Am. J. Trop. Med. Hyg., 73(3), 2005, pp. 523–533 Copyright © 2005 by The American Society of Tropical Medicine and Hygiene EFFECT OF WATER RESOURCE DEVELOPMENT AND MANAGEMENT ON LYMPHATIC FILARIASIS, AND ESTIMATES OF POPULATIONS AT RISK TOBIAS E. ERLANGER, JENNIFER KEISER, MARCIA CALDAS DE CASTRO, ROBERT BOS, BURTON H. SINGER, MARCEL TANNER, AND JÜRG UTZINGER* Swiss Tropical Institute, Basel, Switzerland; Department of Geography, University of South Carolina, Columbia, South Carolina; Water, Sanitation and Health, World Health Organization, Geneva, Switzerland; Office of Population Research, Princeton University, Princeton, New Jersey Abstract. Lymphatic filariasis (LF) is a debilitating disease overwhelmingly caused by Wuchereria bancrofti, which is transmitted by various mosquito species. Here, we present a systematic literature review with the following objectives: (i) to establish global and regional estimates of populations at risk of LF with particular consideration of water resource development projects, and (ii) to assess the effects of water resource development and management on the frequency and transmission dynamics of the disease. We estimate that globally, 2 billion people are at risk of LF. Among them, there are 394.5 million urban dwellers without access to improved sanitation and 213 million rural dwellers living in close proximity to irrigation. Environmental changes due to water resource development and management consistently led to a shift in vector species composition and generally to a strong proliferation of vector populations. For example, in World Health Organization (WHO) subregions 1 and 2, mosquito densities of the Anopheles gambiae complex and Anopheles funestus were up to 25-fold higher in irrigated areas when compared with irrigation-free sites. Although the infection prevalence of LF often increased after the implementation of a water project, there was no clear association with clinical symptoms. Concluding, there is a need to assess and quantify changes of LF transmission parameters and clinical manifestations over the entire course of water resource developments. Where resources allow, integrated vector man- agement should complement mass drug administration, and broad-based monitoring and surveillance of the disease should become an integral part of large-scale waste management and sanitation programs, whose basic rationale lies in a systemic approach to city, district, and regional level health services and disease prevention. INTRODUCTION scale operations were launched in 2000, alongside the forging of a worldwide coalition, the Global Alliance to Eliminate People living in tropical and subtropical countries have Lymphatic Filariasis (GAELF), which is a free and nonre- long suffered under the yoke of lymphatic filariasis (LF). This strictive partnership forum. WHO serves as its secretariat and chronic parasitic disease is of great public health and socio- is being reinforced by an expert technical advisory group.12–14 economic significance and is currently endemic in 80 coun- GPELF’s goal is to eliminate the disease as a public health tries/territories of the world.1–3 LF accounts for serious dis- problem by 2020. It mainly relies on mass drug administration figuration and incapacitation of the extremities and the geni- using albendazole plus either ivermectin or diethylcarba- tals and causes hidden internal damage to lymphatic and renal mazine (DEC). At the end of 2003, approximately 70 million systems.4–6 Disease, disability, and disfiguration are respon- people were treated and 36 countries had an active control sible for a loss of worker productivity, significant treatment program in place.14 costs, and social stigma.7,8 At present, the global burden of LF Sustained political and financial commitment and rigorous is estimated at 5.78 million disability adjusted life years monitoring and surveillance are essential elements of the (DALYs) lost annually.9 Hence, its estimated burden is al- global program, as otherwise LF could reemerge because a most 3.5-fold higher than that of schistosomiasis and approxi- small fraction of the population will continue to carry microfi- mately one seventh of that of malaria.9 LF is caused by laria. Furthermore, the vector population is unlikely to be Wuchereria bancrofti, Brugia malayi, and Brugia timori, with significantly affected by GPELF. Employing a mathematical > 90% of cases attributable to W. bancrofti.1 Transmission modeling approach, it was shown that vector control pro- occurs through various mosquito species, primarily Culex grams, in addition to mass drug administration, would sub- (57%), followed by Anopheles (39%), Aedes, Mansonia, and stantially increase the chances of meeting GPELF’s ambitious Ochlerotatus. Detailed information on the geographical dis- target.15 Indeed, some of the most successful control pro- tribution of the most important LF vectors can be found else- grams in the past demonstrate that an integrated approach, where.2 More than 60% of all LF infections are concentrated readily adapted to specific eco-epidemiologic settings, was a in Asia and the Pacific region, where Culex is the predomi- key factor for controlling and even eliminating LF.16–19 nant vector. In Africa, where an estimated 37% of all infec- In rural areas undergoing ecological transformations, par- tions occur, Anopheles is the key vector.2 ticularly due to the construction of irrigation schemes and In 1993, the World Health Organization (WHO) declared dams, new breeding sites suitable for filaria vectors are cre- LF to be one of six eliminable infectious diseases.10 After ated.16,20 As a consequence, the transmission dynamics of LF several years of preparation and endorsement by the World is expected to change. In Africa, where Anopheles transmit Health Assembly in 1997, the Global Program to Eliminate malaria and filaria, the estimated surface area of 12 million ha Lymphatic Filariasis (GPELF) was initiated in 1998.11 Large- under irrigation in 1990 is estimated to increase by one third until 2020.21 Rapid and uncoordinated urbanization often leads to new habitats for filaria vectors.22,23 Especially poor * Address correspondence to Jürg Utzinger, Department of Public design and lack of maintenance of infrastructures for drainage Health and Epidemiology, Swiss Tropical Institute, CH-4002 Basel, of sewage and storm water, waste-water management, water Switzerland. E-mail: [email protected] storage, and urban subsistence agriculture can facilitate the 523 524 ERLANGER AND OTHERS proliferation of mosquitoes, including those transmitting fi- that chronic parasitic diseases, including LF, could be used as laria. Although the proportion of urban dwellers in the least viable health indicators for monitoring poverty alleviation, as developed countries was only 27% in 1975, it rose to 40% in the root ecological causes of these health conditions depend 2000 and is predicted to further increase. Nearly 50% of the on poor sanitation, inadequate water supply and lack of vec- world’s urban population is concentrated in Asia. Currently, tor control measures.27 the annual growth rate in Asian cities is 2.7%.24 This implies Search strategies and selection criteria. With the aim of that in the future, an increasing number of habitats with or- identifying all published studies that examined the effect of ganically polluted water will be available for Culex vectors. water resource development and management on the fre- The objectives of the systematic literature review presented quency and transmission dynamics of LF, we carried out a in this paper were (i) to assess the current size of the popu- systematic literature review. Particular consideration was lation at risk of LF with particular consideration of water given to publications that contained specifications on (i) en- resource development and management, both in rural and tomological transmission parameters, abundance of vector urban settings, and (ii) to assess the effect of these ecological populations, microfilaria infection prevalence and rates of transformations on the frequency and transmission dynamics clinical manifestations as a result of water resource develop- of LF. Our working hypothesis was that environmental ment, and (ii) studies that compared sites where environmen- changes resulting from water resource development and man- tal changes occurred with ecologically similar settings where agement adversely affect vector frequencies, filaria transmis- no water resource developments were implemented. sion, prevalence of infection, and clinical occurrence of LF. As a first step, we performed computer-aided searches us- These issues are of direct relevance for GPELF and evidence- ing the National Library of Medicine’s PubMed database, as based policy-making, and for integrated vector management well as BIOSIS Previews, Cambridge Scientific Abstracts In- programs and optimal resource allocation for disease control ternet Database Service, and ISI Web of Science. We were more generally. interested in citations published as far back as 1945. The fol- lowing keywords (medical subject headings and technical terms) were used: “lymphatic filariasis” in combination with MATERIALS AND METHODS “water,”“water management,”“reservoir(s),”“irrigation,” “dam(s),”“pool(s),”“sanitation,”“ecological transforma- tion,” and “urbanization.” No restrictions were placed on lan- Contextual determinants and estimation of population at guage of publication. risk in endemic countries. As a first step, we outlined the