Transmission dynamics and control of severe acute respiratory syndrome

Severe acute respiratory syndrome (SARS) is a recently described illness of humans that has spread widely over the past 6 months. With the use of detailed epidemiologic data from Singapore and epidemic curves from other settings, we estimated the reproductive number for SARS in the absence of interventions and in the presence of control efforts. We estimate that a single infectious case of SARS will infect about three secondary cases in a population that has not yet instituted control measures. Public-health efforts to reduce transmission are expected to have a substantial impact on reducing the size of the epidemic.     

Explaining seasonal fluctuations of measles in Niger using nighttime lights imagery

Measles epidemics in West Africa cause a significant proportion of vaccine-preventable childhood mortality. Epidemics are strongly seasonal, but the drivers of these fluctuations are poorly understood, which limits the predictability of outbreaks and the dynamic response to immunization. We show that measles seasonality can be explained by spatiotemporal changes in population density, which we measure by quantifying anthropogenic light from satellite imagery. We find that measles transmission and population density are highly correlated for three cities in Niger. With dynamic epidemic models, we demonstrate that measures of population density are essential for predicting epidemic progression at the city level and improving intervention strategies. In addition to epidemiological applications, the ability to measure fine-scale changes in population density has implications for public health, crisis management, and economic development.     

The foot-and-mouth epidemic in Great Britain: pattern of spread and impact of interventions

We present an analysis of the current foot-and-mouth disease epidemic in Great Britain over the first 2 months of the spread of the virus. The net transmission potential of the pathogen and the increasing impact of control measures are estimated over the course of the epidemic to date. These results are used to parameterize a mathematical model of disease transmission that captures the differing spatial contact patterns between farms before and after the imposition of movement restrictions. The model is used to make predictions of future incidence and to simulate the impact of additional control strategies. Hastening the slaughter of animals with suspected infection is predicted to slow the epidemic, but more drastic action, such as "ring" culling or vaccination around infection foci, is necessary for more rapid control. Culling is predicted to be more effective than vaccination.     

Unifying the epidemiological and evolutionary dynamics of pathogens

A key priority for infectious disease research is to clarify how pathogen genetic variation, modulated by host immunity, transmission bottlenecks, and epidemic dynamics, determines the wide variety of pathogen phylogenies observed at scales that range from individual host to population. We call the melding of immunodynamics, epidemiology, and evolutionary biology required to achieve this synthesis pathogen "phylodynamics." We introduce a phylodynamic framework for the dissection of dynamic forces that determine the diversity of epidemiological and phylogenetic patterns observed in RNA viruses of vertebrates. A central pillar of this model is the Evolutionary Infectivity Profile, which captures the relationship between immune selection and pathogen transmission.     

New strategies for the elimination of polio from India

The feasibility of global polio eradication is being questioned as a result of continued transmission in a few localities that act as sources for outbreaks elsewhere. Perhaps the greatest challenge is in India, where transmission has persisted in Uttar Pradesh and Bihar despite high coverage with multiple doses of vaccine. We estimate key parameters governing the seasonal epidemics in these areas and show that high population density and poor sanitation cause persistence by not only facilitating transmission of poliovirus but also severely compromising the efficacy of the trivalent vaccine. We analyze strategies to counteract this and show that switching to monovalent vaccine may finally interrupt virus transmission.     

Molecular evolution of the SARS coronavirus during the course of the SARS epidemic in China

Sixty-one SARS coronavirus genomic sequences derived from the early, middle, and late phases of the severe acute respiratory syndrome (SARS) epidemic were analyzed together with two viral sequences from palm civets. Genotypes characteristic of each phase were discovered, and the earliest genotypes were similar to the animal SARS-like coronaviruses. Major deletions were observed in the Orf8 region of the genome, both at the start and the end of the epidemic. The neutral mutation rate of the viral genome was constant but the amino acid substitution rate of the coding sequences slowed during the course of the epidemic. The spike protein showed the strongest initial responses to positive selection pressures, followed by subsequent purifying selection and eventual stabilization.     

Magmatically triggered slow slip at Kilauea Volcano, Hawaii

We demonstrate that a recent dike intrusion probably triggered a slow fault-slip event (SSE) on Kilauea volcano's mobile south flank. Our analysis combined models of Advanced Land Observing Satellite interferometric dike-intrusion displacement maps with continuous Global Positioning System (GPS) displacement vectors to show that deformation nearly identical to four previous SSEs at Kilauea occurred at far-field sites shortly after the intrusion. We model stress changes because of both secular deformation and the intrusion and find that both would increase the Coulomb failure stress on possible SSE slip surfaces by roughly the same amount. These results, in concert with the observation that none of the previous SSEs at Kilauea was directly preceded by intrusions but rather occurred during times of normal background deformation, suggest that both extrinsic (intrusion-triggering) and intrinsic (secular fault creep) fault processes can lead to SSEs.     

2003年北京市SARS疫情空间相关性分析

空间数据相关性分析是针对具有空间属性的事物之间的相互关系进行有效的认知和解释,以便于辅助预测与调控的方法手段.SARS疾病的突然爆发与蔓延,为区域的发展带来极大的损失,有效认识SARS疫情的空间过程,对于其防治的决策具有重要意义.本文利用北京市公布的SARS病例数据,采用空间数据相关性分析手段,试图分析出SARS的空间过程.结果发现,整个SARS的空间聚集状态存在两个转折点,即人群对疾病的恐慌并迁移引起的疫情扩散和对疫情采取有效防治策略、定点医院的成立后疾病的空间聚集,及后期疾病得到有效控制,呈现零星发作状态而出现空间扩散趋势.新增病例的热点探测证实了空间聚集度的变化趋势,而以街道社区尺度进行的密切接触者的热点探测分析则表明:SARS的空间传播,最早应该是一级热点区域(主要分布在二环内)随机分布状态,后随着人群的空间分布与流动,而出现与人群分布相关的热点区域分布状态.     

Obesity and the environment: where do we go from here?

The obesity epidemic shows no signs of abating. There is an urgent need to push back against the environmental forces that are producing gradual weight gain in the population. Using data from national surveys, we estimate that affecting energy balance by 100 kilocalories per day (by a combination of reductions in energy intake and increases in physical activity) could prevent weight gain in most of the population. This can be achieved by small changes in behavior, such as 15 minutes per day of walking or eating a few less bites at each meal. Having a specific behavioral target for the prevention of weight gain may be key to arresting the obesity epidemic.     

数字技术助力疫情防控智能化——以社区为中心的病毒快速检测追踪平台方案

[目的/意义]新冠病毒全球大流行给全球各国造成了严重损失,在疫情暴发初期忽视大规模的病毒快速检测以及并未采取防控措施切断病毒传播,是导致疫情快速蔓延的重要原因。如何实现病毒快速检测,提升病毒检测效率,并精准定位感染者展开救治、降低感染范围成为疫情防控的关键。[方法/过程]本文以新冠病毒快速检测追踪为切入点,提出构建病毒快速检测追踪平台的方案设想。综合考虑社区封闭式管理以及基层医疗卫生机构在疫情防控中发挥的关键作用,为降低人员流动,减少人群感染风险,本文将生物传感器、人工智能、区块链、大数据技术相融合,充分发挥生物传感器的检测能力、人工智能的学习能力、区块链的信息传递能力、大数据的分析能力,设计以社区为中心的病毒快速检测追踪平台方案。[结果/结论]通过对方案的分析,以社区为中心的病毒快速检测追踪平台具有快速检测,智能诊断,信息共享、安全、可溯源,以及全维度分析的优势,随着新兴技术的不断成熟,期望本研究能为全球疫情防控智能化提供创新方案。     

Profile. Preventing infections with today's tools

With no vaccine in sight powerful enough to halt the spread of HIV, Africa is left with one strategy to combat the epidemic: prevention. The University of Manitoba's Frank Plummer, who oversees a large research collaboration in Nairobi, Kenya, says his group has identified a half-dozen effective interventions to lower HIV transmission rates, but "the scale at which they're implemented is tiny."     

An experimental study of search in global social networks

We report on a global social-search experiment in which more than 60,000 e-mail users attempted to reach one of 18 target persons in 13 countries by forwarding messages to acquaintances. We find that successful social search is conducted primarily through intermediate to weak strength ties, does not require highly connected "hubs" to succeed, and, in contrast to unsuccessful social search, disproportionately relies on professional relationships. By accounting for the attrition of message chains, we estimate that social searches can reach their targets in a median of five to seven steps, depending on the separation of source and target, although small variations in chain lengths and participation rates generate large differences in target reachability. We conclude that although global social networks are, in principle, searchable, actual success depends sensitively on individual incentives.     

具有年龄结构的SI传染病模型的分析

研究了具有年龄结构的单种群模型在成年种群间染病的问题,建立并分析了具有成年和幼年两个年龄结构的SI传染病模型,利用微分方程定性分析方法讨论了该模型平衡点的存在条件,根据平衡点的系数矩阵对应的特征方程的特征根的情况,判断出各个平衡点的类型及局部稳定性,同时利用Hurwitz判别法得到模型的唯一正平衡点局部渐近稳定的充分条件。该结论说明在一定的条件下,疾病对生物种群不会造成较大的影响,不会造成种群的灭绝。     

Large shifts in pathogen virulence relate to host population structure

Theory on the evolution of virulence generally predicts selection for an optimal level of virulence determined by trade-offs with transmission and/or recovery. Here we consider the evolution of pathogen virulence in hosts who acquire long-lived immunity and live in a spatially structured population. We show theoretically that large shifts in virulence may occur in pathogen populations as a result of a bistability in evolutionary dynamics caused by the local contact or social population structure of the host. This model provides an explanation for the rapid emergence of the highly virulent strains of rabbit hemorrhagic disease virus.     

Chelex-100快速提取动物源饲料DNA方法的建立

为防止疯牛病疫区反刍动物源性饲料传入我国,非常有必要对贸易往来中的肉骨粉品种来源进行鉴定。本文建立了一种利用Chelex—100快速提取动物源性饲料DNA的方法,用于反刍动物源性饲料的PCR扩增分析。结果显示该方法与GuSCN法、SDS法同样理想,从而实现了对进境饲料的快速检定的要求。该方法检测灵敏度达到牛成分含量为0．1％的水平,具有简单、快捷、灵敏度高的优点。     

灰飞虱传水稻病毒病控害减灾技术的研究

近10多年来,水稻条纹叶枯病、黑条矮缩病相继在江苏盐城流行,为此,我们较全面、系统、深入调查研究了水稻条纹叶枯病、黑条矮缩病的灾变规律和防控技术。摸清了灰飞虱发生、传毒和病毒病的流行致灾规律,明确了一些水稻品种的抗耐病性,以及防虫网阻隔、适当迟播、耕翻灭茬等农业、物理措施在控制灰飞虱发生和传毒的作用,筛选出一批化学农药品种,为有效防治灰飞虱、预防病毒病提供了高效、低毒的对路药剂。集成一套适合本地现行种植方式,易于操作,可持续的灰飞虱传水稻病毒控害减灾技术,供各地借鉴参考。     

染病食饵种群中疾病的持久性和灭绝性

研究在食饵种群中疾病传播的传染病模型,得到了捕食者是如何控制在食饵种群中的疾病的流行,给出了疾病持久和灭绝的条件,并且分析了捕食者对食饵优先选择的影响.     

小麦条锈菌致病性及其变异研究进展

小麦条锈病（wheat stripe rust or yellow rust）是一种气传性的低温真菌病害,在所有小麦产区均可暴发流行,造成巨大的产量和经济损失,严重威胁着小麦的安全生产。其病原条形柄锈菌小麦专化型（Puccinia striiformis West. f. sp. tritici Eriks. & Henn.,Pst）为严格专性寄生真菌,致病性变异频繁,常造成小麦品种抗条锈性“丧失”,引发病害大流行。因而,从20世纪50年代起,条锈菌致病性变异的研究一直备受关注,并已开展了大量的研究工作。本文从小麦品种抗病性丧失、条锈菌致病性变异途径、条锈菌群体遗传、条锈菌基因组和功能基因组以及条锈菌效应蛋白等不同方面概述了近年来取得的重要研究进展,提出了未来条锈病防治上面临的问题和挑战;以期通过准确预测条锈菌优势小种、合理利用和布局抗病基因、利用新策略创制新型持久广谱抗病材料,不断优化和完善小麦条锈病综合治理技术体系,实现小麦条锈病可持续控制。     

几种常用杀虫药剂对烟粉虱种群数量的影响

研究了黄瓜大田内几种常用杀虫剂对烟粉虱种群数量的控制作用,结果表明：阿维菌素、吡虫啉和扑虱灵均是防治烟粉虱较好的杀虫剂,其中以吡虫啉效果最佳,其干扰作用控制指数为0．0472,表明吡虫啉施用区烟粉虱的种群数量只相当于对照区的4．72％,其次为阿维菌素和扑虱灵,其干扰作用控制指数分别为0．1019和0．1551．由于烟粉虱对乐果等有机磷杀虫剂具有较强的抗性以及乐果对天敌的杀伤,乐果施用区内烟粉虱出现大量发生和猖獗危害现象,干扰作用控制指数达到1．0762,即烟粉虱种群数量为对照区的1．0762倍,因此应该停止使用这类杀虫剂来防治烟粉虱．     

植物病毒分子群体遗传学研究进展

植物病毒群体遗传学的2个中心任务是定量描述病毒种群内的遗传变异及阐明该变异的机制.植物病毒自然种群遗传结构通常包括1-2种优势的序列变异类型和一些低频率的序列变异类型,即具有准种遗传结构特征.植物病毒种群遗传多样性水平和病害暴发以及流行时间有一定的相关性.另外,植物病毒种群遗传结构中还存在超群种群类型.一些生物学特性可能取决于准种内的不同变种间的相互作用.如决定适应能力、寄主范围及致病性变异等.植物寄主—昆虫介体—病毒三者间的协同进化关系是植物病毒种群遗传结构保存相对稳定的主要因素.描述植物病毒种群遗传结构特征为构建更有效的病害防治策略提供了依据.