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| Author | : Celia Holland |
| Publisher | : Newnes |
| Total Pages | : 461 |
| Release | : 2013-05-09 |
| Genre | : Medical |
| ISBN | : 012397285X |
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This book tackles a number of different perspectives concerning the parasitic helminth Ascaris, both in animals and in humans and the disease known as ascariasis. It seeks to identify interesting, exciting and novel aspects, which will interest readers from a broad range of disciplines.Over a quarter of the world's population are infected with the human roundworm, and the equivalent in pigs is equally ubiquitous. Both contribute to insidious and chronic nutritional morbidity, and this has been quantified, in humans, as disability adjusted life years approximating 10.5 million. Ascaris larvae develop in host parenteral tissues, and the resultant pathology has been condemnation. Ascariasis, despite its staggering global prevalence and the sheer numbers of people it infects, remains a classic neglected disease. However, renewed interest in the consequences of early infection with worms from the perspective of immune modulation, co-infections and the development of allergy further enhances the relevance of these parasites. Brings together a wide range of topics and approaches and recent, comprehensive and progressive research concerning the neglected parasite Ascaris Provides a blueprint of how a single parasite entity can stimulate interest in basic biology, clinical science, veterinary science, public health and epidemiology Presents a wealth of new insights given that a book on this parasite has not been published for over 20 years 16 chapters from a range of top authors from around the world
| Author | : Simon J. Brooker |
| Publisher | : Elsevier Inc. Chapters |
| Total Pages | : 33 |
| Release | : 2013-05-09 |
| Genre | : Medical |
| ISBN | : 0128061367 |
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Ascariasis is a neglected tropical disease (NTD) affecting 763 million people worldwide, with nutritional and developmental consequences of chronic childhood infection and severe clinical disease occurring in heavy infections. Reliably estimating the extent of the problem of Ascaris lumbricoides and ascariasis is difficult because of inaccuracies in parasitological diagnosis, the non-specificity of clinical signs, and a paucity of reliable and accurate data. As a consequence, estimating the global distribution and disease burden has been based on informed approximations, using the best available information. This chapter provides an overview of past and current estimates of the global population at risk of and infected with A. lumbricoides. The regional and global burden of ascariasis is estimated by extrapolation from data on the prevalence of infection and a series of epidemiological methods. The Global Burden of Disease (GBD) study uses disability-adjusted life years (DALYs) to measure disease burden, based on an assessment of premature mortality and years lived with disability. The data and methods used to estimate the disease burden of ascariasis in the 1990 GBD study and the 2010 study are compared. Globally, intestinal nematodes are estimated to contribute 5.184 million DALYs in 2010, with ascariasis contributing 1.3148 million, trichuriasis 0.6382 million, and hookworm 3.2311 million. The 2010 study provides estimates for both 1990 and 2010, and these findings indicated that the burden of ascariasis in 2010 is much lower than in 1990, where ascariasis contributed 4.2173 billion DALYs. The use of DALYs to estimate the burden of ascariasis is not without its limitations, however, and fails to capture the broader societal impact of ascariasis and other NTDs or that they disapportionally affect the poorest populations.
| Author | : Martin Walker |
| Publisher | : Elsevier Inc. Chapters |
| Total Pages | : 68 |
| Release | : 2013-05-09 |
| Genre | : Medical |
| ISBN | : 0128061308 |
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In the context of the current unprecedented momentum and commitment to control neglected tropical diseases, and the increased advocacy of anthelmintic mass drug administration (MDA), there are renewed calls for research and development into the epidemiology and population biology of helmintic parasites to be embedded at the core of intervention strategies. This review of the epidemiology of Ascaris lumbricoides – one of the three neglected soil-transmitted helminth infections of greatest public health importance – includes discussion on diagnostic methods and their limitations; patterns of transmission within communities, including heterogeneities in infection and reinfection following curative treatment; the geographical distribution of infection, and the role of environmental, climatic and socio-economic co-variables. Special emphasis is placed on the mathematical approaches that underpin contemporary parasite epidemiology. In particular, statistical models – for analyzing highly variable, overdispersed, zero-inflated and hierarchically or spatially structured data – and dynamic models of infection and transmission. Deterministic, stochastic and hybrid dynamic models are discussed in the context of their application in elucidating the interplay between the parasite frequency distribution and density-dependent population processes; the dynamics of reinfection following curative treatment; the sustainability of parasite populations at low densities; theoretical threshold densities (transmission breakpoints) for elimination; and the potential spread of anthelmintic resistance. The review highlights the public health relevance of mathematical models and analytical methods, and concludes by focusing on recent insights into the epidemiology of A. lumbricoides which are particularly germane to the effective implementation of MDA-based control.
| Author | : Charles D. Criscione |
| Publisher | : Elsevier Inc. Chapters |
| Total Pages | : 38 |
| Release | : 2013-05-09 |
| Genre | : Medical |
| ISBN | : 0128061316 |
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The fields of conservation genetics and genetic epidemiology share many parallel questions. Hence, methodologies can be adapted from the former to the latter. Three applications of population genetics are presented to further our understanding of Ascaris epidemiology. (1) I address if Ascaris infections in humans and pigs constitute a single population or subdivided host-affiliated populations with potential for cross-transmission and hybridization. (2) I discuss the use of landscape genetics as a means to identify transmission foci and epidemiologically relevant variables correlated to parasite population substructure. (3) I propose the novel integration of the effective population size (Ne) parameter into population monitoring and epidemiological studies of parasites in general. Using microsatellite data from a metapopulation of A. lumbricoides in Nepal, I demonstrate the utility of estimating Ne with single-sample contemporary estimators, offer epidemiologically related questions that can be addressed with Ne, and highlight assumptions of Ne estimation related to Ascaris biology.
| Author | : Celia V. Holland |
| Publisher | : Elsevier Inc. Chapters |
| Total Pages | : 30 |
| Release | : 2013-05-09 |
| Genre | : Medical |
| ISBN | : 0128061286 |
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Larval ascariasis is much less well understood than adult worm infection. Part of the explanation for this is the difficulty in assessing the impact of larval infections in human subjects. In contrast, adult worms can be counted after post-chemotherapeutic expulsion or, additionally, eggs voided in host feces can be quantified as an indirect measure of infection intensity. Furthermore, respiratory and hepatic disease, which may be associated with transient passage of larvae through these organs, can be either non-specific or cryptic, making Ascaris-specific diagnosis through clinical signs of infection challenging. The influence of early infection on parasite establishment and host immunity is recognized as important but it remains challenging to unravel the complexities of the relationship. Both pigs as natural hosts of Ascaris suum and a range of abnormal hosts have been utilized to investigate larval migration. Few if any of these model systems have enabled clarification of the basis of variation in susceptibility and resistance to larval migration and accumulation in the liver and lungs. In this chapter, we document the literature on larval ascariasis with a particular emphasis on studies utilizing mice because mice are now developing as useful model systems for the study of early Ascaris infection, the migratory path and its duration being similar to that of pigs. We describe a mouse model of early Ascaris infection that mimics the extremes of the host phenotype displayed in the aggregated distribution of adult worms in human and pig populations, outline the existing evidence for the role of the liver in susceptibility to larval ascariasis and discuss future directions for the use of this model system.
| Author | : T. Déirdre Hollingsworth |
| Publisher | : Elsevier Inc. Chapters |
| Total Pages | : 52 |
| Release | : 2013-05-09 |
| Genre | : Medical |
| ISBN | : 0128061324 |
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Mathematical models are playing an increasing role in the design and optimization of control programs for many infectious diseases. In the case of Ascaris lumbricoides, there is a long history of models to understand the biology and epidemiology and to design control programs. We outline the key insights which models have given on the dynamics of Ascaris transmission, describe the model structures and discuss how current and future models are informing the design of control programs in the era of both increased access to donate drugs and new statistical techniques to validate these models against reinfection data. We show how the “bounce-back” time following a treatment round, when infection levels monotonically increase to baseline levels, are driven by the life expectancy of the parasite and the basic reproductive number. We also show that the effect of treatment in subsets of the population, for example school children, depends on the extent to which different subpopulations interact with the egg output of the treated group. We discuss the outstanding policy questions which models can be used to answer and the data and model development required to address them.
| Author | : Johnny Vlaminck |
| Publisher | : Elsevier Inc. Chapters |
| Total Pages | : 41 |
| Release | : 2013-05-09 |
| Genre | : Medical |
| ISBN | : 0128061391 |
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Roundworms are the most prevalent parasite of swine in the world today. Their presence on a pig farm can have detrimental effects on farm profitability due to their impact on growth rate, feed conversion, and general health of the produced pigs. For farmers, it is therefore essential to be aware of the “worm status” of their herd in order to make informed decisions on how to control this disease on their farm. This chapter concentrates on the diverse aspects involved in the diagnosis and control of Ascaris suum infections on pig farms. It focuses on how the results obtained from different detection methods should be interpreted and what efforts could be made to control parasite transmission and consequentially reduce the prevalence and economic impact of this parasite on a pig farm.
| Author | : Malcolm W. Kennedy |
| Publisher | : Elsevier Inc. Chapters |
| Total Pages | : 45 |
| Release | : 2013-05-09 |
| Genre | : Medical |
| ISBN | : 012806126X |
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In comparison with other helminths that afflict humans on a global scale, Ascaris lumbricoides and ascariasis are relatively under-researched in terms of the proteins and other products to which the parasites expose their hosts. The reputation of the parasite as a source of potent allergens, and the recognition that immune hypersensitivity in the lung caused by migrating larvae is a significant problem, has served to focus attention on immune responses to Ascaris. Research has increasingly focused on the parasite’s products and responses to them in experimental rodents, and in pigs as permissive hosts for the full life-cycle of Ascaris suum. In parallel, immunoepidemiology of ascariasis in humans has been developing, often aimed at understanding how the infection polarizes immune responses. This review deals with the antigens of the parasite, how the immune repertoire to them varies dramatically between infected humans, the genetic loci that are probably involved, and its unpredictability. New work on the molecular structure of the unusual proteins produced by Ascaris and other nematodes is also covered, including the well-known ABA-1 allergen. Emphasis is also placed on a poorly understood aspect of Ascaris immunobiology, prompted by a few tantalizing observations, namely the potential diversity of surface and secreted antigens of the human parasite, and how such polymorphisms could be crucial to understanding the chronicity of ascariasis in the face of continuous loss and recruitment of the parasites themselves.
| Author | : Martha Betson |
| Publisher | : Elsevier Inc. Chapters |
| Total Pages | : 32 |
| Release | : 2013-05-09 |
| Genre | : Medical |
| ISBN | : 0128061332 |
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To better understand the epidemiology of ascariasis, molecular genetic methods have been applied to differentiate between worms found infecting people and pigs, and other occasional hosts. Owing to difficulties in applying species concepts, the longstanding debate of the distinction(s) between Ascaris lumbricoides and Ascaris suum continues. From an applied perspective, however, molecular markers help to “tag” and “track” worms during their transmission cycle(s), providing new insights into host range, as well as methods for assessing parasite population dynamics through time and contingent upon disease control. While useful in determining dynamics at the tips of the evolutionary tree, these molecular tools also provide insights into deeper evolutionary branches. Although Ascaris is found throughout the globe, molecular analysis of worms retrieved from sub-Saharan Africa point towards a significant center of genetic diversity, possibly denoting a likely center of evolutionary origin with subsequent parasite diaspora. Resolving these issues precisely, however, requires greater scrutiny of genetic variation within Parascaris and Baylisascaris.
| Author | : Antony O.W. Stretton |
| Publisher | : Elsevier Inc. Chapters |
| Total Pages | : 38 |
| Release | : 2013-05-09 |
| Genre | : Medical |
| ISBN | : 0128061294 |
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The structural simplicity of nematode nervous systems has provided a useful resource for studies on basic neurobiology. Two species have underpinned basic neuroscience research in phylum Nematoda, the free-living nematode Caenorhabditis elegans and the pig parasitic nematode Ascaris suum due to their genetic tractability and large size, respectively. The fact that most of the chemotherapeutic targets for the treatment of roundworm parasite infections of animals and man associate with neuromuscular function means that nematode neurobiology research resonates beyond discovery biology and informs parasite control. These diverse drivers for the interrogation of nematode neurobiology have exposed a unique approach to the regulation of complex behavioral traits, encompassing structural simplicity with profound chemical complexity. The latter embraces extreme diversity in both the ligand-gated ion channel subunit complements for classical neurotransmitters and in the neuropeptide ligands that signal mostly via G-protein coupled receptors, offering compelling opportunities for parasite control-target discovery and validation.
