Cessation of mass drug administration for lymphatic filariasis in Zanzibar in 2006: was transmission interrupted?

The long road to schistosomiasis elimination in Zanzibar: A systematic review covering 100 years of research, interventions and control milestones

Zanzibar is among the few places in sub-Saharan Africa where interruption of Schistosoma transmission seems an achievable goal. Our systematic review identifies and discusses milestones in schistosomiasis research, control and elimination efforts in Zanzibar over the past 100 years. The search in online databases, libraries, and the World Health Organization Archives revealed 153 records published between May 1928 and August 2022. The content of records was summarised to highlight the pivotal work leading towards urogenital schistosomiasis elimination and remaining research gaps. The greatest achievement following 100 years of schistosomiasis interventions and research is undoubtedly the improved health of Zanzibaris, exemplified by the reduction in Schistosoma haematobium prevalence from>50% historically down to<5% in 2020, and the absence of severe morbidities. Experiences from Zanzibar have contributed to global schistosomiasis guidelines, whilst also revealing challenges that impede progression towards elimination. Challenges include: transmission heterogeneity requiring micro-targeting of interventions, post-treatment recrudescence of infections in transmission hotspots, biological complexity of intermediate host snails, emergence of livestock Schistosoma species complicating surveillance whilst creating the risk for interspecies hybridisation, insufficient diagnostics performance for light intensity infections and female genital schistosomiasis, and a lack of acceptable sanitary alternatives to freshwater bodies. Our analysis of the past revealed that much can be achieved in the future with practical implementation of integrated interventions, alongside operational research. With continuing national and international commitments, interruption of S. haematobium transmission across both islands is within reach by 2030, signposting the future demise of urogenital schistosomiasis across other parts of sub-Saharan Africa.

Potential drivers for schistosomiasis persistence: Population genetic analyses from a cluster-randomized urogenital schistosomiasis elimination trial across the Zanzibar islands

The World Health Organization's revised NTD Roadmap and the newly launched Guidelines target elimination of schistosomiasis as a public health problem in all endemic areas by 2030. Key to meeting this goal is elucidating how selective pressures imposed by interventions shape parasite populations. Our aim was to identify any differential impact of a unique cluster-randomized tri-armed elimination intervention (biannual mass drug administration (MDA) applied alone or in association with either mollusciciding (snail control) or behavioural change interventions) across two Zanzibarian islands (Pemba and Unguja) on the population genetic composition of Schistosoma haematobium over space and time. Fifteen microsatellite loci were used to analyse individual miracidia collected from infected individuals across islands and intervention arms at the start (2012 baseline: 1,522 miracidia from 176 children; 303 from 43 adults; age-range 6-75, mean 12.7 years) and at year 5 (2016: 1,486 miracidia from 146 children; 214 from 25 adults; age-range 9-46, mean 12.4 years). Measures of genetic diversity included allelic richness (Ar), Expected (He) and Observed heterozygosity (Ho), inbreeding coefficient (FST), parentage analysis, estimated worm burden, worm fecundity, and genetic sub-structuring. There was little evidence of differential selective pressures on population genetic diversity, inbreeding or estimated worm burdens by treatment arm, with only the MDA+snail control arm within Unguja showing trends towards reduced diversity and altered inbreeding over time. The greatest differences overall, both in terms of parasite fecundity and genetic sub-structuring, were observed between the islands, consistent with Pemba's persistently higher mean infection intensities compared to neighbouring Unguja, and within islands in terms of infection hotspots (across three definitions). These findings highlight the important contribution of population genetic analyses to elucidate extensive genetic diversity and biological drivers, including potential gene-environmental factors, that may override short term selective pressures imposed by differential disease control strategies. Trial Registration: ClinicalTrials.gov ISRCTN48837681.

Post-Treatment Surveillance for Lymphatic Filariasis in Plateau and Nasarawa States, Nigeria: Results of Transmission Assessment Surveys

Following the halt of mass drug administration (MDA) for lymphatic filariasis (LF), the WHO recommends at least 4 years of post-treatment surveillance (PTS) to confirm that transmission recrudescence or importation does not occur. The primary means of evaluation during PTS is repeated transmission assessment surveys (TASs) conducted at 2- to 3-year intervals after TAS-1 stop-MDA surveys. This study reports the results of TAS-2 and TAS-3 surveys in Plateau and Nasarawa states (pop. 6.9 million) of Nigeria divided into a minimum of seven evaluation units (EUs) per TAS. A total of 26,536 first- and second-year primary school children (approximately 6–7 years old) were tested for circulating filarial antigen (CFA) between 2014 and 2017. Of 12,313 children tested in TAS-2 surveys, only five (0.04%) were CFA positive, with no more than two positive samples from any one EU, which was below the critical value of 20 per EU. Of 14,240 children tested in TAS-3 surveys, none (0%) were CFA positive. These results indicate that LF transmission remains below sustainable transmission levels and suggest that elimination of transmission has been achieved in Plateau and Nasarawa, Nigeria.

Molecular xenomonitoring as a post-MDA surveillance tool for global programme to eliminate lymphatic filariasis: Field validation in an evaluation unit in India

Background

Lymphatic filariasis (LF) is targeted for elimination by the year 2020. As of 2017, 67 of the 72 endemic countries have implemented annual Mass Drug Administration (MDA) for interrupting LF transmission. Transmission Assessment Survey (TAS) is the recommended protocol to evaluate the impact of MDA and to decide when to stop MDA in an Evaluation Unit (EU, population ≤2 million). As the human infection levels go down with repeated MDA rounds, it becomes a challenge to select the appropriate survey methods to assess transmission interruption. This study validates a standard protocol for molecular xenomonitoring of infection in vectors (MX) at an EU as a complementary tool for TAS to stop MDA and its utility for post-MDA or post-validation surveillance.

Methodology

The study was conducted in Cuddalore district, Tamil Nadu, India, which was found eligible for TAS after 15 annual rounds of MDA (4 with DEC alone and 11 with DEC plus albendazole). The district was divided into two EUs as per the TAS protocol and one EU was randomly selected for the study. A two-stage cluster design vector sampling, developed and validated at a sub-district level, was implemented in 30 randomly selected clusters in the EU. Female Culex quinquefasciatus were collected placing gravid traps overnight (1800–0600 hrs) inside the premises of systematically selected households. Pools of 20–25 blood-fed, semi-gravid and gravid Cx. quinquefasciatus were subjected to real-time quantitative PCR (polymerase chain reaction) assay for detecting Wuchereria bancrofti DNA. Pool infection rate (% of pools positive for W. bancrofti DNA), and the estimated prevalence of W. bancrofti DNA in mosquitoes and its 95% confidence interval were calculated. Additionally, in these 30 clusters, microfilaria (Mf) survey among individuals >5 years old was carried out. School-based TAS was conducted using Immunochromatographic Card Test (ICT) in the EU. Prepared itemized cost-menu for different cost components of MX survey and TAS were estimated and compared.

Results

MX survey showed that only 11 (3.1%) of the 358 pools (8850 Cx.quinquefasciatus females), collected from 30 clusters, were found positive for W. bancrofti DNA. The estimated vector infection rate was 0.13% (95% CI: 0.07–0.22%), below the provisional threshold (0.25%) for transmission interruption. Of 1578 children tested in the TAS, only four (0.25%) were positive for filarial antigenemia, and it is well below the critical cut-off (18 positives) for stopping MDA. Among 9804 persons tested in the 30 clusters, only four were found positive for Mf (0.04%; 95% CI: 0.01–0.1%). The Mf-prevalence was <1% threshold for transmission interruption in humans. The estimated costs for TAS and MX per EU were $14,104 USD and $14,259 USD respectively.

Conclusions

The result of MX protocol was in good agreement with that of TAS, providing evidence to recommend MX as a complementary tool to TAS to decide on stopping MDA. MX can also be a potential surveillance tool for post-MDA and post-validation phases as it could detect sites with residual infection and risk of resurgence of transmission. MX is economically feasible as its cost is slightly higher than that of TAS.

Lymphatic filariasis (LF), commonly known as “elephantiasis” is caused by filarial parasites and transmitted among humans by mosquitoes. This parasitic infection results in chronic diseases such as swelling of limbs and hydrocele. Global programme to eliminate lymphatic filariasis (GPELF), launched by the World Health Organization (WHO) in 2000 endorsed the mass treatment of all the people above 2 years of age in the endemic areas with a single dose of anti-filarial drugs administered annually for a minimum period of 5 years. WHO also recommended transmission assessment survey (TAS) protocol to assess the impact of mass treatment and to decide on stopping mass treatment. The protocol aims at screening young children who were born after the mass treatment for filarial infection. If the number of infected children is smaller than the pre-defined number, mass treatment can be stopped. The same protocol is followed for periodical assessment to verify whether there are any new infections. Alternatively, vector infection levels by molecular xenomonitoring (MX, detection of parasite DNA in the mosquitoes) can be used to verify whether there are any infected mosquitoes. This tool has been applied in many studies and there is a provisionally established mosquito infection threshold level (0.25%) below which transmission is interrupted. This can be an alternative tool for TAS. We validated this method at district level by collecting filariasis transmitting mosquitoes from 30 villages/wards and compared the results with those of TAS. There was good agreement between the decisions based on TAS and MX in our study. Though in the EU both vector and human infection levels were below their respective threshold levels, the mosquito infection in individual sites was above the threshold, indicating residual hotspots and risk of resurgence. In addition, we estimated the cost of conducting MX and TAS for their economic feasibility and found that the cost of MX is only marginally higher than that of school-based TAS. Thus, our study results provide recommendations to use MX as a tool complementary to TAS (i) for taking a decision on stopping MDA, (ii) for monitoring post-MDA and post-validation surveillance programme, and (iii) for remapping areas to initiate MDA.

De novo Assembly of the Brugia malayi Genome Using Long Reads from a Single MinION Flowcell

Filarial nematode infections cause a substantial global disease burden. Genomic studies of filarial worms can improve our understanding of their biology and epidemiology. However, genomic information from field isolates is limited and available reference genomes are often discontinuous. Single molecule sequencing technologies can reduce the cost of genome sequencing and long reads produced from these devices can improve the contiguity and completeness of genome assemblies. In addition, these new technologies can make generation and analysis of large numbers of field isolates feasible. In this study, we assessed the performance of the Oxford Nanopore Technologies MinION for sequencing and assembling the genome of Brugia malayi, a human parasite widely used in filariasis research. Using data from a single MinION flowcell, a 90.3 Mb nuclear genome was assembled into 202 contigs with an N50 of 2.4 Mb. This assembly covered 96.9% of the well-defined B. malayi reference genome with 99.2% identity. The complete mitochondrial genome was obtained with individual reads and the nearly complete genome of the endosymbiotic bacteria Wolbachia was assembled alongside the nuclear genome. Long-read data from the MinION produced an assembly that approached the quality of a well-established reference genome using comparably fewer resources.

Progress towards lymphatic filariasis elimination in Ghana from 2000-2016: Analysis of microfilaria prevalence data from 430 communities

BACKGROUND

Ghana started its national programme to eliminate lymphatic filariasis (LF) in 2000, with mass drug administration (MDA) with ivermectin and albendazole as main strategy. We review the progress towards elimination that was made by 2016 for all endemic districts of Ghana and analyze microfilaria (mf) prevalence from sentinel and spot-check sites in endemic districts.

METHODS

We reviewed district level data on the history of MDA and outcomes of transmission assessment surveys (TAS). We further collated and analyzed mf prevalence data from sentinel and spot-check sites.

RESULTS

MDA was initiated in 2001-2006 in all 98 endemic districts; by the end of 2016, 81 had stopped MDA after passing TAS and after an average of 11 rounds of treatment (range 8-14 rounds). The median reported coverage for the communities was 77-80%. Mf prevalence survey data were available for 430 communities from 78/98 endemic districts. Baseline mf prevalence data were available for 53 communities, with an average mf prevalence of 8.7% (0-45.7%). Repeated measurements were available for 78 communities, showing a steep decrease in mean mf prevalence in the first few years of MDA, followed by a gradual further decline. In the 2013 and 2014 surveys, 7 and 10 communities respectively were identified with mf prevalence still above 1% (maximum 5.6%). Fifteen of the communities above threshold are all within districts where MDA was still ongoing by 2016.

CONCLUSIONS

The MDA programme of the Ghana Health Services has reduced mf prevalence in sentinel sites below the 1% threshold in 81/98 endemic districts in Ghana, yet 15 communities within 13 districts (MDA ongoing by 2016) had higher prevalence than this threshold during the surveys in 2013 and 2014. These districts may need to intensify interventions to achieve the WHO 2020 target.

Mapping and monitoring for a lymphatic filariasis elimination program: a systematic review

Lymphatic filariasis (LF) is targeted for elimination by the year 2020. The Global Programme for Elimination of LF (GPELF) aims to achieve elimination by interrupting transmission through annual mass drug administration (MDA) of albendazole with ivermectin or diethylcarbamazine. The program has successfully eliminated the disease in 11 of the 72 endemic countries, putting in enormous efforts on systematic planning and implementation of the strategy. Mapping areas endemic for LF is a pre-requisite for implementing MDA, monitoring and evaluation are the components of programme implementation. This review was undertaken to assess how the mapping and impact monitoring activities have evolved to become more robust over the years and steered the LF elimination programme towards its goal. The findings showed that the WHO recommended mapping strategy aided 17 countries to delimit, plan and implement MDA in only those areas endemic for LF thereby saving resources. Availability of serological tools for detecting infection in humans (antigen/antibody assays) and molecular xenomonitoring (MX) in vectors greatly facilitated programme monitoring and evaluation in endemic countries. Results of this review are discussed on how these existing mapping and monitoring procedures can be used for re-mapping of unsurveyed and uncertain areas to ensure there is no resurgence during post-MDA surveillance. Further the appropriateness of the tests (Microfilaria (Mf)/antigenemia (Ag)/antibody(Ab) surveys in humans or MX of vectors for infection) used currently for post-MDA surveillance and their role in the development of a monitoring and evaluation strategy for the recently WHO recommended triple drug regimen in MDA for accelerated LF elimination are discussed.

Understanding heterogeneities in mosquito-bite exposure and infection distributions for the elimination of lymphatic filariasis

It is well known that individuals in the same community can be exposed to a highly variable number of mosquito bites. This heterogeneity in bite exposure has consequences for the control of vector-borne diseases because a few people may be contributing significantly to transmission. However, very few studies measure sources of heterogeneity in a way which is relevant to decision-making. We investigate the relationship between two classic measures of heterogeneity, spatial and individual, within the context of lymphatic filariasis, a parasitic mosquito-borne disease. Using infection and mosquito-bite data for five villages in Papua New Guinea, we measure biting characteristics to model what impact bed-nets have had on control of the disease. We combine this analysis with geospatial modelling to understand the spatial relationship between disease indicators and nightly mosquito bites. We found a weak association between biting and infection heterogeneity within villages. The introduction of bed-nets increased biting heterogeneity, but the reduction in mean biting more than compensated for this, by reducing prevalence closer to elimination thresholds. Nightly biting was explained by a spatial heterogeneity model, while parasite load was better explained by an individual heterogeneity model. Spatial and individual heterogeneity are qualitatively different with profoundly different policy implications.

Determinants of transmission hotspots and filarial infection in households after eight rounds of mass drug administration in India

OBJECTIVES

Lymphatic filariasis (LF) elimination through mass drug administration (MDA) of DEC and albendazole have resulted in very low levels of infection in most endemic districts in India. But small pockets with residual microfilaraemia in the community and antigeneamia in children ('hotspots') are a cause of concern. We aimed to identify the determinants of such transmission hotspots and filarial infection in households using data from 33 communities.

METHODS

The filariasis vector Culex quinquefasciatus was collected from 627 randomly selected households using gravid traps. Parallel data on environmental, entomological, demographical, socio-economical and behavioural factors were analysed to identify the determinants of hotspots and household-level infection.

RESULTS

Hotspots and non-hotspots did not differ significantly in terms of socio-economical and behavioural aspects, but did differ in terms of demographical and environmental factors. Logistic regression revealed that tiled and concrete houses increased the risk of an area being a hotspot by 2.0 and 2.9 times respectively. Presence of Culex breeding habitats was significantly associated with elevated risk of being a hotspot. Proximity of U-drains to a house increased the risk of filarial infection 5.8 times.

CONCLUSIONS

An environment suitable to Culex breeding influences continued transmission despite eight rounds of MDA, particularly in hotspots. Proximity to U-drains increases the risk of infection in households. Implementing localised vector control measures may help interrupt low-level transmission, thereby reducing the risk of resurgence in the absence of MDA.

Lymphatic filariasis control in Tanzania: infection, disease perceptions and drug uptake patterns in an endemic community after multiple rounds of mass drug administration

BACKGROUND

Lymphatic filariasis (LF) control in most countries of sub-Saharan Africa is based on annual mass drug administration (MDA) with a combination of ivermectin and albendazole, in order to interrupt transmission. However, attaining and maintaining high treatment coverage has been a challenge in many LF control programmes. This study was designed to elucidate reasons for continued transmission of LF in an endemic area of Tanga, northeastern Tanzania, where control activities based on MDA had been in place for eight years by the time of this study in 2012.

METHODS

A cross-sectional questionnaire survey was conducted in three sentinel villages used for monitoring the impact of MDA on LF transmission. A total of 747 individuals were interviewed, out of which 172 (23.0%), 27 (3.6%) and 49 (6.5%) had been shown to have circulating filarial antigens (CFA), microfilaraemia (MF) and LF gross lesions, respectively, prior to the interviews.

RESULTS

The interviewed population had a mean age of 33.7 years and a male to female ratio of 0.8. Males, individuals aged 30 years and above, peasants/fishermen and recent immigrants to the study communities were significantly more affected (CFA, MF and/ or LF gross lesions) than the other population groups. However, drug uptake rates were not significantly different between LF affected (those with CFA, MF and/ or LF gross lesions) and non-affected individuals. Likewise, drug uptake rates were not significantly different across different demographic parameters of the study population, some of which differed significantly in the level of infection. Moreover, it was found that misconceptions on how LF can be acquired were still evident, linking its transmission to witchcraft, heredity and sexual behaviour.

CONCLUSIONS

The findings indicated that misconceptions about LF and its transmission still existed despite eight years of control activities in the area. Improved communication on the rationale of MDA and an enhanced drug delivery strategy that is adapted to the local settings and targeting important demographic groups that serve as reservoir of infection will help in reaching the elimination target within a reasonable timeframe.

Detecting and confirming residual hotspots of lymphatic filariasis transmission in American Samoa 8 years after stopping mass drug administration

The Global Programme to Eliminate Lymphatic Filariasis (LF) aims to eliminate the disease as a public health problem by 2020 by conducting mass drug administration (MDA) and controlling morbidity. Once elimination targets have been reached, surveillance is critical for ensuring that programmatic gains are sustained, and challenges include timely identification of residual areas of transmission. WHO guidelines encourage cost-efficient surveillance, such as integration with other population-based surveys. In American Samoa, where LF is caused by Wuchereria bancrofti, and Aedes polynesiensis is the main vector, the LF elimination program has made significant progress. Seven rounds of MDA (albendazole and diethycarbamazine) were completed from 2000 to 2006, and Transmission Assessment Surveys were passed in 2010/2011 and 2015. However, a seroprevalence study using an adult serum bank collected in 2010 detected two potential residual foci of transmission, with Og4C3 antigen (Ag) prevalence of 30.8% and 15.6%. We conducted a follow up study in 2014 to verify if transmission was truly occurring by comparing seroprevalence between residents of suspected hotspots and residents of other villages. In adults from non-hotspot villages (N = 602), seroprevalence of Ag (ICT or Og4C3), Bm14 antibody (Ab) and Wb123 Ab were 1.2% (95% CI 0.6-2.6%), 9.6% (95% CI 7.5%-12.3%), and 10.5% (95% CI 7.6-14.3%), respectively. Comparatively, adult residents of Fagali'i (N = 38) had significantly higher seroprevalence of Ag (26.9%, 95% CI 17.3-39.4%), Bm14 Ab (43.4%, 95% CI 32.4-55.0%), and Wb123 Ab 55.2% (95% CI 39.6-69.8%). Adult residents of Ili'ili/Vaitogi/Futiga (N = 113) also had higher prevalence of Ag and Ab, but differences were not statistically significant. The presence of transmission was demonstrated by 1.1% Ag prevalence (95% CI 0.2% to 3.1%) in 283 children aged 7-13 years who lived in one of the suspected hotspots; and microfilaraemia in four individuals, all of whom lived in the suspected hotspots, including a 9 year old child. Our results provide field evidence that integrating LF surveillance with other surveys is effective and feasible for identifying potential hotspots, and conducting surveillance at worksites provides an efficient method of sampling large populations of adults.

How much will it cost to eradicate lymphatic filariasis? An analysis of the financial and economic costs of intensified efforts against lymphatic filariasis

INTRODUCTION

Lymphatic filariasis (LF), a neglected tropical disease (NTD) preventable through mass drug administration (MDA), is one of six diseases deemed possibly eradicable. Previously we developed one LF elimination scenario, which assumes MDA scale-up to continue in all countries that have previously undertaken MDA. In contrast, our three previously developed eradication scenarios assume all LF endemic countries will undertake MDA at an average (eradication I), fast (eradication II), or instantaneous (eradication III) rate of scale-up. In this analysis we use a micro-costing model to project the financial and economic costs of each of these scenarios in order to provide evidence to decision makers about the investment required to eliminate and eradicate LF.

METHODOLOGY/KEY FINDINGS

Costing was undertaken from a health system perspective, with all results expressed in 2012 US dollars (USD). A discount rate of 3% was applied to calculate the net present value of future costs. Prospective NTD budgets from LF endemic countries were reviewed to preliminarily determine activities and resources necessary to undertake a program to eliminate LF at a country level. In consultation with LF program experts, activities and resources were further reviewed and a refined list of activities and necessary resources, along with their associated quantities and costs, were determined and grouped into the following activities: advocacy and communication, capacity strengthening, coordination and strengthening partnerships, data management, ongoing surveillance, monitoring and supervision, drug delivery, and administration. The costs of mapping and undertaking transmission assessment surveys and the value of donated drugs and volunteer time were also accounted for. Using previously developed scenarios and deterministic estimates of MDA duration, the financial and economic costs of interrupting LF transmission under varying rates of MDA scale-up were then modelled using a micro-costing approach. The elimination scenario, which includes countries that previously undertook MDA, is estimated to cost 929 million USD (95% Credible Interval: 884m-972m). Proceeding to eradication is anticipated to require a higher financial investment, estimated at 1.24 billion USD (1.17bn-1.30bn) in the eradication III scenario (immediate scale-up), with eradication II (intensified scale-up) projected at 1.27 billion USD (1.21bn-1.33bn), and eradication I (slow scale-up) estimated at 1.29 billion USD (1.23bn-1.34bn). The economic costs of the eradication III scenario are estimated at approximately 7.57 billion USD (7.12bn-7.94bn), while the elimination scenario is projected to have an economic cost of 5.21 billion USD (4.91bn-5.45bn). Countries in the AFRO region will require the greatest investment to reach elimination or eradication, but also stand to gain the most in cost savings. Across all scenarios, capacity strengthening and advocacy and communication represent the greatest financial costs, whereas mapping, post-MDA surveillance, and administration comprise the least.

CONCLUSIONS/SIGNIFICANCE

Though challenging to implement, our results indicate that financial and economic savings are greatest under the eradication III scenario. Thus, if eradication for LF is the objective, accelerated scale-up is projected to be the best investment.

Side Benefits of Mass Drug Administration for Lymphatic Filariasis on Strongyloides stercoralis Prevalence on Pemba Island, Tanzania

Strongyloides stercoralis, although endemic in many countries, is not included in helminth control programs. Few data are available on the prevalence and morbidity linked to this infection. We compared data from two studies conducted in 1998 and 2013 on Pemba Island, Tanzania, involving 525 and 509 schoolchildren, respectively. In 1998, the diagnostic method used was Harada Mori, whereas in 2013 diagnosis was made by both Koga agar plate and Baermann methods. The prevalence registered was 41% in 1998 and 7% in 2013. This data suggest that the prevalence of S. stercoralis on Pemba was significantly reduced 7 years after the last ivermectin administration for preventive chemotherapy and underlines the importance and impact of large-scale preventive chemotherapy, which often goes beyond its actual target. Preventive chemotherapy with ivermectin should be recommended in areas where S. stercoralis is endemic.

The significant scale up and success of Transmission Assessment Surveys 'TAS' for endgame surveillance of lymphatic filariasis in Bangladesh: One step closer to the elimination goal of 2020

BACKGROUND

Bangladesh had one of the highest burdens of lymphatic filariasis (LF) at the start of the Global Programme to Eliminate Lymphatic Filariasis (GPELF) with an estimated 70 million people at risk of infection across 34 districts. In total 19 districts required mass drug administration (MDA) to interrupt transmission, and 15 districts were considered low endemic. Since 2001, the National LF Programme has implemented MDA, reduced prevalence, and been able to scale up the WHO standard Transmission Assessment Survey (TAS) across all endemic districts as part of its endgame surveillance strategy. This paper presents TAS results, highlighting the momentous geographical reduction in risk of LF and its contribution to the global elimination target of 2020.

METHODOLOGY/PRINCIPAL FINDINGS

The TAS assessed primary school children for the presence of LF antigenaemia in each district (known as an evaluation unit-EU), using a defined critical cut-off threshold (or 'pass') that indicates interruption of transmission. Since 2011, a total of 59 TAS have been conducted in 26 EUs across the 19 endemic MDA districts (99,148 students tested from 1,801 schools), and 22 TAS in the 15 low endemic non-MDA districts (36,932 students tested from 663 schools). All endemic MDA districts passed TAS, except in Rangpur which required two further rounds of MDA. In total 112 students (male n = 59; female n = 53), predominately from the northern region of the country were found to be antigenaemia positive, indicating a recent or current infection. However, the distribution was geographically sparse, with only two small focal areas showing potential evidence of persistent transmission.

CONCLUSIONS/SIGNIFICANCE

This is the largest scale up of TAS surveillance activities reported in any of the 73 LF endemic countries in the world. Bangladesh is now considered to have very low or no risk of LF infection after 15 years of programmatic activities, and is on track to meet elimination targets. However, it will be essential that the LF Programme continues to develop and maintain a comprehensive surveillance strategy that is integrated into the health infrastructure and ongoing programmes to ensure cost-effectiveness and sustainability.

Urogenital schistosomiasis transmission on Unguja Island, Zanzibar: characterisation of persistent hot-spots

BACKGROUND

Elimination of urogenital schistosomiasis transmission is a priority for the Zanzibar Ministry of Health. Preventative chemotherapy together with additional control interventions have successfully alleviated much of the disease burden. However, a persistently high Schistosoma haematobium prevalence is found in certain areas. Our aim was to characterise and evaluate these persistent "hot-spots" of transmission and reinfection in comparison with low-prevalence areas, to support the intervention planning for schistosomiasis elimination in Zanzibar.

METHODS

Prevalences of S. haematobium were annually determined by a single urine filtration in schoolchildren from 45 administrative areas (shehias) in Unguja in 2012, 2013 and 2014. Coverage data for biannual treatment with praziquantel were available from ministerial databases and internal surveys. Among the 45 shehias, five hot-spot (≥ 15 % prevalence) and two low-prevalence (≤ 5 %) shehias were identified and surveyed in mid-2014. Human-water contact sites (HWCSs) and the presence of S. haematobium-infected and uninfected Bulinus globosus, as well as safe water sources (SWSs) and their reliability in terms of water availability were determined and mapped.

RESULTS

We found no major difference in the treatment coverage between persistent hot-spot and low-prevalence shehias. On average, there were considerably more HWCSs containing B. globosus in hot-spot than in low-prevalence shehias (n = 8 vs n = 2) and also more HWCSs containing infected B. globosus (n = 2 vs n = 0). There was no striking difference in the average abundance of SWSs in hot-spot and low-prevalence shehias (n = 45 vs n = 38) and also no difference when considering SWSs with a constant water supply (average: 62 % vs 62 %). The average number of taps with a constant water supply, however, was lower in hot-spot shehias (n = 7 vs n = 14). Average distances from schools to the nearest HWCS were considerably shorter in hot-spot shehias (n = 229 m vs n = 722 m).

CONCLUSION

The number of HWCSs, their infestation with B. globosus and their distance to schools seem to play a major role for a persistently high S. haematobium prevalence in children. In addition to treatment, increasing access to reliably working taps, targeted snail control at HWCSs near schools and enhanced behaviour change measures are needed to reduce prevalences in hot-spot areas and to finally reach elimination.

TRIAL REGISTRATION

ISRCTN48837681 .

Population genomics of the filarial nematode parasite Wuchereria bancrofti from mosquitoes

Wuchereria bancrofti is a parasitic nematode and the primary cause of lymphatic filariasis--a disease specific to humans. W. bancrofti currently infects over 90 million people throughout the tropics and has been acknowledged by the world health organization as a vulnerable parasite. Current research has focused primarily on the clinical manifestations of disease and little is known about the evolutionary history of W. bancrofti. To improve upon knowledge of the evolutionary history of W. bancrofti, we whole genome sequenced 13 W. bancrofti larvae. We circumvent many of the difficulties of multiple infections by sampling larvae directly from mosquitoes that were experimentally inoculated with infected blood. To begin, we used whole genome data to reconstruct the historical population size. Our results support a history of fluctuating population sizes that can be correlated with human migration and fluctuating mosquito abundances. Next, we reconstructed the putative pedigree of W. bancrofti worms within an infection using the kinship coefficient. We deduced that there are full-sib and half-sib relationships residing within the same larval cohort. Through combined analysis of the mitochondrial and nuclear genomes we concluded that this is likely a results of polyandrous mating, the first time reported for W. bancrofti. Lastly, we scanned the genomes for signatures of natural selection. Annotation of putative selected regions identified proteins that may have aided in a parasitic life style or may have evolved to protect against current drug treatments. We discuss our results in the greater context of understanding the biology of an animal with a unique life history and ecology.

Assessing Lymphatic Filariasis Data Quality in Endemic Communities in Ghana, Using the Neglected Tropical Diseases Data Quality Assessment Tool for Preventive Chemotherapy

Background

The activities of the Global Programme for the Elimination of Lymphatic Filariasis have been in operation since the year 2000, with Mass Drug Administration (MDA) undertaken yearly in disease endemic communities. Information collected during MDA–such as population demographics, age, sex, drugs used and remaining, and therapeutic and geographic coverage–can be used to assess the quality of the data reported. To assist country programmes in evaluating the information reported, the WHO, in collaboration with NTD partners, including ENVISION/RTI, developed an NTD Data Quality Assessment (DQA) tool, for use by programmes. This study was undertaken to evaluate the tool and assess the quality of data reported in some endemic communities in Ghana.

Methods

A cross sectional study, involving review of data registers and interview of drug distributors, disease control officers, and health information officers using the NTD DQA tool, was carried out in selected communities in three LF endemic Districts in Ghana. Data registers for service delivery points were obtained from District health office for assessment. The assessment verified reported results in comparison with recounted values for five indicators: number of tablets received, number of tablets used, number of tablets remaining, MDA coverage, and population treated. Furthermore, drug distributors, disease control officers, and health information officers (at the first data aggregation level), were interviewed, using the DQA tool, to determine the performance of the functional areas of the data management system.

Findings

The results showed that over 60% of the data reported were inaccurate, and exposed the challenges and limitations of the data management system. The DQA tool is a very useful monitoring and evaluation (M&E) tool that can be used to elucidate and address data quality issues in various NTD control programmes.

The Global Programme for the Elimination of Lymphatic Filariasis has been conducting yearly treatment of entire communities in endemic countries since the year 2000. During the treatments various information is collected on the populations, number of medicine tablets distributed and remaining, the number of people treated, etc. that can be used to evaluate the performance of the lymphatic filariasis control programme. For example, information on the number of people treated in a District gives an indication of the success of the programme. In line with this, the World Health Organization in collaboration with other agencies developed a tool for Neglected Tropical Diseases (NTD) to help national control programmes assemble and analyse their data. This study was undertaken to evaluate this tool and the information collected from some endemic communities in Ghana. Community registers were reviewed and personnel involved in drug distribution in the communities were interviewed to collect the necessary information. The results showed that more than half of the data reported in the endemic communities surveyed were inaccurate. It also revealed some weaknesses in the data management and reporting system. The tool, however, is good for identifying and quantifying the magnitude of the challenges encountered in the information management for NTD programmes, especially at peripheral levels.

Praziquantel coverage in schools and communities targeted for the elimination of urogenital schistosomiasis in Zanzibar: a cross-sectional survey

Background

Biannual mass drug administration (MDA) with praziquantel and additional interventions to eliminate urogenital schistosomiasis has been implemented on the Zanzibar islands, United Republic of Tanzania, since 2012. We aimed to assess the coverage of school-based treatment (SBT) and community-wide treatment (CWT), to validate the coverage reported by the Zanzibar Ministry of Health (MoH) and to identify reasons for non-compliance.

Methods

We conducted a post-MDA cross-sectional survey in 93 schools and 92 communities on Pemba and Unguja islands in early 2014, 3–5 months after the last MDA round. Pupils and adults were asked whether they had received and taken the praziquantel treatment provided in the last SBT or CWT, respectively, and the observed and reported coverage were compared. Reasons for non-compliance were recorded in a pretested questionnaire and assessed in qualitative interviews. Urine samples of participants were examined for Schistosoma haematobium eggs with a single urine filtration.

Results

Around 8000 pupils and 4000 adults were included in the analysis. Our survey revealed a SBT coverage of 85.2 % in Pemba and of 86.9 % in Unguja, which was in line with MoH reports from Pemba (84.3 %) and higher than reports from Unguja (63.9 %). However, 15 among the 48 schools surveyed in Unguja had not received SBT. Among the interviewed adults, 53.6 % in Pemba and 64.9 % in Unguja had received praziquantel during CWT, which was less than the 59.0 % and 67.7 %, respectively, indicated by MoH reports. Moreover, only 43.8 % and 54.0 % of adults in Pemba and Unguja, respectively, had taken all the tablets as recommended. The main reasons for not receiving or taking praziquantel were absence during CWT, no drug distributor coming, being busy, fear of adverse events, pregnancy, breastfeeding or feeling healthy.

Conclusion

To increase coverage and compliance in Zanzibar, SBT should target all schools and mobilization, sensitization and implementation of the CWT need to be improved. To reach elimination of urogenital schistosomiasis transmission in Zanzibar and elsewhere, a very high treatment coverage and compliance at national and local level is key and additional control measures such as snail control and behaviour change interventions will need to be implemented area wide.

Trial Registration

ISRCTN48837681.

Modelling the distribution and transmission intensity of lymphatic filariasis in sub-Saharan Africa prior to scaling up interventions: integrated use of geostatistical and mathematical modelling

BACKGROUND

Lymphatic filariasis (LF) is one of the neglected tropical diseases targeted for global elimination. The ability to interrupt transmission is, partly, influenced by the underlying intensity of transmission and its geographical variation. This information can also help guide the design of targeted surveillance activities. The present study uses a combination of geostatistical and mathematical modelling to predict the prevalence and transmission intensity of LF prior to the implementation of large-scale control in sub-Saharan Africa.

METHODS

A systematic search of the literature was undertaken to identify surveys on the prevalence of Wuchereria bancrofti microfilaraemia (mf), based on blood smears, and on the prevalence of antigenaemia, based on the use of an immuno-chromatographic card test (ICT). Using a suite of environmental and demographic data, spatiotemporal multivariate models were fitted separately for mf prevalence and ICT-based prevalence within a Bayesian framework and used to make predictions for non-sampled areas. Maps of the dominant vector species of LF were also developed. The maps of predicted prevalence and vector distribution were linked to mathematical models of the transmission dynamics of LF to infer the intensity of transmission, quantified by the basic reproductive number (R0).

RESULTS

The literature search identified 1267 surveys that provide suitable data on the prevalence of mf and 2817 surveys that report the prevalence of antigenaemia. Distinct spatial predictions arose from the models for mf prevalence and ICT-based prevalence, with a wider geographical distribution when using ICT-based data. The vector distribution maps demonstrated the spatial variation of LF vector species. Mathematical modelling showed that the reproduction number (R0) estimates vary from 2.7 to 30, with large variations between and within regions.

CONCLUSIONS

LF transmission is highly heterogeneous, and the developed maps can help guide intervention, monitoring and surveillance strategies as countries progress towards LF elimination.

The impact of residual infections on Anopheles-transmitted Wuchereria bancrofti after multiple rounds of mass drug administration

BACKGROUND

Many countries have made significant progress in the implementation of World Health Organization recommended preventive chemotherapy strategy, to eliminate lymphatic filariasis (LF). However, pertinent challenges such as the existence of areas of residual infections in disease endemic districts pose potential threats to the achievements made. Thus, this study was undertaken to assess the importance of these areas in implementation units (districts) where microfilaria (MF) positive individuals could not be found during the mid-term assessment after three rounds of mass drug administration.

METHODS

This study was undertaken in Bo and Pujehun, two LF endemic districts of Sierra Leone, with baseline MF prevalence of 2 % and 0 % respectively in sentinel sites for monitoring impact of the national programme. Study communities in the districts were purposefully selected and an assessment of LF infection prevalence was conducted together with entomological investigations undertaken to determine the existence of areas with residual MF that could enable transmission by local vectors. The transmission Assessment Survey (TAS) protocol described by WHO was applied in the two districts to determine infection of LF in 6-7 year old children who were born before MDA against LF started.

RESULTS

The results indicated the presence of MF infected children in Pujehun district. An. gambiae collected in the district were also positive for W. bancrofti, even though the prevalence of infection was below the threshold associated with active transmission.

CONCLUSIONS

Residual infection was detected after three rounds of MDA in Pujehun--a district of 0 % Mf prevalence at the sentinel site. Nevertheless, our results showed that the transmission was contained in a small area. With the scale up of vector control in Anopheles transmission zones, some areas of residual infection may not pose a serious threat for the resurgence of LF if the prevalence of infections observed during TAS are below the threshold required for active transmission of the parasite. However, robust surveillance strategies capable of detecting residual infections must be implemented, together with entomological assessments to determine if ongoing vector control activities, biting rates and infection rates of the vectors can support the transmission of the disease. Furthermore, in areas where mid-term assessments reveal MF prevalence below 1 % or 2 % antigen level, in Anopheles transmission areas with active and effective malaria vector control efforts, the minimum 5 rounds of MDA may not be required before implementing TAS. Thus, we propose a modification of the WHO recommendation for the timing of sentinel and spot-check site assessments in national programs.

Lymphatic filariasis among children and adolescents: spatial identification via socio-environmental indicators to define priority areas for elimination

BACKGROUND

The occurrence of lymphatic filariasis (LF) and its transmission dynamics among children and adolescents are still not clearly elucidated. The aim of this study was to describe the spatial distribution of microfilaremia and its relationship with socio-environmental variables, thereby identifying areas at greater risk of transmission.

METHODS

An ecological study was conducted, in which the analysis unit was formed by districts of the municipality of Jaboatão dos Guararapes in the state of Pernambuco, Brazil. The data source was a parasitological survey. Inadequate sewage disposal, number of people in the household and income of between 0.5 and 1 minimum salary were used to construct the socio-environmental indicator. The districts were then grouped according to the indicator into three risk strata, using the k-means clustering technique.

RESULTS

In the study, 96/8670 (1.1%) of the population were found to present microfilaremia. The high-risk stratum had a mean prevalence rate of 1.9% and a risk of 2.56 (p<0.05), in relation to the low-risk stratum. The middle stratum grouped the households that presented an intermediate risk of transmission, with a prevalence rate of 1.92%.

CONCLUSIONS

The indicator used is a promising tool that enables the precise measurement of the relationship between social deprivation and the prevalence of filarial infection among children. Thus, it can be used to plan control and elimination actions.

A comparison of two tests for filarial antigenemia in areas in Sri Lanka and Indonesia with low-level persistence of lymphatic filariasis following mass drug administration

BACKGROUND

Filarial antigen tests are key tools for mapping the distribution of bancroftian filariasis and for detecting areas with persistent infections following mass drug administration (MDA). A recent study showed that the new Alere Filariasis Test Strip (FTS) has better analytical sensitivity than the BinaxNOW Filariasis card test (Card Test) for detecting circulating filarial antigen, and the FTS detected more positive results than the Card Test in a field study performed in a highly endemic area in Liberia.

METHODS

The present study compared the performance of the FTS and the Card Test in community surveys that were conducted in southern Sri Lanka and in Indonesia (Central Java) in areas with low-level persistence of LF following multiple rounds of MDA with diethylcarbamazine plus albendazole. The studies were performed in densely populated semi-urban areas where Wuchereria bancrofti is transmitted by Culex quinquefasciatus.

RESULTS

Antigenemia rates by FTS were 138% higher in the Sri Lanka study (43/852 vs. 18/852) and 21% higher in the Indonesia study (50/778 vs. 41/778) than antigenemia rates by Card Test. Antigenemia rates were significantly higher in males than in females and higher in adults than in children in both study sites. Although overall antigenemia rates and test scores were significantly higher by FTS than by Card Test in both study areas, rates in young children were similar with both tests in both areas.

CONCLUSIONS

These results extend the previously reported superior sensitivity of the FTS to areas with low residual infection rates following MDA, and this could affect mapping and post-MDA survey results in adults. However, our findings suggest that results of transmission assessment surveys (TAS) performed in school-aged children are likely to be similar with both tests.