Health Metrics for Helminths Infections

Center for Global Health and Diseases, Case Western Reserve University School of Medicine, Cleveland, OH, USA.
Advances in Parasitology (Impact Factor: 6.23). 12/2010; 73:51-69. DOI: 10.1016/S0065-308X(10)73003-7
Source: PubMed


Over the past five decades, accurate and comparable assessment of disease burden due to different 'worm' infections has proven problematic. Estimates of the health impact of helminths have varied significantly, depending on the assessor's perspective and the approaches taken to quantifying disease effects on patient performance status. Past surveys have frequently suffered from misclassification bias due to the lack of a diagnostic 'gold' standard. At the same time, there has been a tendency to define disease based solely on late-onset, 'pathognomonic' outcomes that can be uniquely attributed to each pathogen. However, we are now gaining a much better understanding of the role of helminths in anaemia causation, impaired growth and development, and poor school or work performance. With a new appreciation of the link between long-term, parasite-mediated inflammation and the patient's lifetime risk of disability, we recognise that the bulk of worm-associated diseases is found in the latter, 'non-specific' categories, with relevance to individual performance status and detriment to regional levels of human capital. Appropriately, the emerging use of comprehensive disability metrics such as the quality-adjusted life year (QALY)-as opposed to the widely used disability-adjusted life year (DALY) metrics-will better capture the impact of helminthic infections on the long-term health of Asian and other developing world populations. This improved, more valid assessment is expected to provide evidence favouring preventive over curative intervention for control of these highly prevalent diseases.

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Available from: Charles H King
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    • "More generally, the use of DALYs as a measure of disease burden has its advantages and its disadvantages [95]. The main advantage is that DALYs provide a composite, internally consistent measure of population health which can be used to evaluate the relative burden of different diseases and injuries and compare population health by geographic region and over time. "
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    ABSTRACT: Quantifying the burden of parasitic diseases in relation to other diseases and injuries requires reliable estimates of prevalence for each disease and an analytic framework within which to estimate attributable morbidity and mortality. Here we use data included in the Global Atlas of Helminth Infection to derive new global estimates of numbers infected with intestinal nematodes (soil-transmitted helminths, STH: Ascaris lumbricoides, Trichuris trichiura and the hookworms) and use disability-adjusted life years (DALYs) to estimate disease burden. Prevalence data for 6,091 locations in 118 countries were sourced and used to estimate age-stratified mean prevalence for sub-national administrative units via a combination of model-based geostatistics (for sub-Saharan Africa) and empirical approaches (for all other regions). Geographical variation in infection prevalence within these units was approximated using modelled logit-normal distributions, and numbers of individuals with infection intensities above given thresholds estimated for each species using negative binomial distributions and age-specific worm/egg burden thresholds. Finally, age-stratified prevalence estimates for each level of infection intensity were incorporated into the Global Burden of Disease Study 2010 analytic framework to estimate the global burden of morbidity and mortality associated with each STH infection. Globally, an estimated 438.9 million people (95% Credible Interval (CI), 406.3 - 480.2 million) were infected with hookworm in 2010, 819.0 million (95% CI, 771.7 - 891.6 million) with A. lumbricoides and 464.6 million (95% CI, 429.6 - 508.0 million) with T. trichiura. Of the 4.98 million years lived with disability (YLDs) attributable to STH, 65% were attributable to hookworm, 22% to A. lumbricoides and the remaining 13% to T. trichiura. The vast majority of STH infections (67%) and YLDs (68%) occurred in Asia. When considering YLDs relative to total populations at risk however, the burden distribution varied more considerably within major global regions than between them. Improvements in the cartography of helminth infection, combined with mathematical modelling approaches, have resulted in the most comprehensive contemporary estimates for the public health burden of STH. These numbers form an important benchmark upon which to evaluate future scale-up of major control efforts.
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    • "One explanation for the slow awakening to the role of NTDs is that their mortality is generally low and they often present with only subtle symptoms that hamper assessment of their burden. For example, hookworm infection and schistosomiasis are leading causes of anaemia [5,6] that can result in delayed cognitive development, poor school/work performance and impaired growth [7-9]. In addition, lack of sufficiently sensitive diagnostic tools undermine reliable assessments of prevalence and intensity of disease [10,11], and this weakness becomes acute in areas where disease control has progressed significantly since the combination of low levels of infection and low prevalence produces a negative bias. "
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    ABSTRACT: Poverty magnifies limitations posed by traditional biases and environmental risks. Any approach towards disease control needs to recognise that socially embedded vulnerabilities can be as powerful as externally imposed infections. Asia Pacific has a specific panorama of infectious diseases, which, in common with other endemic areas, have a tendency to emerge or re-emerge if not carefully monitored. Sustained control aiming at elimination requires strong emphasis on surveillance and response. Well-designed informatics platforms can improve support systems and strengthen control activities, as they rapidly locate high-risk areas and provide detailed, up-to-date information on the performance of ongoing control programmes.
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    • "Quantifying the level of protozoan parasite infection using commonly applied metrics such as the DALY (e.g. Pruss et al., 2002) is impractical unless gross non-specific estimates are required as distinguishing between all possible sources of infection and the confounding impact of polyparasitism is rarely if ever possible (Payne et al., 2009; King, 2010). Epidemiological analysis of focal point contaminations such as water or specific food contamination events can provide good estimates of the spread and impact of parasite infection, but on a global scale, due to the uncertainty caused by the scarcity of data (Payne et al., 2009) the impact of these occurrences remains poorly understood. "
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    ABSTRACT: A growing number of enteric protozoan species are considered to have zoonotic potential. Their clinical impact varies and in many cases is poorly defined. Similarly, the epidemiology of infections, particularly the role of non-human hosts, requires further study. In this review, new information on the life cycles and transmission of Giardia, Cryptosporidium, Entamoeba, Blastocystis and Balantidium are examined in the context of zoonotic potential, as well as polyparasitism and clinical significance.
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