁,LSD的潜在传播风险也随之扩大。虫媒参与传播LSD,使得控制和净化更加困难。建议从以下方面着手开展防控技术研究,提高综合防控水平。
1)加强LSDV致病和免疫机制研究,提高LSD防控技术水平。关于LSDV的致病机制和免疫机制研究很少,基本上不清楚。目前能肯定的是,弱毒力活疫苗的免疫保护效果较灭活疫苗好,但该病毒诱导免疫保护作用的组分并不清楚。基于已出现活疫苗毒株和野毒株间的重组病毒,活疫苗存在安全隐患。但要提高灭活疫苗的免疫保护效果,就必须弄清楚该病毒的免疫保护机制。同时,阐明LSDV致病机制也有助于发掘抗病毒疫苗、药物和诊断试剂靶标。如前所述,在已报道的17个毒力相关因子中,我们只在LSDV中发现6个同源基因,表明LSDV的致病机制具有独特性。此外,由于LSDV感染存在持续带毒状态,疫苗广泛免疫情况下,常用方法检测抗体难以区分疫苗免疫和自然感染,需要探索新的诊断靶标以建立区分疫苗免疫和自然感染的鉴别诊断技术。因此,有必要深入研究、解析LSDV的致病和免疫机制。
2)加强生物安全综合防控体系建设。牛的相关贸易往来频繁和季节性的虫媒活动是LSD传播的重要风险因子,因此必须从控制传染源、切断传播途径和保护易感动物3个环节入手建立生物安全综合防控体系,譬如牛群入场前需进行检测、隔离与免疫,有效降低LSDV引入的风
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