Monte Carlo simulation of classical swine fever epidemics and control. I. General concepts and description of the model

A Monte Carlo simulation has been developed to describe the spread of classical swine fever virus between farms within a certain region. The data of the farms can be imported and considered individually. Transmission occurs via the infection routes direct animal and indirect person and vehicle contact, as well as by contaminated sperm and local spread. Parameters, such as incubation period and probability of detection, can be varied by the user and their impact on disease spread can be studied. The control measures stamping-out, movement control and pre-emptive slaughter in circular restriction areas as well as contact tracing can be applied and their effect on disease spread can thus be analysed. The numbers of culled and restricted farms and animals per epidemic and per day within an epidemic, the epidemic duration and the total length of restrictions per restricted farm are given. In an example, simulation runs were performed under the condition of application of all four-control measures. Because no real farm data were available, a test area was generated stochastically with a farm density of 1.3 farms/km(2). The distributions of the number of infected farms per epidemic and the epidemic length are shown.     

Risk factors for local spread of foot-and-mouth disease, 2010 epidemic in Japan

To provide a basis for effective foot-and-mouth disease (FMD) prevention measures, factors associated with local spread were investigated in this study using data of the 2010 FMD epidemic in Japan. Thirty-eight local clusters within a 500-m radius from source farms were selected. In the clusters with pig source farms, more neighboring farms were infected in a short time compared with the clusters with cattle source farms. The influence of distance and wind upon local spread did not show a significant difference between infected and noninfected neighboring farms. Large-size pig farms posed a greater risk of inducing local spread; the odds ratio with reference to small-size cattle farms was 16.73. Middle-size and large-size cattle farms had a greater risk of infection; odds ratios with reference to small-size cattle farms were 15.65 and 25.52, respectively. The present results are useful for understanding features of local spread and prioritizing farms for control measures.     

Simulation analyses to evaluate alternative control strategies for the 2002 foot-and-mouth disease outbreak in the Republic of Korea

Using the stochastic and spatial simulation model of between-farm spread of disease, InterSpread Plus, we evaluated the effect of alternative strategies for controlling the 2002 epidemic of foot-and-mouth disease (FMD) in the Republic of Korea. InterSpread Plus was parameterised to simulate epidemics of FMD in the population of farms containing susceptible animal species in the Korean counties of Yongin, Icheon, Pyongtaek, Anseong, Eumseong, Asan, Cheonan, and Jincheon. The starting point of our analyses was the simulation of a reference strategy, which approximated the real epidemic. The results of simulations of alternative epidemic-control strategies were compared with this reference strategy. Ring vaccination (when used with either limited or extended pre-emptive depopulation) reduced both the size and variability of the predicted number of infected farms. Reducing the time between disease incursion and commencement of controls had the greatest effect on reducing the predicted number of infected farms.     

推行养殖场动态监控设施配备可行性分析报告

当前对非洲猪瘟的防控已经进入基本成熟阶段,疫情基本稳定,但疫情隐患仍然存在,各养殖场对非洲猪瘟的防控在意识和措施上出现了松懈,防控设施配置严重滞后,监督部门人员无法进场监督。为了更好地做好对非洲猪瘟防控工作,大力促进生猪生产,保障猪肉市场的供应稳定,保护群众利益,维护社会稳定,巩固脱贫攻坚的成果,经过长时间的调查分析,拟在各养殖场推行安装高清联网动态监控设备,下面具体分析猪场安装监控设备的可行性、必要性,以期对养殖业和动物防疫工作提供一定的参考。     

猪场生物安全系统要点

建立生物安全体系是猪场防控疾病的前提,也是最经济有效的疫病防治措施。2018年我国发生非洲猪瘟以来,疫情对我国生猪养殖业带来深刻影响,在未来很长一段时间内该病都将是我国猪场的常态化疾病。非洲猪瘟疫情发生后,我国养猪业创新性地提出了系列生物安全防控技术,建立了能够有效应对疫情常态威胁的生物安全技术体系,两年多来的防控实践证明了这些生物安全防控手段的有效性。文章总结了猪场生物安全体系建设和管理中的关键环节及注意事项,希望可以为猪场非洲猪瘟防控提供参考。     

Control measures to African swine fever outbreak: active response in South Korea,preparation for the future,and cooperation

African swine fever (ASF) is one of the most complex infectious swine diseases and the greatest concern to the pig industry owing to its high mortality and no effective vaccines available to prevent the disease. Since the first outbreak of ASF in pig farms, ASF has been identified in 14 pig farms in four cities/counties in South Korea. The outbreak was resolved in a short period because of the immediate control measures and cooperative efforts. This paper reviews the ASF outbreak and the experience of successfully stopping ASF in pig farms in South Korea through active responses to prevent the spread of ASF. In addition, suitable changes to build a sustainable pig production system and collaborative efforts to overcome the dangerous animal disease, such as ASF, are discussed.     

The local threshold for geographical spread of infectious diseases between farms

We investigated the influence of the spatial pattern of farms on the geographical spread of infectious livestock diseases, such as classical swine fever, foot-and-mouth disease and avian influenza in a combined analytical-numerical approach. Our purpose of this paper is to develop a method to identify the areas in which an infection has the potential to spread in an outbreak. In our model, each infected farm can infect neighbouring farms and the probability of transmission is a function of the inter-farm distance (spatial kernel). Therefore, the density of farms in an area is a good indicator for the probability of a major outbreak. In the epidemiological nomenclature, such density corresponds to a local reproduction ratio and we studied the critical behaviour of both the local density and the local reproduction ratio. We found that a threshold can be defined above which major outbreaks can occur, and the threshold value depends on the spatial kernel. Our expression for the threshold value is derived based on scaling arguments and contains two parameters in the exponents of the equation. We estimated these parameters from numerical results for the spatial spread using one particular mathematical function for the form of the spatial kernel. Subsequently, we show that our expression for the threshold using these estimated parameters agrees very well with numerical results for a number of different other functional forms of the spatial kernel (thus suggesting that we are dealing with universal parameters). As an illustration of the practical relevance of the presented method, we calculated the threshold value for avian influenza in the Netherlands and use it to produce a risk map for this disease.     

Surveillance of ASF-infected pig farms from September to October 2019 in South Korea

Fourteen African swine fever (ASF) outbreaks occurred in the pig farms in the northwestern region of South Korea, near the border with North Korea, from September 16, 2019 to October 9, 2019. Active and passive surveillance on the ASF-infected farms indicated that the infection was limited only to pigsties where the infected pigs were detected on the farm for the first time before further transmission to other pigsties and farms. This early detection could be one of the pivotal factors for the prompt eradication of ASF in domestic pig farms within 1 month in the northwestern region of South Korea.     

非洲猪瘟背景下猪育种策略探讨

非洲猪瘟给我国养猪业造成巨大损失,也沉重地打击了我国的猪育种工作,虽然目前非洲猪瘟已大大缓解,各核心育种场也逐渐恢复了育种工作,但非洲猪瘟并未消除,未来的育种工作将面临非洲猪瘟常态的挑战。在这样的背景下,我国的猪育种工作应做出针对性的改变,主要体现在：（1）建立严格的永久性的生物安全体系;（2）调整育种目标;（3）自动化、智能化、物联网技术的应用;（4）加快基因组选择技术应用;（5）建设高质量、高度生物安全的种公猪站;（6）利用冷冻精液技术。     

批次化生产在猪场疫病净化中的重要作用

随着中国养猪业规模化、集约化发展步伐的加快,养猪生产正在从劳动密集型的连续生产方式过渡到智能化、批次化养猪的管理新模式,与之相伴而来的是猪新旧疫病的不断发生,其仍然是养猪生产面临的重大挑战,尤其是近两年非洲猪瘟防控形势非常严峻,猪场在疾病防控、生物安全方面遇到了新挑战。批次化生产模式可以使传统连续饲养方式造成的疫病传播得到阻断,在养猪生产中具有重要的实践意义。文章综述了批次化生产的概念、批次化生产在猪场疫病净化中的重要作用。     

A novel spatial and stochastic model to evaluate the within and between farm transmission of classical swine fever virus: II validation of the model

A new, recently published, stochastic and spatial model for the evaluation of classical swine fever virus (CSFV) spread into Spain has been validated by using several methods. Internal validity, sensitivity analysis, validation using historical data, comparison with other models and experiments on data validity were used to evaluate the overall reliability and consistency of the model. More than 100 modifications in input data and parameters were evaluated. Outputs were obtained after 1000 iterations for each new scenario of the model. As a result, the model was shown to be consistent, being the probability of infection by local spread, the time from infectious to clinical signs state, the probability of detection based on clinical signs at day t after detection of the index case outside the control and surveillance zones and the maximum number of farms to be depopulated at day t the parameters that have more influence (>10% of change) on the magnitude and duration of the epidemic. The combination of a within- and between-farm spread model was also shown to give significantly different results than using a purely between-farm spread model. Methods and results presented here were intended to be useful to better understand and apply the model, to identify key parameters for which it will be critical to have good estimates and to provide better support for prevention and control of future CSFV outbreaks.     

Evaluation of the transmission risk of foot-and-mouth disease in Japan

The transmission risk of foot-and-mouth disease (FMD) in Japan was evaluated using a mathematical FMD transmission model. The distance-based transmission rate between farms, which was parameterized using the FMD epidemic data in 2010 in Japan, was used to calculate the local-level reproduction numbers—expected numbers of secondary infections caused by one infected farm—for all cattle and pig farms in the country, which were then visualized as a risk map. The risk map demonstrated the spatial heterogeneity of transmission risk in the country and identified risk areas with higher possibility of disease spread. This result suggests that, particularly in high-risk areas, it is important to prepare for the smooth and efficient implementation of control measures against FMD outbreaks.     

内毒素的生物学特性及其对非洲猪瘟流行下猪只复养的影响

文章就内毒素的生物学特性及其对非洲猪瘟(ASF)流行下的复养猪只健康的影响进行了综述,指出:在当前ASF流行下,认识内毒素(ET)的生物学特性及其对复养猪只健康的影响,近期意义在于猪场的成功复养与成功“拔牙”,以维持猪只的健康生产;远期意义在于开发出有效的细菌ET净化剂,这是一个在人医和兽医学领域所面临的极富挑战性的前沿性研究课题。     

浅谈非洲猪瘟防控措施

非洲猪瘟是一种高度接触性的传染病，对养猪业造成了巨大的损失；随着人们对非洲猪瘟的认识逐步深化，猪场防控措施也逐步在完善；构建完善的生物安全体系是防控的核心，将病毒阻挡在猪场之外；对于有问题的猪场，全面排查和“精准拔牙”，结合抗体检测能够很好地控制住病毒的传播，使猪群稳定下来。     

Assessing biosecurity practices, movements and densities of poultry sites across Belgium, resulting in different farm risk-groups for infectious disease introduction and spread

The existing diversity within poultry systems affects the potential risk of infectious disease introduction and spread. Population data on the level of biosecurity and between-farm contacts is scarce, despite its importance for identifying possible routes of disease transmission. A study was carried out in Belgium to investigate and differentiate professional and hobby poultry sites based on their biosecurity levels and farm movements. Questionnaire data from a total of 37 professional poultry farms, 19 hatcheries and 286 hobby poultry sites were analyzed using a combination of a linear scoring system, a Categorical principal component analysis (CATPCA) and a Two-Step cluster analysis (TSCA). In general, the level of biosecurity was lower in hobby poultry flocks, mainly due to the poor confinement against the outdoor environment and the poor infrastructural hygiene. Most Belgian professional poultry farms and hatcheries had an acceptable level of adoption of standard biosecurity practices, however less attention was given to the way transportation vehicles and employers were brought onto farms and professional visitors welcomed. Considerable variation in the movements and in the structure of the networks arising from these movements was found. Movement frequencies were higher at professional farms compared to hobby farms. Results showed that multiple category farming systems had the highest total movement frequencies. Monthly frequencies of professional visits often exceeded those of poultry and egg movements. Professional and hobby poultry sites were also connected, but movements of poultry and eggs were found only to occur from professional to hobby sites. However, hobby poultry keepers were personally purchasing the poultry and eggs on the professional poultry sites. Six groups of poultry sites were differentiated, which are interpreted as very low to very high risk groups, based on the potential of infectious disease introduction and spread.     

规模猪场密闭连廊及相关设施的设计和应用

自2018年非洲猪瘟传入我国以来,生猪养殖业遭受了沉重打击。建设规模猪场密闭连廊,可有效切断非洲猪瘟等动物疫病的传播途径。广西横县通过设计和应用密闭连廊连接生活区、猪舍、物资熏蒸房、出(进)猪台及死猪出口等端口,使猪舍防疫关口前移,增加了防疫纵深,实现了多层阻断抵御病原传播。本文介绍了密闭连廊及相关设施的设计要点和使用流程,以期为规模猪场落实各项生物安全措施,防控非洲猪瘟等动物疫病提供参考。     

Risk based culling for highly infectious diseases of livestock

ABSTRACT: The control of highly infectious diseases of livestock such as classical swine fever, foot-and-mouth disease, and avian influenza is fraught with ethical, economic, and public health dilemmas. Attempts to control outbreaks of these pathogens rely on massive culling of infected farms, and farms deemed to be at risk of infection. Conventional approaches usually involve the preventive culling of all farms within a certain radius of an infected farm. Here we propose a novel culling strategy that is based on the idea that farms that have the highest expected number of secondary infections should be culled first. We show that, in comparison with conventional approaches (ring culling), our new method of risk based culling can reduce the total number of farms that need to be culled, the number of culled infected farms (and thus the expected number of human infections in case of a zoonosis), and the duration of the epidemic. Our novel risk based culling strategy requires three pieces of information, viz. the location of all farms in the area at risk, the moments when infected farms are detected, and an estimate of the distance-dependent probability of transmission.     

Identification of geographic factors associated with early spread of foot-and-mouth disease

OBJECTIVE: To explore whether early analysis of spatial data may result in identification of variables associated with epidemic spread of foot and mouth disease. SAMPLE POPULATION: 37 farms with infected cattle (ie, case farms) reported within the first 6 days of the 2001 Uruguayan foot-and-mouth disease epidemic. PROCEDURE: A georeferenced database was created and retrospective analysis was performed on case farm location in relation to farm density, cattle density, farm type (ie, beef vs dairy cattle production), road density, case farm distance to the nearest road, farm size, farm ownership, and day of infection. Mean or median results of 1 to 3 day versus 4 to 6 day spatial data were compared. Spatial-temporal associations were investigated by correlation analysis. RESULTS: Comparison of mean or median values between the first 3 days and days 4 to 6 of the epidemic and results of correlation analysis indicated a significant increase in road density, cattle density, and dairy cattle production and a significant decrease in farm size and case farm distance to the nearest road that developed over time. A route that linked most case farms by the shortest possible distance and also considered significantly associated variables was created. It included 86.1% of all case farms reported by 60 days into the epidemic. CONCLUSIONS AND CLINICAL RELEVANCE: Epidemic direction can be assessed on the basis of road density and other spatial variables as early as 6 days into an epidemic. Epidemic control areas may be more effectively identified if local and regional georeferenced data are considered.     

非洲猪瘟形势下猪流行性腹泻的防控措施

自2018年第一例非洲猪瘟疫情报道至今已经两年多了.为了快速扩繁猪群,许多清空场及新建场不得不大量外购来源复杂后备猪进群.因此,猪场在对猪流行性腹泻的防控上面临着更大的挑战.文章介绍了病毒性腹泻暴发的原因、防控难点和综合防控措施,期望为养殖业同人在实际生产中,科学防控猪流行性腹泻提供一定的参考借鉴.     

Basic reproduction number of African swine fever in wild boars (Sus scrofa) and its spatiotemporal heterogeneity in South Korea

BackgroundAfrican swine fever (ASF) is a hemorrhagic fever occurring in wild boars (Sus scrofa) and domestic pigs. The epidemic situation of ASF in South Korean wild boars has increased the risk of ASF in domestic pig farms. Although basic reproduction number (R₀) can be applied for control policies, it is challenging to estimate the R₀ for ASF in wild boars due to surveillance bias, lack of wild boar population data, and the effect of ASF-positive wild boar carcass on disease dynamics.ObjectivesThis study was undertaken to estimate the R₀ of ASF in wild boars in South Korea, and subsequently analyze the spatiotemporal heterogeneity.MethodsWe detected the local transmission clusters using the spatiotemporal clustering algorithm, which was modified to incorporate the effect of ASF-positive wild boar carcass. With the assumption of exponential growth, R₀ was estimated for each cluster. The temporal change of the estimates and its association with the habitat suitability of wild boar were analyzed.ResultsTotally, 22 local transmission clusters were detected, showing seasonal patterns occurring in winter and spring. Mean value of R₀ of each cluster was 1.54. The estimates showed a temporal increasing trend and positive association with habitat suitability of wild boar.ConclusionsThe disease dynamics among wild boars seems to have worsened over time. Thus, in areas with a high elevation and suitable for wild boars, practical methods need to be contrived to ratify the control policies for wild boars.