Spatial and stochastic simulation to evaluate the impact of events and control measures on the 1997-1998 classical swine fever epidemic in The Netherlands. II. Comparison of control strategies

Using the spatial, temporal and stochastic simulation model InterCSF, several alternative pre-emptive slaughter strategies that could have been applied in the Dutch Classical Swine Fever (CSF) epidemic of 1997–1998 were evaluated. Furthermore, effects of changes in some disease-spread and disease-control parameters were studied. InterCSF simulates the spread of CSF between farms through local spread and contacts (animals, transport and persons). Disease spread is affected by control measures implemented through different mechanisms (e.g. depopulation of infected farms, pre-emptive slaughter, movement control). The starting point for the evaluation of strategies was a simulated basic scenario, which mimicked the real epidemic. Strategies were compared using epidemiological as well as economic results. Economic results were generated by a separate model (EpiLoss) that calculated the direct losses and consequential losses for farmers and related industries. The comparison of the different alternatives to the basic scenario led to some general conclusions on the Dutch CSF-epidemic. Pre-emptive slaughter seemed to be an effective strategy to reduce the size of an epidemic, if started at an early stage. Economically, pre-emptive slaughter was not as expensive as expected; the resulting smaller size of the epidemic, combined with less welfare slaughter, led to much lower overall losses. Furthermore, although large movement control areas seemed effective in reducing the size of the epidemic, the total losses were relatively high because of subsequent welfare slaughter. If infection probabilities could be reduced, for example by improved biosecurity, the resulting epidemics would be much smaller.     

Spatial and stochastic simulation to evaluate the impact of events and control measures on the 1997-1998 classical swine fever epidemic in The Netherlands. I. Description of simulation model

The simulation model InterCSF was developed to simulate the Dutch Classical Swine Fever (CSF) epidemic of 1997–98 as closely as possible. InterCSF is a spatial, temporal and stochastic simulation model. The outcomes of the various replications give an estimate of the variation in size and duration of possible CSF-epidemics. InterCSF simulates disease spread from an infected farm to other farms through three contact types (animals, vehicles, persons) and through local spread up to a specified distance. The main disease-control mechanisms that influence the disease spread in InterCSF are diagnosis of the infected farms, depopulation of infected farms, movement-control areas, tracing, and pre-emptive slaughter. InterCSF was developed using InterSpread as the basis. InterSpread was developed for foot-and-mouth disease (FMD). This paper describes the process of modifying InterSpread into InterCSF. This involved changing the assumptions and mechanisms for disease spread from FMD to CSF. In addition, CSF-specific control measures based on the standard European Union (EU) regulations were included, as well as additional control measures that were applied during the Dutch epidemic. To adapt InterCSF as closely as possible to the Dutch 1997/98 epidemic, data from the real epidemic were analysed. Both disease spread and disease-control parameters were thus specifically based on the real epidemic. In general, InterSpread turned out to be a flexible tool that could be adapted to simulate another disease with relative ease. The most difficult were the modifications necessary to mimic the real epidemic as closely as possible. The model was well able to simulate an epidemic with a similar pattern over time for number of detected farms as the real outbreak; but the absolute numbers were (despite many relevant modifications) not exactly the same — but were within an acceptable range. Furthermore, the development of InterCSF provided the researchers with a better insight into the existing knowledge gaps. In part II (see the final paper in this issue), InterCSF was used to compare various control strategies as applied to this epidemic.     

混合感染猪繁殖与呼吸综合征和圆环病毒2型猪群的猪瘟抗体变化研究

本试验研究旨在探究猪场发生猪繁殖与呼吸综合征(PRRS)与圆环病毒2型(PCV2)混合感染后,猪群的猪瘟抗体变化,运用RT-PCR、实时荧光RT-PCR与PCR方法,对四川某规模化发病猪场进行高致病性PRRS、猪瘟与圆环2型的病原检测。结果显示高致病性PRRS、圆环2型和猪瘟阳性率分别为54%(19/35)、50%(17/34)、0(0/5)。结合临床症状、病猪剖检变化,确诊为PRRSV与PCV-2混合感染。采集PRRS与PCV-2混合感染病猪血清12份为试验组,本场健康猪只(无临床症状、抗原检测阴性)12份为对照组,运用ELISA试验检测猪群猪瘟抗体,结果显示试验组的猪瘟抗体合格率为33%(4/12),显著低于健康对照组的合格率83.3%(10/12)(P0.05),结果表明PRRS和PCV2混合感染会对猪瘟抗体产生负面影响。     

猪瘟活疫苗(细胞源)两种免疫剂量的使用效果对比

根据基层实际情况,选取2种免疫剂量(1头份和6头份)的政府采购猪瘟活疫苗(细胞源),接种6个场的试验猪。比较免疫后不同时间的抗体合格率,结果显示2种免疫剂量的政府采购猪瘟活疫苗在一免后(40-50日龄)抗体水平较低,二免后(81日龄)抗体水平显著提高,均达到全群保护的合格率,且2种免疫剂量无差别。1头份免疫剂量能获得良好的免疫效果。     

某猪场猪瘟病例的综合诊断及病原基因分析

2017年3月山东省莱芜市某猪场保育猪群发生以高热(40.8~41.5℃)、精神高度沉郁、食欲不振、皮肤出血潮红及耳尖发绀为主要症状的急性热性传染病。为明确引起此次疫情的致病因素,对患病猪进行了病理剖检、组织病理学检查、分子生物学检测、病毒分离与鉴定,对分离病毒进行了E2基因的分子克隆测序及同源性比对,最终确定该病由猪瘟病毒感染引起,并分离到1株猪瘟病毒(SDLW2017)。该病毒株E2基因全长1119个碱基(nt),共编码373个氨基酸(aa);相似性分析表明,SDLW2017分离株与其它参考株的核苷酸相似性介于82.1%~96.3%,氨基酸相似性介于88.5%~97.6%,与1.1亚群HCLV株的核苷酸和氨基酸相似性最低,分别为82.1%和88.5%,而与2.1亚群参考株的核苷酸和氨基酸相似性较高,分别为91.8%~96.3%和95.2%~97.6%,其中与2.1b亚型参考株(GXWZ02)的相似性最高,分别为96.3%和97.6%。     

一起仔猪注射猪瘟、猪丹毒、猪肺疫三联灭活苗引起的过敏反应

猪瘟、猪丹毒、猪肺疫三联灭活苗(以下简称猪三联)是防疫工作中常用的疫苗，一般情况下注射后反应轻微，有严重过敏反应者并不多见。笔者在工作中曾遇到一起因注射猪三联引发严重过敏反应的病例。现介绍如下：     

一起猪瘟病毒和副猪嗜血杆菌混合感染病例的诊断

四川遂宁某养猪场送检病猪2只,通过临床解剖、细菌分离鉴定、PCR、RT-PCR等方法进行实验室诊断,综合判定为猪瘟和副猪嗜血杆菌混合感染,并从发病猪体内成功分离到一株副猪嗜血杆菌.采用K-b法检测副猪嗜血杆菌分离菌株对28种常用抗菌药的敏感性,结果显示,该菌株耐药性比较严重,仅对复达欣、头孢肤肟、左旋氧氟沙星敏感.     

仔猪非典型性猪瘟混合感染水肿病的诊断与防治

猪瘟是一种急性、热性和高度接触性的病毒性传染病,其特征为发病急、高热稽留和细小血管壁变性,引起全身泛发性小点出血、脾梗死。急性猪瘟由强毒引起,发病率和死亡率高。自1955年我国研制成功猪瘟     

广西一株流行猪瘟毒株全基因序列的克隆和序列分析

本实验参照已发表的猪瘟病毒(CSFV)石门株、HCLV株、Paderborn株、GXWZ02株等的基因组序列设计合成了11对引物,通过RT-PCR方法从广西一株流行猪瘟病料中直接扩增得到了11个片段,将所得片段克隆至PGEM-Teasy载体上,经过测序、拼接,最终得到广西猪瘟GX54基因组全序列。序列分析表明,GX54基因组全长12296个碱基。与国内外已发表的10株猪瘟病毒系列进行同源性分析,结果表明,与各株核苷酸同源性分别为85.1%、85.0%、85.1%、84.7%、84.8%、94.4%、84.3%、94.3%、84.8%、84.5%。系统发育树分析发现,所比较的11个毒株可以分为2群,1群包括GX54,GXWZ02和Paderborn株,其余毒株属于2群,其中GX54株与GXWZ02株关系最近。     

一起注苗猪发生猪瘟的诊断与防制

猪瘟是严重危害养猪业的传染病，传染和死亡率较高。多年来，我们在认真贯彻综合性防制措施的基础上，重点抓住预防接种，使猪瘟的发病率及死亡率显著下降。然而在高密度免疫的情况下，猪瘟时有发生。笔者现将亲自诊断处理的一起注苗猪发生猪瘟的情况报道如下。１流行病学调查此次疫情发生于武威市某个体养猪专业户，共饲养猪２３０头。于１９９９年５月３日从四川内江购进一月龄仔猪１５０头，引进第２ｄ，曾请当地兽防所的兽医购进仔猪接种猪瘟兔化弱毒苗（兰州生药厂生产）。接种后到６月２日，猪群出现低热、腹泻、便秘、不食等症状。用…     

The 1997/1998 epizootic of swine fever in the Netherlands: control strategies under a non-vaccination regimen

The 1997/1998 epizootic of classical swine fever (CSF) in an area with high pig density in the Netherlands is described. The epizootic, which numbered 429 outbreaks, was controlled and finally eradicated after 14 months without resorting to vaccination. A further almost 1300 herds (1.1 million pigs) at close proximity of confirmed outbreaks were preventively culled because of the risk of having been infected. The pros and cons of this so-called "pre-emptive slaughter" are discussed.The long-lasting movement restrictions caused severe overcrowding especially in breeding farms. For reasons of animal welfare 6.5 million weaners and adult pigs had to be killed and destroyed, whereas another 2.6 million 3-17 days old piglets were euthanised to save long-term destruction capacity. The presumed routes of infection and factors influencing the epizootic are explained, as well as the various methods to bring the epizootic to a halt. The strategy for detecting outbreaks in an early stage, and the type of samples to be collected for laboratory diagnosis are emphasised from the general point of application. The direct costs of the epizootic, losses of exports not included, are estimated at US$ 2 billion.     

Classical swine fever in The Netherlands 1997-1998: a description of organisation and measures to eradicate the disease

The central and regional organisation of the campaign to eradicate the CSF epidemic in the Netherlands in 1997/1998 is described. The main instruments used in the campaign were based on stamping-out and movement restrictions specified by the European Union. Additional instruments were used for the first time, namely, pre-emptive culling of contact and neighbouring farms, compartmentalisation of transport, monthly serological screening in established surveillance areas and supervised repopulation of all farms in the former surveillance zone. Two other measures, the killing of very young piglets and a breeding ban were introduced to reduce production in established surveillance zones. Several factors complicated the eradication campaign, for instance, the late detection of the first infection; artificial insemination as a source of infection; the organisation of pig farming in the Netherlands, with its highly concentrated production and dependence on the transport of stock from one unit to another; insufficient rendering capacity; decreasing sensitivity of clinical inspection; and extremely high costs.     

我国猪瘟流行新特点与疫苗免疫研究

对我国的猪瘟流行的新特点进行了描述,详细分析了造成猪瘟疫苗免疫失败的6大原因,并且对疫苗的发展历史和研究进展进行了详细介绍,提出了猪瘟防控的两个关键环节为种猪群野毒感染的控制及有效的免疫接种。     

百色市屠宰猪和市场销售仔猪猪瘟抗体监测报告

为了切实提高猪瘟等动物疫病的免疫密度，我们在全市范围内开展拉网式的免疫工作，做到“县不漏乡、乡不漏村、村不漏屯、屯不漏户、户不漏畜、畜不漏针”的防疫工作措施，切底消灭免疫空白村屯和免疫死角，使猪瘟免疫密度达到新高。2004年全市饲养牲猪396．1万头，共免疫注射猪瘟疫苗362．45万头，免疫率达91．52％。为了进一步掌握我市牲猪猪瘟的免疫质量与效果，2004年11～12月份我们对全市12个县区621份屠宰猪血清和9个县区84份仔猪血清进行猪瘟抗体监测，现将情况报告如下。     

某规模化猪场猪瘟和伪狂犬病净化的实施及成效分析

针对当前规模化猪场猪瘟病毒及伪狂犬病病毒感染的严峻状况,选取山东省某规模化猪场核心种猪群开展猪瘟及伪狂犬病的净化工作。结合血清学、分子生物学诊断方法,在系统研究了该场两种疫病的流行病学、带毒状况及疫苗免疫状态的基础上,对种猪群进行为期约一年的猪瘟及伪狂犬病净化工作,在良好的卫生防疫措施的基础上,精选疫苗、制定合理的免疫程序,淘汰带毒猪及抗体阴性猪。结果显示:经过两次净化,种猪群的猪瘟病毒带毒率下降到3.03%,伪狂犬病病毒带毒率下降到3.23%,生产成绩得到明显改善,达到了净化之目的。     

某猪场猪瘟抗体水平检测及反思

近年来各养殖场重视疫病防控工作,尤其是疫苗免疫接种。某猪场对饲养的猪针对8种疾病用6种疫苗进行免疫接种。结果是急性暴发性典型性疫病越来越少,而慢性非典型性疫病在不断增多,以猪瘟为例,猪场管理者认为猪瘟免疫从未有半点懈怠,却每年都有慢性猪瘟发生,为了了解和掌握该猪场的猪瘟免疫后抗体产生情况,笔者对该场不同年龄的猪采血,用正向间接血凝方法检测猪瘟抗体,结果表明1岁以上的母猪抗体水平较高,3月龄以下的猪抗体水平非常低,这是免疫时机掌握不当,还是另有原因正是我们关注的。1材料与方法1.1被检材料:耳静脉采猪血,分离血清,低温…     

Molecular epidemiology of a large classical swine fever epidemic in the European Union in 1997-1998

A big epidemic of classical swine fever (CSF) occurred in the European Community in 1997. The first case was reported at the beginning of January 1997 from Germany. The disease presumably spread to the Netherlands, and from there to Italy, Spain and eventually to Belgium. About 30 isolates from these outbreaks were analysed by comparison of the nucleotide sequence data generated from fragments of both the E2 glycoprotein gene (190 nucleotides) and from the 5'-nontranslated region (5'-NTR; 150 nucleotides). By combining epidemiological data with genetic typing, it was found that the outbreaks were related and caused by a virus belonging to the genetic subgroup 2.1. As this type of virus had been reported infrequently in Europe and not at all since 1993, we postulate that it was newly introduced into the European Union (EU).     

青岛市某猪场猪瘟的发生、诊断与防治报告

青岛某大型养猪场地处城阳区，饲养有杜洛克、长白等优良品种。饲养种母猪600多头，种公猪13头，全部采用人工授精配种。母猪平均每胎产仔数为9．75头。现存栏种公猪、母猪、仔猪、育成和育肥猪共有6500多头。全部采取自繁自养的方式。种母猪免疫过猪瘟、蓝耳病(PRRS)和伪狂犬病的二联灭活疫苗及细小病毒灭活疫苗。该场母猪免疫程序是：配种前一个月免疫4倍量猪瘟冻干苗，母猪产后在仔猪断奶前后进行猪瘟窝防(仔猪和母猪同时免疫)。     

广西猪瘟病毒E0和E2基因的克隆及序列分析

通过分析目前广西猪瘟病毒(CSFV)的E0和E2基因特征,为了解广西地区CSFV的分子流行病学、遗传变异及综合防控提供科学依据。试验采用RT-PCR方法,对阳性猪瘟样品进行CSFV的E0及E2基因的扩增,经克隆、测序后,利用DNAStar软件对序列进行比对分析,同时绘制系统遗传进化树。结果表明,从阳性猪瘟样品中成功扩增CSFV的E0及E2基因。序列比对分析发现,GX2毒株与参考毒株的E0基因核苷酸同源性在83.1%~94.1%,其推导氨基酸同源性在85.9%~99.6%;与参考毒株的E2基因核苷酸同源性为81.7%~93.7%,其推导氨基酸同源性为89.0%~97.0%;E0与E2基因均属于基因Ⅱ群。氨基酸变异位点分析表明,E0蛋白的RNase活性区域氨基酸基序位点没有发生变异;E2蛋白中15个位点上的半胱氨酸均未发生变异,但单抗识别位点S734R发生变异。遗传进化分析显示测定的GX2毒株与近年来广西CSFV流行毒株的变异趋势相似,与中国传统疫苗株HCLV、经典强毒株Shimen的同源性较低,亲缘关系较远,与广西近年来的流行毒株GXWZ02株的同源性较高,亲缘关系较近。