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Parasitic and infectious diseases: Epidemiology and ecology
Book reviews
68
average 14 households) which can be given a map grid reference accurate to 100 m and thereby approximated into census enumeration districts, and thus into published population data. There is a useful review of how one can estimate population for years when census counts are not available. The problems and methods of estimating and mapping environmental exposure are well and thoroughly reviewed, though relatively brief. There are five valuable chapters reviewing statistical methods, especially for those whose eyes cross when presented with formulae with more than two independent variables and those squiggly things with dangling alphabet. They discuss the problems of mean exposure assessment when there is a wide heterogeneity in exposure and the dangers of assuming that the individual dose-response relationship is linear. Then of selecting appropriate latency periods; one needs 15-20 years between smoking data and mortality but shorter latencies can be used for well defined groups, such as birth data and childhood leukaemia for Chernobyl accidents. With longer latencies one is caught in the circular problem of increasing migration diluting apparent impacts, especially in small communities. Geographic studies are best at hypothesis generation and identifying major risks, not at estimating their strengths and interactions. These can be best studied in detailed investigations. This is also true of clustering. Statistical tests can determine whether it is present. Whether they are real is something else. These chapters are then followed by three on aspects of actually investigating clusters of adverse health events. These have mud on their boots and are rich with experience. The steps cover not only procedural design but also communication with the communities and the media, organizational requirements, legal ramifications, politics, and the investigator’s responsibility to neither encourage unwarranted public concern nor false reassurance. For those trained in shoe-leather epidemiology, they are a breath of fresh air and a vision of reality when hunched over a computer terminal tweaking mathematical models. The text finishes with six chapters covering specific case studies which reiterate and illustrate points made earlier throughout the book. The case study on excess childhood leukaemias near nuclear powerplants is valuable because they are not consistant. Richard Doll has recently suggested a feline leukaemia model explanation, based on excess children and infants in the construction community. This book can be confidently recommended for graduate students, career and research epidemiologists, and especially those in public health. MARTIN HUGH-JONES Department
of Epidemiology & Community Health School of Veterinary Medicine Louisiana State University Baton Rouge
LA 70803 SSDIO167-5877(94)00460-9
USA
Parasitic and infectious diseases: epidemiology and ecology and Ecology. Marilyn E Scott and Gary Smith (Editors), Academic Press, 1994,398 pp., US$95.00, ISBN O-12633325-4.
Parasitic and Infectious Diseases: Epidemiology
Book reoiews
69
This book is principally a compendium of mathematical analyses of host, parasite and vector dynamical systems. It is the intention of the editors that the material should be suitable for students of the medical, veterinary, and biological sciences. The book is such that each chapter is a separate paper written by different authors. A total of 27 authors contribute to the 24 chapters. The papers can be classified into three types - educational introduction, modelling processes, and case studies. The initial chapters focus on providing the reader with an educational introduction to the terminology and some of the mathematical methods to come later. This is exceptionally good in view of the targeted readership. All too often papers published in journals are restricted by length and the uninformed, but interested, reader is not sufficiently prepared for the harsh brevity with which modelers deliver their mathematical equations. Many of these shortcomings are addressed in these early chapters. The “So you want to write a model” chapter is really good and raises the expectation that somehow the reader will be gently led through the modeler’s warehouse. Similarly, the following chapters give introductory expositions on stability, the basic reproduction index, and density regulation. The chapter on experimental and theoretical approaches to quantifying population processes is one of the few that touches on the broader issue of how to estimate parameters .and raises some awareness of the problems of random variation. Unfortunately, a further opportunity to increase awareness of the breadth of epidemiology is missed when the explanation of standard measures of disease occurrence fails to make the link to field conditions as is done in classical texts on veterinary epidemiology. The educational theme disappears too quickly as the chapters move towards a second theme with separate papers on the role of modelling processes in genetics, nutrition, vaccination, chemotherapy, and vector control. Many of the chapters on processes are purely descriptive and void of any quantitative relationships, which seems at odds with the opening chapters. Nevertheless, these chapters bring home the paradox of the complexity of parasitic systems and the need to reduce information to key components if methods of disease eradication or control are to be identified. Such chapters inevitably end up with a tribute to the benefits of modelling while the subject matter is not always totally convincing. The one exception is the discussion on the impact of vaccination. This chapter is inspirational and firmly demonstrates how theory can include the complexities of age structure, maternal antibodies, and vaccination regimens. It also weds theory to the practicalities of the control of smallpox, measles, and rubella. What is interesting is that no chapter was commissioned on the effect of physical environmental factors which, from the remarks in later chapters, can have a considerable influence on whether or not a parasitic species exists in a given spatial location as well as influencing seasonal levels of challenge. The final eleven chapters are mostly organized according to disease, and population models are discussed for associated parasites, vectors, and disease outbreaks. The mathematical content of these case reports varies, with some expositions being entirely descriptive and others focusing firmly on the mathematical complexities. Human diseases include ascariasis, schistosomiasis, measles, echinococcosis, and Lyme disease. Both the discussion of the demography of tick populations and of chaos in the context of measles are noteworthy. On the veterinary side models are presented for nematodes of the ruminants and grouse. A historical account of the spread of myxomatosis in Australia is presented along with some
70
Book reviews
recent epidemiological data on virulence. A final chapter offers interesting possibilities for modelling larval nematodes of seals. It should be noted that the modelling and epidemiological perspectives adopted throughout the book are very focused. They essentially promulgate one particular school of modelling where the emphasis is firmly placed on the use of differential equations to describe population behavior. This inevitably leads to discussions of equilibrium behavior and reproductive indices. Thus a reader moving from chapter to chapter is likely to find the methodology repetitive. Moreover, most of these modelling methods are deterministic and do little to address issues of variability. No attempt is made to enlighten the reader as to how extensive the rich array of modelling methods really is. In particular, statistical models such as log linear models, which are widely used in epidemiology to assess risk, do not even appear in the subject index. The editors have intentionally chosen the particular focus but this is not apparent from the book title or preface. This book is not like any other book. It is a curious mixture of teaching material and specialist-domain reviews of particular methods and diseases. It has tried to span both medical and veterinary diseases. So who should buy this book? In view of the dearth of good modelling texts this book is a must for the modelling community. Not only is it a quality production with a serious attempt at promoting the practice of modelling but all too often such specialist books fail to reprint in sufficient numbers. It will also be of interest to other groups. Veterinary students of parasitic diseases with an interest in biological modelling will find it a useful reference book and a source of inspiration but they are likely to access it as a library book in view of the price. Veterinary researchers with an interest in one of the specific diseases will be keen to see what the modelers and epidemiologists can bring to the table. Professional decision makers are likely to find the approaches interesting, but there may be insufficient attention given to the impact of models to convince them that it holds the master key. Readers of Preoentioe Veterinary Medicine should feel comfortable with the broad aims of the material but many will need help if they are to devise working protocols to test and refine those models which may improve animal production and welfare. In summary, this is one of the few books on parasitic diseases that brings together applications of a particular school of modelling to a wide range of diseases. It makes a significant contribution to the literature.
SSDIOl67-5877(94)00461-7
GEORGE GETTINBY Department of Statistics & Model&g Science Strathclyde Unioersity Glasgow UK
68
average 14 households) which can be given a map grid reference accurate to 100 m and thereby approximated into census enumeration districts, and thus into published population data. There is a useful review of how one can estimate population for years when census counts are not available. The problems and methods of estimating and mapping environmental exposure are well and thoroughly reviewed, though relatively brief. There are five valuable chapters reviewing statistical methods, especially for those whose eyes cross when presented with formulae with more than two independent variables and those squiggly things with dangling alphabet. They discuss the problems of mean exposure assessment when there is a wide heterogeneity in exposure and the dangers of assuming that the individual dose-response relationship is linear. Then of selecting appropriate latency periods; one needs 15-20 years between smoking data and mortality but shorter latencies can be used for well defined groups, such as birth data and childhood leukaemia for Chernobyl accidents. With longer latencies one is caught in the circular problem of increasing migration diluting apparent impacts, especially in small communities. Geographic studies are best at hypothesis generation and identifying major risks, not at estimating their strengths and interactions. These can be best studied in detailed investigations. This is also true of clustering. Statistical tests can determine whether it is present. Whether they are real is something else. These chapters are then followed by three on aspects of actually investigating clusters of adverse health events. These have mud on their boots and are rich with experience. The steps cover not only procedural design but also communication with the communities and the media, organizational requirements, legal ramifications, politics, and the investigator’s responsibility to neither encourage unwarranted public concern nor false reassurance. For those trained in shoe-leather epidemiology, they are a breath of fresh air and a vision of reality when hunched over a computer terminal tweaking mathematical models. The text finishes with six chapters covering specific case studies which reiterate and illustrate points made earlier throughout the book. The case study on excess childhood leukaemias near nuclear powerplants is valuable because they are not consistant. Richard Doll has recently suggested a feline leukaemia model explanation, based on excess children and infants in the construction community. This book can be confidently recommended for graduate students, career and research epidemiologists, and especially those in public health. MARTIN HUGH-JONES Department
of Epidemiology & Community Health School of Veterinary Medicine Louisiana State University Baton Rouge
LA 70803 SSDIO167-5877(94)00460-9
USA
Parasitic and infectious diseases: epidemiology and ecology and Ecology. Marilyn E Scott and Gary Smith (Editors), Academic Press, 1994,398 pp., US$95.00, ISBN O-12633325-4.
Parasitic and Infectious Diseases: Epidemiology
Book reoiews
69
This book is principally a compendium of mathematical analyses of host, parasite and vector dynamical systems. It is the intention of the editors that the material should be suitable for students of the medical, veterinary, and biological sciences. The book is such that each chapter is a separate paper written by different authors. A total of 27 authors contribute to the 24 chapters. The papers can be classified into three types - educational introduction, modelling processes, and case studies. The initial chapters focus on providing the reader with an educational introduction to the terminology and some of the mathematical methods to come later. This is exceptionally good in view of the targeted readership. All too often papers published in journals are restricted by length and the uninformed, but interested, reader is not sufficiently prepared for the harsh brevity with which modelers deliver their mathematical equations. Many of these shortcomings are addressed in these early chapters. The “So you want to write a model” chapter is really good and raises the expectation that somehow the reader will be gently led through the modeler’s warehouse. Similarly, the following chapters give introductory expositions on stability, the basic reproduction index, and density regulation. The chapter on experimental and theoretical approaches to quantifying population processes is one of the few that touches on the broader issue of how to estimate parameters .and raises some awareness of the problems of random variation. Unfortunately, a further opportunity to increase awareness of the breadth of epidemiology is missed when the explanation of standard measures of disease occurrence fails to make the link to field conditions as is done in classical texts on veterinary epidemiology. The educational theme disappears too quickly as the chapters move towards a second theme with separate papers on the role of modelling processes in genetics, nutrition, vaccination, chemotherapy, and vector control. Many of the chapters on processes are purely descriptive and void of any quantitative relationships, which seems at odds with the opening chapters. Nevertheless, these chapters bring home the paradox of the complexity of parasitic systems and the need to reduce information to key components if methods of disease eradication or control are to be identified. Such chapters inevitably end up with a tribute to the benefits of modelling while the subject matter is not always totally convincing. The one exception is the discussion on the impact of vaccination. This chapter is inspirational and firmly demonstrates how theory can include the complexities of age structure, maternal antibodies, and vaccination regimens. It also weds theory to the practicalities of the control of smallpox, measles, and rubella. What is interesting is that no chapter was commissioned on the effect of physical environmental factors which, from the remarks in later chapters, can have a considerable influence on whether or not a parasitic species exists in a given spatial location as well as influencing seasonal levels of challenge. The final eleven chapters are mostly organized according to disease, and population models are discussed for associated parasites, vectors, and disease outbreaks. The mathematical content of these case reports varies, with some expositions being entirely descriptive and others focusing firmly on the mathematical complexities. Human diseases include ascariasis, schistosomiasis, measles, echinococcosis, and Lyme disease. Both the discussion of the demography of tick populations and of chaos in the context of measles are noteworthy. On the veterinary side models are presented for nematodes of the ruminants and grouse. A historical account of the spread of myxomatosis in Australia is presented along with some
70
Book reviews
recent epidemiological data on virulence. A final chapter offers interesting possibilities for modelling larval nematodes of seals. It should be noted that the modelling and epidemiological perspectives adopted throughout the book are very focused. They essentially promulgate one particular school of modelling where the emphasis is firmly placed on the use of differential equations to describe population behavior. This inevitably leads to discussions of equilibrium behavior and reproductive indices. Thus a reader moving from chapter to chapter is likely to find the methodology repetitive. Moreover, most of these modelling methods are deterministic and do little to address issues of variability. No attempt is made to enlighten the reader as to how extensive the rich array of modelling methods really is. In particular, statistical models such as log linear models, which are widely used in epidemiology to assess risk, do not even appear in the subject index. The editors have intentionally chosen the particular focus but this is not apparent from the book title or preface. This book is not like any other book. It is a curious mixture of teaching material and specialist-domain reviews of particular methods and diseases. It has tried to span both medical and veterinary diseases. So who should buy this book? In view of the dearth of good modelling texts this book is a must for the modelling community. Not only is it a quality production with a serious attempt at promoting the practice of modelling but all too often such specialist books fail to reprint in sufficient numbers. It will also be of interest to other groups. Veterinary students of parasitic diseases with an interest in biological modelling will find it a useful reference book and a source of inspiration but they are likely to access it as a library book in view of the price. Veterinary researchers with an interest in one of the specific diseases will be keen to see what the modelers and epidemiologists can bring to the table. Professional decision makers are likely to find the approaches interesting, but there may be insufficient attention given to the impact of models to convince them that it holds the master key. Readers of Preoentioe Veterinary Medicine should feel comfortable with the broad aims of the material but many will need help if they are to devise working protocols to test and refine those models which may improve animal production and welfare. In summary, this is one of the few books on parasitic diseases that brings together applications of a particular school of modelling to a wide range of diseases. It makes a significant contribution to the literature.
SSDIOl67-5877(94)00461-7
GEORGE GETTINBY Department of Statistics & Model&g Science Strathclyde Unioersity Glasgow UK