Editorial

The Global Atlas of Helminth Infection: Mapping the WayForward in Neglected Tropical Disease ControlSimon Brooker1,2*, Peter J. Hotez3,4, Donald A. P. Bundy5

1 London School of Hygiene and Tropical Medicine, London, United Kingdom, 2 Kenya Medical Research Institute-Wellcome Trust Research Programme, Nairobi, Kenya,

3George Washington University, Washington, District of Columbia, United States of America, 4 Sabin Vaccine Institute, Washington, District of Columbia, United States of

America, 5 The World Bank, Washington, District of Columbia, United States of America

The recent commitment of the Obamaadministration to establish the GlobalHealth Initiative, which is expected toincrease to over US$100 million annuallyfor neglected tropical disease (NTD)control, provides the most significantinvestment and opportunity for the globalcontrol of NTDs to date [1,2]. Theseinvestments, together with commitmentsby the British Department for Internation-al Development, the World Bank, andseveral key private philanthropies, includ-ing the Bill & Melinda Gates Foundation,must be guided by a strong evidence-basedapproach. First, the problem, and theresources required to tackle it, need to beclearly quantified. Second, mass drugadministration (MDA) should be optimallytargeted to communities with the highestprevalence of infection and presumedgreatest morbidity [3,4]. Furthermore,for diseases targeted for elimination,including lymphatic filariasis (LF) andonchocerciasis, it will become increasinglyimportant to determine whether MDAcan be stopped, and, if so, when andwhere. In the case of schistosomiasis, ascontrol is scaled up, there is the additionalrequirement of determining when andwhere to shift praziquantel treatment fromonce per year to less frequent intervals.

New Diagnostic Tools

Better diagnostic tools and new methodsof surveillance provide more affordableand realistic opportunities to improve theplanning, monitoring, and evaluation ofNTD control. Diagnosis of onchocerciasiswas previously based on detection ofmicrofilariae in skin snips, but this invasivetechnique is gradually being replaced byantibody-based tests, which can provide asimple and rapid method of diagnosis[5,6]. The development of a simple andrapid antigen detection test for Wuchereriabancrofti antigenaemia, based on the im-muno-chromatographic test (ICT cardtest), revolutionized LF surveys since itavoided the need to collect blood at nightand the time-consuming preparation andexamination of blood slides [7]. Ongoing

efforts are investigating similar rapidantigen detection tests for schistosomiasis[8]. This new generation of diagnosticsprovides a sound foundation for develop-ing reliable, up-to-date maps of thedistribution of different NTDs to guideand target resources efficiently. Withoutsuch maps, the journey of NTD controlwill be difficult.

Mapping of NTDs

In the past, national reporting on NTDshas been incomplete and unreliable be-cause of weak disease surveillance systems,often necessitating dedicated surveys to beundertaken. Perhaps the first attempt todevelop evidence-based maps of any NTDwas that of the African Programme forOnchocerciasis Control (APOC), whichdeveloped the rapid epidemiological map-ping of onchocerciasis (REMO) approachto quickly and cheaply identify priorityareas for community-directed treatmentwith ivermectin (CDTI) and estimate thenumber of individuals requiring treatment[9]. This approach stratifies a country intoareas that are suitable and unsuitable fortransmission, based on known geographicfactors, and within suitable areas imple-ments rapid assessment of communities byscreening individuals for onchocercal nod-ules. In Africa, a total of 23 countries havebeen mapped for onchocerciasis. As coun-

tries have been successful in controllingonchocerciasis, many are now conductingnew REMO assessments to provide up-dated maps. For LF, the rapid geograph-ical assessment of Bancroftian filariasis(RAGFIL) method [10] using ICT cardtests enabled large-scale assessments of theboundaries of filaria-endemic areas foridentifying areas requiring MDA (withalbendazole and ivermectin or diethylcar-bamazine-citrate) [11]. In 2009, all en-demic countries in the World HealthOrganization (WHO)-defined regions ofthe Eastern Mediterranean, South-EastAsia, and Western Pacific have completedmapping, whilst in Africa, 37 of 39endemic countries have completed or arein the process of mapping, with only Chadand Eritrea yet to start [12]. In the case ofschistosomiasis, one of the first steps of theSchistosomiasis Control Initiative (SCI) indesigning country programmes was toconduct national prevalence surveys ofschistosomiasis to identify communitiesand districts requiring mass treatment withpraziquantel [13,14]. Outside SCI-sup-ported countries, national surveys ofschistosomiasis and soil-transmitted hel-minth (STH) infections are often scarceand ad-hoc, with the exception of somededicated surveys, such as those supportedby the Carter Center [15,16] and mostrecently by countries supported by theNTD Initiative of the US Agency for

Citation: Brooker S, Hotez PJ, Bundy DAP (2010) The Global Atlas of Helminth Infection: Mapping the WayForward in Neglected Tropical Disease Control. PLoS Negl Trop Dis 4(7): e779. doi:10.1371/journal.pntd.0000779

Editor: Serap Aksoy, Yale School of Public Health, United States of America

Published July 27, 2010

Copyright: ! 2010 Brooker et al. This is an open-access article distributed under the terms of the CreativeCommons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium,provided the original author and source are credited.

Funding: SB is funded by a research career development from the Wellcome Trust (no. 081673). SB and PJHalso receive funding from the Albert B. Sabin Vaccine Institutes Human Hookworm Vaccine Initiative (HHVI)which is funded by the Bill and Melinda Gates Foundation. This work forms part of the output of the GlobalAtlas of Helminth Infection which is principally funded by the Partnership for Child Development at ImperialCollege UK, Deworm the World, and the Wellcome Trust. The funders had no role in study design, datacollection and analysis, decision to publish, or preparation of the manuscript.

Competing Interests: SB is Deputy Editor and PJH is Editor-in-Chief of PLoS Neglected Tropical Diseases. PJH isan inventor on international patents for hookworm and schistosomiasis vaccines. DAPB is Coordinator of theAPOC program for the World Bank.

* E-mail: simon.brooker@lshtm.ac.uk

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International Development (USAID) [17].Despite these efforts, there remains aconsiderable mapping requirement tosupport global NTD control. Also, it islittle appreciated that as control is success-ful in reducing transmission, there will bean increasing requirement to conductmapping surveys to assess whether to stopMDA or switch to less frequent treatment.

New Mapping Technologies

Future data collection efforts shouldtake advantage of recent advances inrecording and processing data and con-verting data into maps. Increasingly,surveys utilize electronic data capturesystems, mainly based on the use ofpersonal digital assistants (PDAs) but alsosmall laptops, to enter data at the point ofcollection [18] and almost instantaneouslytransmit the information to a centraldatabase using mobile phone technology[19]. Once data have been collected andcollated, geographical information systems(GIS) provide a ready framework in whichto manage and display the data. Thedistribution of NTDs is particularly sensi-tive to climatic and environmental factorsbecause of the vulnerability of vectors,intermediate hosts, and free-living stages.The GIS frameworks allow ready com-parison between disease patterns andenvironmental data, while remote sensing(RS) technologies can use high-resolutionsatellite data to provide estimates of suchvariables as temperature, vegetation (as aproxy for various environmental factors),and humidity [20]. The relationshipsbetween observed infection patterns andenvironmental factors can be investigatedusing both traditional and spatially explicitstatistical approaches [21], allowing thespatial distributions of infection prevalenceto be predicted in unsurveyed areas. Suchanalyses are increasingly adopting aBayesian approach to statistical inferencethat provides a robust method for mea-suring uncertainty in prediction [22,23].Finally, it is perhaps worth emphasizingthat this journal is itself an example of thepower of the new technologies, since theopen-access format permits the data,analyses, and predictions to be publishedin a way that maximizes access to theinformation.

Current Global MappingResources

Although many surveys of differentNTDs have been conducted and manymore are planned, the survey data are onlyuseful if available in a form that is

accessible to policy-makers and the man-agers of public health programmes. Atpresent the most detailed maps availableare for onchocerciasis, LF, and schistoso-miasis. For onchocerciasis, the country-level REMO maps, which highlight theareas where CDTI is needed, are madeavailable through APOCs Web site [24].For schistosomiasis, the most completeglobal resource remains the 1987 Atlas ofthe Global Distribution of Schistosomiasis [25],now available online [26]. For eachcountry, a map is presented that showsthe presence or absence of schistosomiasis.Although these maps represent an impor-tant early source of information, the dataare at best 23 years old and do not includethe wealth of prevalence data collectedmore recently.The preventive chemotherapy (PCT)

databank was developed by WHO as atool to map progress on the implementa-tion of NTD control efforts targeting LF,schistosomiasis, and STH infections [27].The PCT databank includes countryprofiles that present the estimated popula-tion at risk of infection and requiring PCTand, where available, data on treatmentcoverage for each NTD [28]. However,the PCT databank only includes data asreported to WHO and excludes surveyinformation from other sources, such asdata collected by academic researchers,nongovernmental organizations (NGOs),and other partners. The data are present-ed at administrative level 1 (province orregion) and the derived maps inevitablycannot capture the fine-scale heteroge-neity of infection patterns, so they tend tooverestimate the numbers of individualsrequiring treatment.

A Global Atlas of HelminthInfection

In an attempt to provide open access toup-to-date information on schistosomiasisand STH infections, a project has beenundertaken to develop a Global Atlas ofHelminth Infection (GAHI) [29,30]. Theoverall goal of this project is to provide anopen-access, global information resourceon the distribution of STH and schistoso-miasis, with the specific aims of 1)describing the global distribution andprevalence of infection of each speciesand 2) highlighting geographical areas forwhich further survey information is re-quired. The maps are grounded in struc-tured searches of the formal and greyliterature for suitable survey data that arethen collated into a single database,according to specified inclusion criteria.The eligible surveys are geo-positioned

using electronic sources and maps are thendeveloped using GIS. To date, more than10,000 prevalence surveys have beenidentified, catalogued, and mapped. Thepotential usefulness of the data to identifyat risk populations for which data arescarce is enhanced by using Bayesianmodel-based geostatistics [23] to predictthe prevalence of infection with eachspecies in as yet unsurveyed areas.The GAHI Web site will be launched

on August 12, 2010 at http://www.thiswormyworld.org/. The Web site al-lows users to visualize the assembled dataand models. Three types of maps arepresented for every country where theseinfections occur: (i) a Survey Data Mapshowing the prevalence of infection basedon survey data; (ii) a Predictive Risk Mapshowing the probability that infectionprevalence warrants MDA, according torecommended WHO thresholds; and (iii) aControl Planning Map showing which dis-tricts require MDA treatment or wherefurther surveys would be helpful indefining risk.As the URL suggests, inspiration for this

project comes from the work of theAmerican parasitologist Norman Stoll,who, during his 1946 presidential addressto the American Society of Parasitologists,posed the question, just how much humanhelminthiasis is there in the world? Theresultant paper, This Wormy World [31],was the first systematic attempt to measurethe worldwide impact of human parasitismby helminths and provides the foundationfor subsequent attempts to define theburden of NTDs [32]. Building on theGAHI, an ongoing project is developing aGlobal Atlas of Trachoma, expandingearlier attempts to the map the globaldistribution of trachoma [33]. This work isintended to provide an evidence base forallocating resources for trachoma control,including surgery and administration ofZithromax [35].

Conclusion

Accurate and up-to-date maps of differ-ent NTDs can help improve the precisionof decision-making in NTD control. Theycan help increase the reliability of esti-mates of disease burden, for example, aspart of the ongoing revision of the GlobalBurden of Disease study [34]. The mapscan also establish a baseline against whichto measure the impact of NTD controlefforts. Finally, they can provide animportant planning tool for nationalcontrol programmes. Considerable effortis required to develop an integrated NTDatlas, necessitating cooperation and col-

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laboration of the different NTD commu-nities. We hope the Global Atlas of

Helminth Infection will encourage this interaction and help progress towards anopen access Global Atlas of NTDs.

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