Global numbers of infection and disease burden of soil transmitted helminth infections in 2010

Abstract

BackgroundQuantifying 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.MethodsPrevalence 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.ResultsGlobally, 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.ConclusionImprovements 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.

The Dynamics of Ascaris lumbricoides Infections

“…It has been present in human populations for thousands of years (Cox 2002). It was originally widely prevalent throughout the world (Tyson 1683, Stoll 1947, Crompton 2001, but was largely eradicated from developed countries in the 20th century (the Japanese experience is described by WHO (1996)), and developed countries (North America, Europe, Russia) now only register a handful of cases (Pullan et al 2014, Crompton 2001. Recent estimates put the number of people infected at 820 million, with considerably more at risk (Pullan et al 2014).…”

Immunity to gastrointestinal nematode infections

“…1 As with many other pathogens, parasitic worm infections are prevalent among children in developing countries where hygienic conditions are poor, with symptoms ranging from abdominal pain and mild anemia to diarrhea, stunted growth, and impaired cognitive development; a tragedy given that most nematodes are easily avoided by improvements in basic hygiene, such as access to clean drinking water. Efforts to treat infected individuals with antihelminthic drugs are thus rendered relatively ineffective in the long term because of continued exposure to infective eggs and larvae in the immediate environment, frequently resulting in reinfection.…”

Water Resource, Hygienic Practice, and Soil Transmitted Helminthiasis in Some Rural Communities of Osun State, Nigeria

“…Soil-Transmitted Helminths (STH) infections affect more than 2 billion people worldwide, with the greatest indices in sub-Saharan Africa, Americas, China and East-Asia [1] [2] [3] [4]. Four species of worms cause most infection: Ascaris lumbricoides, Trichuris trichiura, Ancylostoma duodenale and Necator americanus [5].…”