Journal articles on the topic 'Epidemic fade-out'

We show that sub-spreading events, i.e. transmission events in which an infection propagates to few or no individuals, can be surprisingly important for defining the lifetime of an infectious disease epidemic and hence its waiting time to elimination or fade-out, measured from the time-point of its last observed case. While limiting super-spreading promotes more effective control when cases are growing, we find that when incidence is waning, curbing sub-spreading is more important for achieving reliable elimination of the epidemic. Controlling super-spreading in this low-transmissibility phase offers diminishing returns over non-selective, population-wide measures. By restricting sub-spreading, we efficiently dampen remaining variations among the reproduction numbers of infectious events, which minimizes the risk of premature and late end-of-epidemic declarations. Because case-ascertainment or reporting rates can be modelled in exactly the same way as control policies, we concurrently show that the under-reporting of sub-spreading events during waning phases will engender overconfident assessments of epidemic elimination. While controlling sub-spreading may not be easily realized, the likely neglecting of these events by surveillance systems could result in unexpectedly risky end-of-epidemic declarations. Super-spreading controls the size of the epidemic peak but sub-spreading mediates the variability of its tail.

The objective of this study was to investigate the dynamics of PRRSV infection and to quantify transmission within a breeding herd, and its impact on herd performance. For this purpose a longitudinal study was performed in a closed breeding herd of 115 sows. Statistical methods and Monte Carlo simulations based on stochastic SIR models were used to analyse the observational data. Moreover, a case-control study was performed to determine whether seroconversion of sows during gestation was associated with aberrant litters. The transmission parameter R was estimated to be 3·0 (95% confidence interval 1·5–6·0) for the model version based on the most plausible assumptions that the infectious period lasts 56 days and no lifelong immunity exists after infection. Based on simulations using a breeding herd of equal size the average time-to-extinction was estimated to be 6 years; using a herd of twice the size, it was 80 years. Furthermore, in contrast to the epidemic phase of the disease, the endemic phase was not detrimental to herd performance.

<span>The COVID-19 epidemic has spread massively to almost all countries including Indonesia, in just a few months. An important step to overcoming the spread of the COVID-19 is understanding its epidemiology through mathematical modeling intervention. Knowledge of epidemic dynamics patterns is an important part of making timely decisions and preparing hospitals for the outbreak peak. In this study, we developed the susceptible-infected-recovered-dead (SIRD) model, which incorporates the key epidemiological parameters to model and estimate the long-term spread of the COVID-19. The proposed model formulation is data-based analysis using public COVID-19 data from March 2, 2020 to May 15, 2021. Based on numerical analysis, the spread of the pandemic will begin to fade out after November 5, 2021. As a consequence of this virus attack, the cumulative number of infected, recovered, and dead people were estimated at ≈ 3,200,000, ≈ 3,437,000 and ≈ 63,000 people, respectively. Besides, the key epidemiological parameter indicates that the average reproduction number value of COVID-19 in Indonesia is 7.32. The long-term prediction of COVID-19 in Indonesia and its epidemiology can be well described using the SIRD model. The model can be applied in specific regions or cities in understanding the epidemic pattern of COVID-19.</span>

<abstract><p>In this work we use simple mathematical models to study the impact of vaccination against COVID-19 in Portugal. First, we fit a SEIR type model without vaccination to the Portuguese data on confirmed cases of COVID-19 by the date of symptom onset, from the beginning of the epidemic until the 23rd January of 2021, to estimate changes in the transmission intensity. Then, by including vaccination in the model we develop different scenarios for the fade-out of the non pharmacological intervention (NPIs) as vaccine coverage increases in the population according to Portuguese vaccination goals. We include a feedback function to mimic the implementation and relaxation of NPIs, according to some disease incidence thresholds defined by the Portuguese health authorities.</p></abstract>

Pertussis has resurfaced in the UK, with incidence levels not seen since the 1980s. While the fundamental causes of this resurgence remain the subject of much conjecture, the study of historical patterns of pathogen diffusion can be illuminating. Here, we examined time series of pertussis incidence in the boroughs of Greater London from 1982 to 2013 to document the spatial epidemiology of this bacterial infection and to identify the potential drivers of its percolation. The incidence of pertussis over this period is characterized by 3 distinct stages: a period exhibiting declining trends with 4-year inter-epidemic cycles from 1982 to 1994, followed by a deep trough until 2006 and the subsequent resurgence. We observed systematic temporal trends in the age distribution of cases and the fade-out profile of pertussis coincident with increasing national vaccine coverage from 1982 to 1990. To quantify the hierarchy of epidemic phases across the boroughs of London, we used the Hilbert transform. We report a consistent pattern of spatial organization from 1982 to the early 1990s, with some boroughs consistently leading epidemic waves and others routinely lagging. To determine the potential drivers of these geographic patterns, a comprehensive parallel database of borough-specific features was compiled, comprising of demographic, movement and socio-economic factors that were used in statistical analyses to predict epidemic phase relationships among boroughs. Specifically, we used a combination of a feed-forward neural network (FFNN), and SHapley Additive exPlanations (SHAP) values to quantify the contribution of each covariate to model predictions. Our analyses identified a number of predictors of a borough’s historical epidemic phase, specifically the age composition of households, the number of agricultural and skilled manual workers, latitude, the population of public transport commuters and high-occupancy households. Univariate regression analysis of the 2012 epidemic identified the ratio of cumulative unvaccinated children to the total population and population of Pakistan-born population to have moderate positive and negative association, respectively, with the timing of epidemic. In addition to providing a comprehensive overview of contemporary pertussis transmission in a large metropolitan population, this study has identified the characteristics that determine the spatial spread of this bacterium across the boroughs of London.

If an infectious agent is to maintain itself within a closed population by means of an unbroken serial chain of infections, it must maintain the level of infectiousness of individuals through time, or termination of the transmission chain is inevitable. One possible cause of diminution in infectiousness along serial chains of transmission may be that individuals are unable to amplify and transmit comparable levels of the infectious agent. Here, the results are reported of a novel experiment designed specifically to assess the effects of serial passage of foot-and-mouth disease virus (FMDV) in experimental groups of sheep. A virus isolate taken from an epidemic of foot-and-mouth disease (FMD) characterized by rapid fade-out of infection was passed serially through four groups of sheep housed in an isolation unit. Although it was not possible to measure individual infectiousness directly, blood virus load from infected individuals was quantified using a real-time PCR assay and used as an underlying indicator of the level of infection. The results of this assay concurred well with those of the traditional tissue-culture assay and were shown to be highly repeatable. The level of peak viraemia was shown to fall significantly with the time of infection and with passage group, both in terms of the group mean and regression analysis of individual values, suggesting that this isolate of FMDV may, under certain conditions, be unable to maintain itself indefinitely in susceptible sheep populations. The results of these experiments are discussed in terms of the epidemiology of FMD in sheep.

SUMMARYScrapie is a fatal transmissible spongiform encephalopathy (TSE) of sheep, endemic in the UK for centuries. Interest in the disease has been heightened over the last decade by the possibility of the related BSE being transmissible to and between sheep and a range of control interventions has been proposed and implemented. In this paper, we examined the effect of these policies and their components on observed case rate, susceptible allele frequency and R0 within the framework of a large simulation model of the British sheep population and its breeding and trading structure. We compared interventions with the natural fade-out of scrapie in the population through loss of susceptible genotypes in the absence of control. We compare the results of interventions with the natural course of the scrapie epidemic. Our model suggested that scrapie will persist in the national flock for 300–400 years with the impact on gene frequencies confined largely to high case-rate breeds, such as Shetland and Swaledale. We found the National Scrapie Plan (NSP) to be the most effective in terms of the removal of both susceptible genotypes and scrapie from the population. Complete eradication of scrapie can be achieved within 32 years (95% CI 23–43 years). The Compulsory Scrapie Flock Scheme (CSFS) is as effective as the NSP in reducing the observed case rate but has a limited impact on the frequencies of susceptible genotypes in the population overall. In combination with the NSP, eradication of scrapie is achieved >10 years faster. Of the components of the CSFS, the breeding and culling aspects are each almost as effective as the full policy, with trading restrictions contributing little. We have speculated on the impact of control measures on the possibility BSE infection within the national flock by examining their effect on flock R0 for BSE across different breeds.

Мы живем в ХХI веке – веке глобализации, высоких скоростей, кризисов, эпидемий и пандемий. Время потребовало кардинальных перемен в политике, экономике, образовании; интегрирования экономических и политических систем разных стран. В связи с этим возникают вопросы мирного сосуществования разных народов и государств, решать которые необходимо ежедневно. Изменяются также роль и значение иностранных языков: те, что ранее представляли огромный интерес для всех окружающих, отходят на второй план, их позиции завоевывают другие. Усиливается интерес к языкам и культуре народов бывшего СССР.В статье рассматриваются вопросы культуры речевого общения в семьях киргизов и, соответственно, некоторые особенности киргизской лексики. Актуальность темы обусловлена увеличением количества иностранных студентов в России, а также взаимовлиянием киргизского и русского языков. Проанализировано влияние русской культуры и русского языка на формирование лексической системы и развитие современной коммуникативной культуры киргизов, которую можно охарактеризовать как культуру коллективистского типа.Киргизский язык исследован недостаточно, научная новизна работы состоит в том, что она включена в ряд исследований, проведенных в РФ и посвященных изучению иностранных языков, и киргизского в частности, что, бесспорно, демонстрирует заинтересованность в изучении особенностей языка и культуры киргизского этноса.Практическая новизна и значимость работы предполагают ее использование при подготовке лекционных занятий по теории межкультурных коммуникаций. Как результат, позволяет повысить эффективность обучения киргизов в вузах РФ. Зная особенности усвоения иностранной лексики киргизами, можно планировать формы и методы работы, а также результаты обучения.Целью работы является описание коммуникативной культуры общения киргизов.Проведен лингвистический эксперимент, методом наблюдения выявлены некоторые особенности коммуникации в киргизских семьях. Отмечены незначительные расхождения в культуре северной и южной Киргизии. Убедились, что культура киргизов носит коллективистский характер вертикального типа. Описаны наиболее эффективные методы изучения русского языка киргизами. Даны практические советы, позволяющие раскрыть способности студентов и ускорить процесс обучения русскому языку.Данная работа продолжает ряд методических работ, главной целью которых является повышение эффективности и качества обучения иностранных студентов русскому языку в технических вузах РФ. We live in the XXI century – the century of globalization, high speeds, crises, epidemics and pandemics. The time required radical changes in politics, economics, education; integration of economic and political systems of different countries. In this regard, questions of peaceful coexistence of different peoples and states arise, which must be resolved on a daily basis. The role and meaning of foreign languages are also changing: those that previously were of great interest to everyone around them fade into the background, their positions are conquered by others. Interest in the languages and culture of the peoples of the former USSR is growing. The article examines the issues of verbal communication culture in Kyrgyz families and, accordingly, some features of the Kyrgyz vocabulary. The relevance of the topic is due to the increase in the number of foreign students in Russia, as well as the mutual influence of the Kyrgyz and Russian languages. The influence of Russian culture and the Russian language on the formation of the lexical system and the development of the modern communicative culture of the Kyrgyz, which can be characterized as a culture of the collectivist type, is analyzed. The Kyrgyz language has not been studied enough, the scientific novelty of the work lies in the fact that it is included in a number of studies conducted in the Russian Federation and devoted to the study of foreign languages and Kyrgyz in particular, which undoubtedly demonstrates an interest in studying the peculiarities of the language and culture of the Kyrgyz ethnos. The practical novelty and significance of the work involves its use in the preparation of lectures on the theory of intercultural communication. As a result, it makes it possible to increase the efficiency of teaching Kyrgyz at universities of the Russian Federation. Knowing the peculiarities of mastering foreign vocabulary by the Kyrgyz, we can plan forms and methods of work, as well as learning outcomes. The aim of the work is to describe the communicative culture of communication of the Kyrgyz. A linguistic experiment has been carried out, some features of communication in Kyrgyz families have been revealed by the observation method. Minor differences were noted in the culture of northern and southern Kyrgyzstan. We were convinced that the culture of the Kyrgyz is of a collectivist nature of a vertical type. The most effective methods of studying the Russian language by the Kirghiz are described. Practical advice is given to reveal the abilities of students and to speed up the process of teaching the Russian language. This work continues a series of methodological works, the main goal of which is to increase the efficiency and quality of teaching the Russian language to foreign students in technical universities of the Russian Federation.

We present a detailed analysis of the pattern of measles outbreaks in the small isolated community of the Faroe Islands. Measles outbreaks in this population are characterized by frequent fade-out of infection resulting in long intervals when the disease is absent from the islands. Using an analysis of the distribution of epidemic sizes and epidemic durations we propose that the dynamical structure observed in the measles case returns reflects the existence of an underlying scaling mechanism. Consequently the dynamics are not as purely stochastic as is usually thought for epidemiological systems of this sort. We use a lattice-based epidemic model to provide a theoretical estimate of the scaling exponents and show that a conventional compartmental SEIR model is unable to reproduce this result. The methods discussed in this paper are general and represent a novel way to consider the dynamics of any other communicable disease where there is frequent fade-out in the case returns.

ABSTRACT Avian-origin H3N2 canine influenza virus (CIV) transferred to dogs in Asia around 2005, becoming enzootic throughout China and South Korea before reaching the United States in early 2015. To understand the posttransfer evolution and epidemiology of this virus, particularly the cause of recent and ongoing increases in incidence in the United States, we performed an integrated analysis of whole-genome sequence data from 64 newly sequenced viruses and comprehensive surveillance data. This revealed that the circulation of H3N2 CIV within the United States is typified by recurrent epidemic burst–fade-out dynamics driven by multiple introductions of virus from Asia. Although all major viral lineages displayed similar rates of genomic sequence evolution, H3N2 CIV consistently exhibited proportionally more nonsynonymous substitutions per site than those in avian reservoir viruses, which is indicative of a large-scale change in selection pressures. Despite these genotypic differences, we found no evidence of adaptive evolution or increased viral transmission, with epidemiological models indicating a basic reproductive number, R0, of between 1 and 1.5 across nearly all U.S. outbreaks, consistent with maintained but heterogeneous circulation. We propose that CIV's mode of viral circulation may have resulted in evolutionary cul-de-sacs, in which there is little opportunity for the selection of the more transmissible H3N2 CIV phenotypes necessary to enable circulation through a general dog population characterized by widespread contact heterogeneity. CIV must therefore rely on metapopulations of high host density (such as animal shelters and kennels) within the greater dog population and reintroduction from other populations or face complete epidemic extinction. IMPORTANCE The relatively recent appearance of influenza A virus (IAV) epidemics in dogs expands our understanding of IAV host range and ecology, providing useful and relevant models for understanding critical factors involved in viral emergence. Here we integrate viral whole-genome sequence analysis and comprehensive surveillance data to examine the evolution of the emerging avian-origin H3N2 canine influenza virus (CIV), particularly the factors driving ongoing circulation and recent increases in incidence of the virus within the United States. Our results provide a detailed understanding of how H3N2 CIV achieves sustained circulation within the United States despite widespread host contact heterogeneity and recurrent epidemic fade-out. Moreover, our findings suggest that the types and intensities of selection pressures an emerging virus experiences are highly dependent on host population structure and ecology and may inhibit an emerging virus from acquiring sustained epidemic or pandemic circulation.

The Zika virus has emerged as a global public health concern. Its rapid geographic expansion is attributed to the success of Aedes mosquito vectors, but local epidemiological drivers are still poorly understood. Feira de Santana played a pivotal role in the Chikungunya epidemic in Brazil and was one of the first urban centres to report Zika infections. Using a climate-driven transmission model and notified Zika case data, we show that a low observation rate and high vectorial capacity translated into a significant attack rate during the 2015 outbreak, with a subsequent decline in 2016 and fade-out in 2017 due to herd-immunity. We find a potential Zika-related, low risk for microcephaly per pregnancy, but with significant public health impact given high attack rates. The balance between the loss of herd-immunity and viral re-importation will dictate future transmission potential of Zika in this urban setting.