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Global eradication of lymphatic filariasis: the value of chronic disease control in parasite elimination programmes.

ABSTRACT: The ultimate goal of the global programme against lymphatic filariasis is eradication through irrevocable cessation of transmission using 4 to 6 years of annual single dose mass drug administration. The costs of eradication, managerial impediments to executing national control programmes, and scientific uncertainty about transmission endpoints, are challenges to the success of this effort, especially in areas of high endemicity where financial resources are limited. We used a combined analysis of empirical community data describing the association between infection and chronic disease prevalence, mathematical modelling, and economic analyses to identify and evaluate the feasibility of setting an infection target level at which the chronic pathology attributable to lymphatic filariasis--lymphoedema of the extremities and hydroceles--becomes negligible in the face of continuing transmission as a first stage option in achieving the elimination of this parasitic disease. The results show that microfilaria prevalences below a threshold of 3.55% at a blood sampling volume of 1 ml could constitute readily achievable and sustainable targets to control lymphatic filarial disease. They also show that as a result of the high marginal cost of curing the last few individuals to achieve elimination, maximal benefits can occur at this threshold. Indeed, a key finding from our coupled economic and epidemiological analysis is that when initial uncertainty regarding eradication occurs and prospects for resolving this uncertainty over time exist, it is economically beneficial to adopt a flexible, sequential, eradication strategy based on controlling chronic disease initially.

SUBMITTER: Michael E

PROVIDER: S-EPMC2490717 | biostudies-literature | 2008 Aug

REPOSITORIES: biostudies-literature

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Global eradication of lymphatic filariasis: the value of chronic disease control in parasite elimination programmes.

Michael Edwin E Malecela Mwele N MN Zervos Mihail M Kazura James W JW

PloS one 20080813 8

The ultimate goal of the global programme against lymphatic filariasis is eradication through irrevocable cessation of transmission using 4 to 6 years of annual single dose mass drug administration. The costs of eradication, managerial impediments to executing national control programmes, and scientific uncertainty about transmission endpoints, are challenges to the success of this effort, especially in areas of high endemicity where financial resources are limited. We used a combined analysis o ...[more]

PMID: 18698350

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Project description:BackgroundMathematical models are increasingly being used to evaluate strategies aiming to achieve the control or elimination of parasitic diseases. Recently, owing to growing realization that process-oriented models are useful for ecological forecasts only if the biological processes are well defined, attention has focused on data assimilation as a means to improve the predictive performance of these models.Methodology and principal findingsWe report on the development of an analytical framework to quantify the relative values of various longitudinal infection surveillance data collected in field sites undergoing mass drug administrations (MDAs) for calibrating three lymphatic filariasis (LF) models (EPIFIL, LYMFASIM, and TRANSFIL), and for improving their predictions of the required durations of drug interventions to achieve parasite elimination in endemic populations. The relative information contribution of site-specific data collected at the time points proposed by the WHO monitoring framework was evaluated using model-data updating procedures, and via calculations of the Shannon information index and weighted variances from the probability distributions of the estimated timelines to parasite extinction made by each model. Results show that data-informed models provided more precise forecasts of elimination timelines in each site compared to model-only simulations. Data streams that included year 5 post-MDA microfilariae (mf) survey data, however, reduced each model's uncertainty most compared to data streams containing only baseline and/or post-MDA 3 or longer-term mf survey data irrespective of MDA coverage, suggesting that data up to this monitoring point may be optimal for informing the present LF models. We show that the improvements observed in the predictive performance of the best data-informed models may be a function of temporal changes in inter-parameter interactions. Such best data-informed models may also produce more accurate predictions of the durations of drug interventions required to achieve parasite elimination.SignificanceKnowledge of relative information contributions of model only versus data-informed models is valuable for improving the usefulness of LF model predictions in management decision making, learning system dynamics, and for supporting the design of parasite monitoring programmes. The present results further pinpoint the crucial need for longitudinal infection surveillance data for enhancing the precision and accuracy of model predictions of the intervention durations required to achieve parasite elimination in an endemic location.

Project description:BackgroundThe prevalence of Wuchereria bancrofti, which causes lymphatic filariasis (LF) in The Gambia was among the highest in Africa in the 1950s. However, surveys conducted in 1975 and 1976 revealed a dramatic decline in LF endemicity in the absence of mass drug administration (MDA). The decline in prevalence was partly attributed to a significant reduction in mosquito density through the widespread use of insecticidal nets. Based on findings elsewhere that vector control alone can interrupt LF, we asked the question in 2013 whether the rapid scale up in the use of insecticidal nets in The Gambia had interrupted LF transmission.Methodology/principal findingWe present here the results of three independently designed filariasis surveys conducted over a period of 17 years (1997-2013), and involving over 6000 subjects in 21 districts across all administrative divisions in The Gambia. An immunochromatographic (ICT) test was used to detect W. bancrofti antigen during all three surveys. In 2001, tests performed on stored samples collected between 1997 and 2000, in three divisions, failed to show positive individuals from two divisions that were previously highly endemic for LF, suggesting a decline towards extinction in some areas. Results of the second survey conducted in 2003 showed that LF was no longer endemic in 16 of 21 districts surveyed. The 2013 survey used a WHO recommended LF transmission verification tool involving 3180 6-7 year-olds attending 60 schools across the country. We demonstrated that transmission of W. bancrofti has been interrupted in all 21 districts.ConclusionsWe conclude that LF transmission may have been interrupted in The Gambia through the extensive use of insecticidal nets for malaria control for decades. The growing evidence for the impact of malaria vector control activities on parasite transmission has been endorsed by WHO through a position statement in 2011 on integrated vector management to control malaria and LF.

Project description:The 6th Meeting of the Global Alliance to Eliminate Lymphatic Filariasis (GAELF6) was held 1-3 June, 2010 in Seoul, Korea, with 150 participants from 38 countries. The year 2010 marks the midpoint between the first GAELF meeting, in 2000, and the World Health Organization (WHO) 2020 goal of global elimination of lymphatic filariasis (LF) as a public health problem. The theme of the meeting, "Half-time in LF Elimination: Teaming Up with Neglected Tropical Diseases (NTDs)," reflected significant integration of LF elimination programmes into a comprehensive initiative to control NTDs. Presentations on LF epidemiology, treatment, research, and programmes highlighted both accomplishments and remaining challenges.The WHO strategy to interrupt LF transmission is based on annual mass drug administration (MDA) using two-drug combinations. After mapping the geographic distribution of LF, MDA is implemented for ? 5 years, followed by a period of post-MDA surveillance, and, ultimately, verification of LF elimination. Morbidity management further reduces disease burden.Of 81 countries considered LF-endemic in 2000, 52 (64.2%) have begun MDA; 10 (12.3%) others with low-level transmission are unlikely to require MDA. In 2008, ~695 million people were offered treatment (51.7% of the at-risk population); ~496 million participated. Approximately 22 million people have been protected from LF infection and disease, with savings of ~US $24.2 billion. Morbidity management programmes have been implemented in 27 (33.3%) countries.Significant challenges to LF elimination remain. These include: initiating MDA in the remaining 19 countries that require it; achieving full geographic coverage in countries where MDA has started; finding alternative strategies to address the problem of Loa loa co-endemicity in Central Africa; developing strategies to treat urban populations; initiating and sustaining MDA in settings of armed conflict; developing refined guidelines and procedures for stopping MDA, for post-MDA surveillance, and for verifying the elimination of LF; and integrating morbidity management into all LF elimination programmes. Scientific research and enhanced advocacy for NTDs remain critical for addressing these challenges.GAELF6 was characterized by enthusiasm and recognition that "teaming up with NTDs" offers opportunities for new partnerships, fresh perspectives, enhanced advocacy, and greater programmatic integration in a rapidly changing global health environment.

Project description:BackgroundLymphatic filariasis (LF) is a major public health problem in the Pacific Region, including in Fiji. Through transmission by the mosquito vector Aedes, Fiji has suffered the burden of remaining endemic with LF despite efforts at elimination prior to 1999. In the year 1999, Fiji agreed to take part in the Pacific Programme for Elimination of LF (PacELF) and the Global Programme to Eliminate LF.MethodsThis study reviewed and collated past data on LF in Fiji between 1997 and 2007. Sources included published papers as well as unpublished PacELF and WHO program meeting and survey reports. Records were held at Fiji's Department of Health and Medical Services, James Cook University and the WHO office in Suva, Fiji.ResultsBaseline surveys between 1997 and 2002 showed that Fiji was highly endemic for LF with an estimated 16.6% of the population antigen positive and 6.3% microfilaria positive at that time. Five rounds of annual mass drug administration (MDA) using albendazole and diethylcarbamazine commenced in 2002. Programmatic coverage reported was 58-70% per year, but an independent coverage survey in 2006 in Northern Division after the fifth MDA suggested that actual coverage may have been higher. Monitoring of the program consisted of antigen prevalence surveys in all ages with sentinel and spot check surveys carried out in 2002 (pre MDA), 2004, and 2005, together with knowledge, attitude, and practice surveys. The stop-MDA survey (C survey) in 2007 was a nationwide stratified cluster survey of all ages according to PacELF guidelines, designed to sample by administrative division to identify areas still needing MDA. The national antigen prevalence in 2007 was reduced by more than a third to 9.5%, ranging from 0.9% in Western Division to 15.4% in Eastern Division, while microfilaria prevalence was reduced by almost four-fifths to 1.4%. Having not reached the target threshold of 1% prevalence in all ages, Fiji wisely decided to continue MDA after 2007 but to move from nationwide implementation to four (later five) separate evaluation units with independent timelines using global guidelines, building on program experience to put more emphasis on increasing coverage through prioritized communication strategies, community participation, and morbidity alleviation.ConclusionFiji conducted nationwide MDA for LF annually between 2002 and 2006, monitored by extensive surveys of prevalence, knowledge, and coverage. From a high baseline prevalence in all divisions, large reductions in overall and age-specific prevalence were achieved, especially in the prevalence of microfilariae, but the threshold for stopping MDA was not reached. Fiji has a large rural and geographically widespread population, program management was not consistent over this period, and coverage achieved was likely not optimal in all areas. After learning from these many challenges and activities, Fiji was able to build on the progress achieved and the heterogeneity observed in prevalence to realign towards a more stratified and improved program after 2007. The information presented here will assist the country to progress towards validating elimination in subsequent years.

Project description:BackgroundThe Global Programme to Eliminate Lymphatic Filariasis (GPELF) was launched in response to the call proposed at the 50th World Health Assembly. The goal of the GPELF is to ensure that all the countries where the disease is endemic would have been transmission-free or would have entered post-intervention mass drug administration (MDA) surveillance by 2020. However, several countries are still not on track to discontinue MDA as planned. Thus, issues remain regarding the achievement of stated goals and how to effectively monitor the disease in the post-control and post-elimination phases.Main textChina was once a lymphatic filariasis (LF) endemic country with heavy disease burden. There were three milestones in the LF control phase of China, including: the proposal that the major focus of the control strategy should be on infectious sources; the three regimens of diethylcarbamazine (DEC) administration according to LF endemic extent; and the establishment of the threshold for LF transmission interruption. It has been ten years since China entered the post-elimination stage (declaration of LF elimination in China was in 2007). Two schemes and a diagnostic criterion were issued to guide all levels of disease control and prevention workers that conduct LF surveillance, as well as those caring for chronic filariasis patients. Regular training courses are held to maintain LF control skills in grass-root institutions. The Notifiable Diseases Reporting System, which included LF in 2004, plays an important role in LF post-elimination surveillance. Until now, no resurgence of LF cases has been detected, except for LF residue foci being found in Fuchuan County of the Guangxi Zhuang Autonomous Region. To confirm that transmission is no longer achievable after a decade since the declaration of LF elimination in China, it is expected within the next two years a transmission assessment survey, conducted in previous LF-endemic areas.ConclusionsDEC-fortified salt can help accelerate the progress of GPELF before the sprite phase. Sophisticated diagnostic criteria, systematic surveillance regimes, the Direct Network Report system, and regular trainings can effectively prevent the recrudescence of LF during surveillance phases.

Dataset Information

Global eradication of lymphatic filariasis: the value of chronic disease control in parasite elimination programmes.

Publications

Global eradication of lymphatic filariasis: the value of chronic disease control in parasite elimination programmes.

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