The ABC of terms used in mathematical models of infectious diseases

Mathematical models that incorporate a dynamic risk of infection figure prominently in the study of infectious diseases epidemiology as a tool to inform public health policy. In recent years, their use has expanded to address methodological questions, inform and validate study design and evaluate interventions. This glossary briefly highlights the applications of transmission dynamics modelling, explains different modelling methodologies and defines commonly encountered terms to provide an introductory and conceptual understanding of the vocabulary and frameworks used in the literature.     

建立数学模型用于口岸传染病控制实践

传染病是由病原微生物入侵人体所引起的一类疾病,能通过入出境旅客输入输出国境口岸并引起局部或广泛的流行。     

The use of simple epidemiological models in the evaluation of disease control programmes: a case study of trachoma

One of the problems in the quantitative evaluation of disease control programmes is the definition of a “critical” index reflecting the effect of control measures on the various aspects of a polymorphic disease. Trachoma is an example of a polymorphic disease in which its activity, intensity, severity, etc., are affected by control measures, including their timing. A simple epidemiological model indicated that the “force of infection” is a sufficient parameter to describe changes in the disease picture following a control programme. Use was made of two trachoma prevalence sample surveys in the same communities, one carried out in 1960-61 and the other in 1968-69. Total trachoma age-prevalence histograms were constructed and simple catalytic curves fitted with the help of a computer programme developed for this purpose. A reduction in the force of infection in the cohort born after the institution of control measures was found. Its projection to the whole community indicated that the control programme had reduced the disease load to 20.1%, i.e., about two-fifths of its former level.     

The epidemiological impact of antiretroviral use predicted by mathematical models: a review

This review summarises theoretical studies attempting to assess the population impact of antiretroviral therapy (ART) use on mortality and HIV incidence. We describe the key parameters that determine the impact of therapy, and argue that mathematical models of disease transmission are the natural framework within which to explore the interaction between antiviral use and the dynamics of an HIV epidemic. Our review focuses on the potential effects of ART in resource-poor settings. We discuss choice of model type and structure, the potential for risk behaviour change following widespread introduction of ART, the importance of the stage of HIV infection at which treatment is initiated, and the potential for spread of drug resistance. These issues are illustrated with results from models of HIV transmission. We demonstrate that HIV transmission models predicting the impact of ART use should incorporate a realistic progression through stages of HIV infection in order to capture the effect of the timing of treatment initiation on disease spread. The realism of existing models falls short of properly reproducing patterns of diagnosis timing, incorporating heterogeneity in sexual behaviour, and describing the evolution and transmission of drug resistance. The uncertainty surrounding certain effects of ART, such as changes in sexual behaviour and transmission of ART-resistant HIV strains, demands exploration of best and worst case scenarios in modelling, but this must be complemented by surveillance and behavioural surveys to quantify such effects in settings where ART is implemented.     

A mathematical model for the epidemiologic study of infectious diseases

Many infectious diseases have been hypothesized to represent common virus infections in which only small proportions of cases result in clinically recognizable disease. In order to find a method of studying this class of diseases, a mathematical model of the age distribution of clinical disease was developed using poliomyelitis as a prototype. The model is shown to fit the age distribution of reported poliomyelitis in a variety of localities before the use of artificial immunization. The true yearly rate of infection is easily estimated and ranges from .11 in rural Sweden to 1.20 in Chile. The model accounts for several major features of poliomyelitis epidemiology, including the shift to older ages and the high rate of clinically apparent disease which were frequently observed in populations which could be expected to have a comparatively low rate of spread. An examination of the age distribution of other diseases by these methods may provide a method of identifying other common infections which only occasionally result in clinically apparent disease.     

系统发育研究在传染病分子流行病学中的应用

测序技术的快速发展导致病原体基因数据急剧增加,将这些数据与系统发育分析方法相结合,可用于阐述病原体的起源和进化、流行过程中的时空分布、参数变化以及抗原、毒力、耐药性等表型特征变化规律、病原体传播趋势预测等。本文简述了系统发育研究的目的和系统发育树的构建方法,阐述了距离法、最大简约法、最大似然法、贝叶斯法等常用系统发育重...     

The design and implementation of effective epidemiological surveillance programmes in Sub-Saharan Africa

Livestock is one of the main sources of wealth in developing countries. The improvement of national herds and of their productivity through controlling the main diseases and preventing epizootics is a major objective in these countries. The organisation of surveillance systems is indispensable to proper animal health management, both nationally and internationally. Therefore, thanks to foreign assistance, developing countries have gradually established epidemiological surveillance networks, despite unfavourable contexts (poverty, lack of resources or infrastructure...). To date, many networks are operating in satisfactory manner and produce tangible results. However, further efforts must be made to improve the quality of sanitary information produced, its performance and sustainability. This article discusses the context and motivations for the establishment of epidemiological surveillance networks in developing countries, especially in Africa, by describing some of their operational specificities and some results. Finally, it presents the example of a Mauritanian animal disease epidemiological surveillance network and its role in managing a health crisis.     

The concept of herd immunity and the design of community-based immunization programmes.

The paper focuses on the concepts of transmission success and herd immunity and their relevance to the design of community-based immunization programmes for the control of infectious diseases. Recent work in a number of areas is reviewed, including the influence of mass vaccination on the average age of infection and the incidence of morbidity due to infection and vaccination, the age window of susceptibility and the problems of vaccine programme design in developing countries, the interaction between vaccine efficacy and vaccine safety and the design of vaccination programmes for the control of sexually transmitted infections. Discussions centre on the interplay between an understanding of the transmission dynamics of an infection and the design of community-based control programmes.     

Economic evaluation of programmes aiming at eradicating infectious diseases

The subject of this article is to discuss the global and regional economic aspects of programmes for eradicating infectious diseases. The perspective on the issue is that scarce health care resources should be employed in the best possible way. The task is then to examine what the best possible use might be. A starting point is by asking the relevant policy questions attached to eradications: Is there a suitable technique, what are the costs, and what are the benefits? Of particular importance is the opportunity cost of using resources on eradication when other health care problems may require more urgent donation of resources. The paper attempts to set up a generic model for economic evaluation of eradication programmes. But, as there are many different treatment strategies varying from one country to another, such a generic model may need modifications to suit a particular strategy. However, the paper is contextual and should only be viewed as guidance for those wishing to conduct an economic analysis of eradication programmes, or as a initiative to create discussion among health care decision makers.     

我国主要蜱媒传染病的流行特征及研究进展

蜱媒传染病（TBDs）已成为世界性的公共卫生问题。近年来,随着我国TBDs自然疫源地的扩大与变迁,发病人数呈上升趋势,并且存在病原复合感染的现实威胁和新发病原感染的潜在威胁,对人类的健康造成了严重的危害。此文围绕我国TBDs的流行特征及研究进展进行综述。     

Epidemiological models of poliomyelitis and measles and their application in the planning of immunization programmes

This report describes the construction and application of epidemiological models of measles and poliomyelitis. In these models, epidemiological classes and their age structure have been based on the natural history of these diseases in the population aged 0 - 19 years. The flow of the population through the classes has been expressed as an equation system suitable for computer interpretation. The models have been used to simulate both the natural course of the diseases and the effect of various immunization schemes. The models were also used to explore prospects for control and eradication of these diseases with specific immunization programmes, and their relative effectiveness and cost-effectiveness are discussed.     

The transmission dynamics of hepatitis B in the UK: a mathematical model for evaluating costs and effectiveness of immunization programmes.

Complex hepatitis B (HBV) epidemiology makes it difficult to evaluate and compare effectiveness of different immunization policies. A method for doing so is presented using a mathematical model of HBV transmission dynamics which can represent universal infant and adolescent vaccination strategies and those targeted at genito-urinary (GU) clinic attenders and infants born to infectious mothers. Model structure, epidemiological underpinning, and parameterization, are described. Data from the UK National Survey of Sexual Attitudes and Lifestyles is used to define patterns of sexual activity and GU clinic attendance; data deficiencies are discussed, in particular that of UK seroprevalence of HBV markers stratified by age, sex, and risk factors. General model predictions of endemic HBV marker prevalence in homosexual and heterosexual populations seem consistent with published UK data. The simulations exhibit non-linearities in the impact of different vaccination strategies. Estimated number of carriers prevented per vaccine dose for each strategy provides a measure of costs and benefits, varying temporally over the course of a programme, and with level of vaccine coverage. Screening before vaccination markedly increases payback per dose in homosexuals but not in heterosexuals; mass infant vaccination gives the poorest effectiveness ratio and vaccination of infants after antenatal screening the best; in general, increasing vaccine coverage yields lower pay-back per dose. The model provides a useful framework for evaluating costs and benefits of immunization programmes, but for precise quantitative comparison more UK epidemiological data is urgently needed.     

Immunogenicity of oral poliovirus vaccine administered in mass campaigns versus routine immunization programmes.

Reported are the results of a study to investigate the immunogenicity of oral poliovirus vaccine (OPV) when administered in mass campaigns compared with that following routine immunization programmes. For this purpose, paired sera were collected from a cohort of children before and after a mass vaccination with OPV in Morocco in 1987. Serum samples and information on vaccination status and other confounding factors that could influence antibody responses to OPV were collected. Neutralizing antibody titres to poliovirus types 1, 2 and 3 were determined using a standardized assay. OPV doses administered exclusively during the mass campaign were consistently associated with higher type-specific seroprevalence rates than the same number of doses administered in the routine programme. These findings could not be attributed to differences in confounding factors. Enhanced secondary spread of vaccine virus may have occurred but could not be demonstrated because of limitations in the study design. Mass campaigns appear to be highly effective in raising the dose-related poliovirus type-specific immunity of the population above that achieved by the routine immunization programme. Our findings support the continued use of mass campaigns as an adjunct to routine programmes in order to both enhance and catalyse current efforts to achieve the global eradication of poliomyelitis by the year 2000.