Subnational Projections of Lymphatic Filariasis Elimination Targets in Ethiopia to Support National Level Policy

BACKGROUND

Lymphatic filariasis (LF) is a debilitating, poverty-promoting, neglected tropical disease (NTD) targeted for worldwide elimination as a public health problem (EPHP) by 2030. Evaluating progress towards this target for national programmes is challenging, due to differences in disease transmission and interventions at the subnational level. Mathematical models can help address these challenges by capturing spatial heterogeneities and evaluating progress towards LF elimination and how different interventions could be leveraged to achieve elimination by 2030.

METHODS

Here we used a novel approach to combine historical geo-spatial disease prevalence maps of LF in Ethiopia with 3 contemporary disease transmission models to project trends in infection under different intervention scenarios at subnational level.

RESULTS

Our findings show that local context, particularly the coverage of interventions, is an important determinant for the success of control and elimination programmes. Furthermore, although current strategies seem sufficient to achieve LF elimination by 2030, some areas may benefit from the implementation of alternative strategies, such as using enhanced coverage or increased frequency, to accelerate progress towards the 2030 targets.

CONCLUSIONS

The combination of geospatial disease prevalence maps of LF with transmission models and intervention histories enables the projection of trends in infection at the subnational level under different control scenarios in Ethiopia. This approach, which adapts transmission models to local settings, may be useful to inform the design of optimal interventions at the subnational level in other LF endemic regions.

How Does the Proportion of Never Treatment Influence the Success of Mass Drug Administration Programs for the Elimination of Lymphatic Filariasis?

BACKGROUND

Mass drug administration (MDA) is the cornerstone for the elimination of lymphatic filariasis (LF). The proportion of the population that is never treated (NT) is a crucial determinant of whether this goal is achieved within reasonable time frames.

METHODS

Using 2 individual-based stochastic LF transmission models, we assess the maximum permissible level of NT for which the 1% microfilaremia (mf) prevalence threshold can be achieved (with 90% probability) within 10 years under different scenarios of annual MDA coverage, drug combination and transmission setting.

RESULTS

For Anopheles-transmission settings, we find that treating 80% of the eligible population annually with ivermectin + albendazole (IA) can achieve the 1% mf prevalence threshold within 10 years of annual treatment when baseline mf prevalence is 10%, as long as NT <10%. Higher proportions of NT are acceptable when more efficacious treatment regimens are used. For Culex-transmission settings with a low (5%) baseline mf prevalence and diethylcarbamazine + albendazole (DA) or ivermectin + diethylcarbamazine + albendazole (IDA) treatment, elimination can be reached if treatment coverage among eligibles is 80% or higher. For 10% baseline mf prevalence, the target can be achieved when the annual coverage is 80% and NT ≤15%. Higher infection prevalence or levels of NT would make achieving the target more difficult.

CONCLUSIONS

The proportion of people never treated in MDA programmes for LF can strongly influence the achievement of elimination and the impact of NT is greater in high transmission areas. This study provides a starting point for further development of criteria for the evaluation of NT.

Impact of conflict on the elimination targets of lymphatic filariasis, schistosomiasis and soil-transmitted helminths in Cabo Delgado province, Mozambique

BACKGROUND

Mozambique has one of the highest burdens of neglected tropical diseases in Africa. Lymphatic filariasis, schistosomiasis and soil-transmitted helminths are being targeted for elimination as part of integrated mass drug administration campaigns. The progress made towards interruption of transmission has been affected by recent conflict in Cabo Delgado province. The aim of this paper was to determine the potential impact of this crisis on the neglected tropical diseases programme and the challenges in reaching the elimination goals of 2030.

METHODOLOGY

A desk-based secondary data analysis was conducted on publicly available sources of neglected tropical diseases, conflict incidents, internally displaced persons and geographical access between 2020 and 2022. Data were summarised and mapped using GIS software. A combined risk stratified assessment at district level was developed with five classifications i) Very high-risk; ii) High-risk; iii) Medium to high-risk; iv) Medium risk; and v) Not at risk due to conflict absence but co-endemic.

RESULTS

Lymphatic filariasis, schistosomiasis and soil-transmitted helminths were co-endemic in 115 out of 156 (74%) districts. Between 2020 and 2022 a total of 1,653 conflict-related incidents were reported, most of them in Cabo Delgado province (n = 1,397, 85%). A five-fold increase of internally displaced persons was recorded from April 2020 (n = 172,186) to November 2022 (n = 935,130). Geographical accessibility also deteriorated across the province with an increase from five (29%) in 2021 to seven (41%) districts in 2022 classified as hard-to-reach. The combined risk stratification identified that most districts in Cabo Delgado province had medium to high-risk (n = 7; 41%); very high-risk (n = 5, 29%); medium risk (n = 3, 18%); high-risk (n = 2, 12%).

CONCLUSION

Most of the districts of Cabo Delgado were considered to be at risk of not meeting the neglected tropical diseases road map 2030 targets due to the humanitarian crisis ongoing. There is the need for practical strategies and funding to overcome these hostile challenges.

Entomological assessment in 'hotspots' of four lymphatic filariasis endemic districts, Central Nepal during post-MDA surveillance

BACKGROUND OBJECTIVES

Annual mass drug administration (MDA) is the main strategy to interrupt the transmission of lymphatic filariasis (LF) in the community. The main aim of monitoring the MDA program, for its effectiveness and interruption of LF is the post-MDA surveillance using antigen survey in children born after MDA. The latest technique of new research suggests that xenomonitoring is an effective tool for monitoring LF intervention. The objective of this study was to assess the W. bancrofti infection/or infectivity in vector mosquitoes by xenomonitoring during post-MDA surveillance.

METHODS

A descriptive cross-sectional study was conducted in the hotspots of selected four districts of Central Nepal. A gravid trap technique was used for sampling mosquitoes. Infection/or infectivity was determined via the dissection of vector mosquitoes. Anopheles, Aedes, Armigerus and Culex species were collected from hotspots of four endemic districts, two from the hilly region (Lalitpur and Dhading) and two from Terai region (Bara and Mahottari) of Central Nepal.

RESULTS

A total of 4450 mosquitoes belonging to four genera, Anopheles, Culex, Armigeres, and Aedes were collected from four hotspots. The distribution of Culex quinquefasciatus was found to be the highest, 88.9% (n=3955/4450) followed by Cx. vishnui (4.5%), Armigeres sp (5.8%), An. culicifascies (0.2%), Aedes spp (0.8%). The proportion of female mosquitoes trapped is significantly higher. A total of 3344 parous Cx. quinquefasciatus mosquitoes were dissected for any larval stage of W. bancrofti. We could not find any filarial infection in dissected mosquito samples.

INTERPRETATION CONCLUSION

We conclude that the gravid trap is an efficient tool for the collection of gravid Cx. quinquefasciatus mosquitoes for xenomonitoring studies of filariasis endemic regions. Vector composition indicated a maximum number of vector mosquitoes of lymphatic filariasis were trapped compared with the other three species. Distribution and density of Cx. quinquefasciatus was found highest in four hotspots of endemic districts. None of the Cx. quinquefasciatus dissected were found to be infected by larval forms of filaria. Since the low levels of infection persistence in the human population in these hot spots, vector infection and infectivity can't be ignored. Microscopic xenomonitoring at a low level of infection persistent is less likely to be efficient so molecular xenomonitoring along with a large sample should be required in each of the hot spots of the districts. Additionally, area is receptive so further vector control intervention should be required to reduce the risk of resurgence of infection.

Lymphatic filariasis elimination status: Wuchereria bancrofti infections in human populations and factors contributing to continued transmission after seven rounds of mass drug administration in Masasi District, Tanzania

BACKGROUND

Lymphatic filariasis (LF) affects more than 120 million people globally. In Tanzania, nearly six million people are estimated to live with clinical manifestations of the disease. The National LF control program was established in 2000 using Mass drug administration (MDA) of Ivermectin and Albendazole to individuals aged 5years and above. This study assessed the infection status in individuals aged 15 years and above who are eligible for participation in MDA. The level of compliance to MDA and the reasons for non-compliance to MDA were also assessed.

METHODS

A community based cross-sectional study was conducted in two villages of Masasi District. A total of 590 participants aged 15 years and above were screened for the circulating filarial antigen (CFA) using the rapid diagnostic test. Night blood samples from CFA positive individuals were further analyzed for detection and quantification of Wuchereria bancrofti microfilaria (Mf) using the counting chamber technique. A pre-tested questionnaire was administered to collect information on compliance to MDA and the factors affecting continued transmission. Data were analyzed using SPSS Version 20. Chi-square test was used to compare the prevalence of CFA by gender and village where a P-value ≤0.05 was considered statistically significant.

RESULTS

Out of 590 participants, 30 (5.1%) were positive for CFA and one (0.2%) was found positive for microfilaria of Wuchereria bancrofti. Compliance during the last round of MDA, in the year 2019 was 56% which is below the minimum coverage recommended by WHO. Absence from home during MDA and perceptions of being free from hydrocele or elephantiasis were the major reasons for non-compliance.

CONCLUSION

There is a significant decline in LF transmission in Masasi District after seven rounds of MDA. However, the presence of individuals who are persistently non-compliant may delay elimination of LF in the District.

Simulating the effect of evaluation unit size on eligibility to stop mass drug administration for lymphatic filariasis in Haiti

Background

The Transmission Assessment Survey (TAS) is a decision-making tool to determine when transmission of lymphatic filariasis is presumed to have reached a level low enough that it cannot be sustained even in the absence of mass drug administration. The survey is applied over geographic areas, called evaluation units (EUs); existing World Health Organization guidelines limit EU size to a population of no more than 2 million people.

Methodology/Principal findings

In 2015, TASs were conducted in 14 small EUs in Haiti. Simulations, using the observed TAS results, were performed to understand the potential programmatic impact had Haiti chosen to form larger EUs. Nine “combination-EUs” were formed by grouping adjacent EUs, and bootstrapping was used to simulate the expected TAS results.

When the combination-EUs were comprised of at least one “passing” and one “failing” EU, the majority of these combination-EU would pass the TAS 79% - 100% of the time. Even in the case when both component EUs had failed, the combination-EU was expected to “pass” 11% of the time.

Simulations of mini-TAS, a strategy with smaller power and hence smaller sample size than TAS, resulted in more conservative “passing” and “failing” when implemented in original EUs.

Conclusions/Significance

Our results demonstrate the high potential for misclassification when the average prevalence of lymphatic filariasis in the combined areas differs with regards to the TAS threshold. Of particular concern is the risk of “passing” larger EUs that include focal areas where prevalence is high enough to be potentially self-sustaining. Our results reaffirm the approach that Haiti took in forming smaller EUs. Where baseline or monitoring data show a high or heterogeneous prevalence, programs should leverage alternative strategies like mini-TAS in smaller EUs, or consider gathering additional data through spot check sites to advise EU formation.

Lymphatic filariasis is a disease caused by roundworms that may lead to disability, psychological problems, stigma, and lowered quality of life. One of the key strategies to control and eliminate lymphatic filariasis is mass drug administration (MDA), or repeated treatment of all at-risk people living in affected areas with an annual dose of medicine. To determine whether MDA can be stopped in a particular area, a transmission assessment survey (TAS) is conducted whereby a sample of children are tested for filarial antigen and proportion with a positive result is compared against a target threshold. Existing guidelines for delimiting the geographic areas to conduct TAS permit large evaluation units. In 2015, TASs were conducted in Haiti using more stringent criteria for forming evaluation units, resulting in much smaller geographic areas for evaluation. Using simulations, the authors found that, had Haiti followed the existing guidelines and assessed larger geographic areas, many of the areas might have been misclassified and MDA stopped prematurely in some settings. This research suggests that caution is needed when forming evaluation units for TAS, especially if the prevalence of lymphatic filariasis is not uniform.

Strengthening data collection for neglected tropical diseases: What data are needed for models to better inform tailored intervention programmes?

Locally tailored interventions for neglected tropical diseases (NTDs) are becoming increasingly important for ensuring that the World Health Organization (WHO) goals for control and elimination are reached. Mathematical models, such as those developed by the NTD Modelling Consortium, are able to offer recommendations on interventions but remain constrained by the data currently available. Data collection for NTDs needs to be strengthened as better data are required to indirectly inform transmission in an area. Addressing specific data needs will improve our modelling recommendations, enabling more accurate tailoring of interventions and assessment of their progress. In this collection, we discuss the data needs for several NTDs, specifically gambiense human African trypanosomiasis, lymphatic filariasis, onchocerciasis, schistosomiasis, soil-transmitted helminths (STH), trachoma, and visceral leishmaniasis. Similarities in the data needs for these NTDs highlight the potential for integration across these diseases and where possible, a wider spectrum of diseases.

Supporting elimination of lymphatic filariasis in Samoa by predicting locations of residual infection using machine learning and geostatistics

The global elimination of lymphatic filariasis (LF) is a major focus of the World Health Organization. One key challenge is locating residual infections that can perpetuate the transmission cycle. We show how a targeted sampling strategy using predictions from a geospatial model, combining random forests and geostatistics, can improve the sampling efficiency for identifying locations with high infection prevalence. Predictions were made based on the household locations of infected persons identified from previous surveys, and environmental variables relevant to mosquito density. Results show that targeting sampling using model predictions would have allowed 52% of infections to be identified by sampling just 17.7% of households. The odds ratio for identifying an infected individual in a household at a predicted high risk compared to a predicted low risk location was 10.2 (95% CI 4.2-22.8). This study provides evidence that a 'one size fits all' approach is unlikely to yield optimal results when making programmatic decisions based on model predictions. Instead, model assumptions and definitions should be tailored to each situation based on the objective of the surveillance program. When predictions are used in the context of the program objectives, they can result in a dramatic improvement in the efficiency of locating infected individuals.

Defining a prevalence level to describe the elimination of Lymphatic Filariasis (LF) transmission and designing monitoring & evaluating (M&E) programmes post the cessation of mass drug administration (MDA)

The global decline in prevalence of lymphatic filariasis has been one of the major successes of the WHO's NTD programme. The recommended strategy of intensive, community-wide mass drug administration, aims to break localised transmission by either reducing the prevalence of microfilaria positive infections to below 1%, or antigen positive infections to below 2%. After the threshold is reached, and mass drug administration is stopped, geographically defined evaluation units must pass Transmission Assessment Surveys to demonstrate that transmission has been interrupted. In this study, we use an empirically parameterised stochastic transmission model to investigate the appropriateness of 1% microfilaria-positive prevalence as a stopping threshold, and statistically evaluate how well various monitoring prevalence-thresholds predict elimination or disease resurgence in the future by calculating their predictive value. Our results support the 1% filaremia prevalence target as appropriate stopping criteria. However, because at low prevalence-levels random events dominate the transmission dynamics, we find single prevalence measurements have poor predictive power for predicting resurgence, which suggests alternative criteria for restarting MDA may be beneficial.

Low transmission of Wuchereria bancrofti in cross-border districts of Côte d'Ivoire: A great step towards lymphatic filariasis elimination in West Africa

BACKGROUND

Lymphatic filariasis (LF) is widely endemic in Côte d'Ivoire, and elimination as public health problem (EPHP) is based on annual mass drug administration (MDA) using ivermectin and albendazole. To guide EPHP efforts, we evaluated Wuchereria bancrofti infection indices among humans, and mosquito vectors after four rounds of MDA in four cross-border health districts of Côte d'Ivoire.

METHODOLOGY

We monitored people and mosquitoes for W. bancrofti infections in the cross-border health districts of Aboisso, Bloléquin, Odienné and Ouangolodougou, Côte d'Ivoire. W. bancrofti circulating filarial antigen (CFA) was identified using filariasis test strips, and antigen-positive individuals were screened for microfilaremia. Moreover, filarial mosquito vectors were sampled using window exit traps and pyrethrum sprays, and identified morphologically at species level. Anopheles gambiae s.l. and Culex quinquefasciatus females were analyzed for W. bancrofti infection using polymerase chain reaction (PCR) technique.

PRINCIPAL FINDINGS

Overall, we found a substantial decline in W. bancrofti infection indices after four rounds of MDA compared to pre-MDA baseline data. CFA prevalence fell from 3.38-5.50% during pre-MDA to 0.00-1.53% after MDA interventions. No subjects had detectable levels of CFA in Ouangolodougou. Moreover, post-MDA CFA prevalence was very low, and below the 1% elimination threshold in Aboisso (0.19%) and Odienné (0.49%). Conversely, CFA prevalence remained above 1% in Bloléquin (1.53%). W. bancrofti microfilariae (Mf) were not found in Aboisso, Bloléquin, and Ouangolodougou, except for Odienné with low prevalence (0.16%; n = 613) and microfilaremia of 32.0 Mf/mL. No An. gambiae s.l. and Cx. quinquefasciatus pools were infected with W. bancrofti in Bloléquin and Ouangolodougou, while they exhibited low infection rates in Aboisso (1% and 0.07%), and Odienné (0.08% and 0.08%), respectively.

CONCLUSIONS

In cross-border areas of Côte d'Ivoire, LF infection indices in humans and mosquito vectors substantially declined after four rounds of MDA. CFA prevalence fell under the World Health Organization (WHO)-established threshold (1%) in Aboisso, Ouangolodougou and Odienné. Moreover, W. bancrofti prevalence in mosquitoes was lower than WHO-established threshold (2%) in all areas. This might suggest the interruption of W. bancrofti transmission, and possible MDA cessation. However, a formal transmission assessment survey (TAS) and molecular xenomonitoring in mosquito vectors should be implemented before eventual MDA cessation. However, MDA should pursue in Bloléquin where W. bancrofti infection prevalence remained above 1%. Our results provided important ramifications for LF control efforts towards EPHP in Côte d'Ivoire.

Assessment of transmission in areas of uncertain endemicity for lymphatic filariasis in Brazil

BACKGROUND

The objective of the Global Program to Eliminate Lymphatic Filariasis (GPELF) is to phase out this endemic disease as a public health problem by 2020. Validation of elimination is obtained from the World Health Organization through evidence of non-transmission in countries that have already been subjected to mass drug administration (MDA) and in places adjoining these endemic areas. While three municipalities in Brazil have completed MDA, the epidemiological situation remains uncertain in nine adjoining municipalities. To determine the epidemiological status, this study was to perform a review of the literature and a school-based survey to describe the past and recent endemicity of lymphatic filariasis (LF) theses nine municipalities in Brazil.

METHODOLOGY/PRINCIPLE FINDINGS

For review of the literature, both formal and informal literature sources were accessed since the first reports of filariasis in the Metropolitan Region of Recife, Brazil. We conducted a school-based survey in 2016 using immunochromatographic card tests (ICTs) among schoolchildren aged 6-10 years living in nine municipalities contiguous with the endemic areas in which MDA was conducted. Our review of the literature identified eight studies involving surveys demonstrating that microfilariae had been circulating in eight of the municipalities since 1967, with a low prevalence of microfilaremia, isolated autochthonous cases, and treatment of individual cases. The school-based survey included 17,222 children in 185 urban schools in the nine areas of Brazil with uncertain endemicity. One child affected by allochthonous transmission was antigen positive based on ICT and lived in a municipality adjacent to Recife; this child's family came from Recife, but no other case was diagnosed within the family.

CONCLUSIONS/SIGNIFICANCE

The study results suggest that there is no transmission of LF in the municipalities investigated. However, these areas have population migration and socioenvironmental conditions favorable to mosquito breeding grounds; therefore, surveillance is strongly recommended in these areas.

Elimination of lymphatic filariasis as a public health problem from the Arab Republic of Egypt

Lymphatic filariasis (LF) has been known in Egypt since ancient times. By 1930s it was recognized to be a major public health problem in the Nile Delta, and to be caused by Wuchereria bancrofti and transmitted by Culex pipiens. Remarkably, as a result of widespread DEC treatment and intensive vector control by the Ministry of Health and Population (MoHP), the infection rate of LF declined in the 1960s. However, relaxation of these efforts resulted in resurgence of filariasis in the 1980s and 1990s. In 2000, Egypt was among the first countries to join the WHO global efforts to eliminate LF as a public health problem by initiating a national LF elimination programme (NLFEP). This article reviews the history of LF control activities and summarizes the NLFEP extensive interventions to eliminate LF in Egypt. Based on MoHP data, mass drug administration (MDA) with DEC and ALB was started in 2000 in 161 implementation units (IUs). Additional IUs were included in subsequent MDA rounds, with the last IU included in 2007. MDA stopping surveys were conducted based on WHO guidelines (2005; 2011). Information about the presence of those suffering from lymphoedema/elephantiasis and hydrocele patients was collected, and care provided to those needing care in five rural health units (RHU) by primary health care system providers who were given training on LF morbidity management and disability prevention (MMDP). The NLFEP made excellent progress due to strong collaboration between different ministries, through intensive training and supervision, and the use of advocacy for mobilization of endemic communities. The epidemiological coverage for all MDA rounds was effectively ≥80%. Antigenemia levels found in schoolchildren during transmission assessment surveys (TAS) in 166 IUs approximately 10 years after stopping MDA was 0%. In 2017, TAS conducted in additional 29 IUs indicated 0.1% antigenemia and 0% microfilaremia. In 2015, the registration of chronic LF patients was updated to 1472 lymphoedema and 18 hydrocele patients. Lymphoedema patients were trained on self-management, and hydrocele patients were referred to local General Hospitals for surgery. Thus, after over a decade of sustained effort, Egypt met the WHO criteria for successful elimination of LF as a public health problem. In December 2017, WHO validated Egypt as the first country in the Eastern Mediterranean Region to successfully achieve elimination.

Potential of hydrocarbon and oxygenated monoterpenes against Culex pipiens larvae: Toxicity, biochemical, pharmacophore modeling and molecular docking studies

Culex pipiens is a main vector for Bancroftian filariasis, Rift Valley Fever and diseases caused by other viruses, leaving several peoples with disabilities. In recent years, plant derived compounds have received much attention as potential alternatives to synthetic chemicals due to their low toxicity to mammals and environmental persistence. Twenty-one monoterpenes from different chemical groups (hydrocarbons and oxygenated products) were evaluated against Culex pipiens larvae. In addition, in vivo biochemical studies including effects on acetylcholine esterase (AChE), acid and alkaline phosphatases (ACP and ALP), total adenosine triphosphatase (ATPase) and gamma-aminobutyric acid transaminase (GABA-T) were investigated. Furthermore, in silico studies including pharmacophore elucidation, ADMET analysis and molecular docking of these compounds were performed. Among all tested monoterpenes, hydrocarbons [p-cymene, (R)-(+)-limonene and (+)-α-pinene], acetates (cinnamyl acetate, citronellyl acetate, eugenyl acetate and terpinyl acetate), alcohols [(±)-β-citronellol and terpineol], aldehydes [citral and (1R)-(-)-myrtenal] and ketone [(R)-(+)-pulegone] exhibited the highest larval toxicity with LC₅₀ = 14.88, 27.97, 26.13, 2.62, 3.81, 2.74, 21.65, 1.64, 21.70, 21.76, 1.68 and 1.90 mg/L after 48 h of exposure, respectively. The compounds proved a significant inhibition of all tested enzymes except total ATPase. The biochemical and molecular docking studies proved that AChE and GABA-T were the main targets for the tested monoterpenes.

Insecticide resistance mapping in the vector of lymphatic filariasis, Culex quinquefasciatus Say from northern region of West Bengal, India

Culex quinquefasciatus is a vector of lymphatic filariasis and vector control strategies normally involve the use of synthetic insecticides targeted against them. Extensive and uncontrolled use of these synthetic insecticides has led to the development of insecticide resistance in the mosquito vectors. In this context, to study the resistance status of Cx. quinquefasciatus, field populations were collected from three districts of Northern part of West Bengal and tested against insecticides (5% malathion, 0.05% deltamethrin, 0.05% lambdacyhalothrin,0.75% permethrin, 0.1% propoxur, 4% DDT and Temephos). Qualitative and quantitative enzyme assay was also conducted in order to find the role of detoxifying enzymes behind the development of insecticide resistance. This study revealed the presence of widespread resistance amongst the field populations of Cx. quinquefasciatus throughout the studied regions. Moreover, the result of native PAGE and biochemical enzyme assay may be linked to some extent in the involvement of the detoxifying enzymes in conferring resistance against insecticides in most of the tested Cx. quinquefasciatus populations. The present study involving the survey of resistance status may be of immense help during the implementation of vector control strategies throughout this region.

Lymphatic Filariasis

Lymphatic filariasis (LF) is a parasitic infection that is spread by mosquitos infected with worm larvae. Several factors will affect the global prevalence of LF in the future. A growing body of evidence suggests that climate change will influence the spread of parasitic diseases and their vectors. Lymphatic filariasis is the leading cause of permanent disfigurement and the second most common cause of long-term disability in the world.

Elimination within reach: A cross-sectional study highlighting the factors that contribute to persistent lymphatic filariasis in eight communities in rural Ghana

Background

Despite the progress achieved in scaling-up mass drug administration (MDA) for lymphatic filariasis (LF) in Ghana, communities with persistent LF still exist even after 10 years of community treatment. To understand the reasons for persistence, we conducted a study to assess the status of disease elimination and understand the adherence to interventions including MDA and insecticide treated nets.

Methodology and principal findings

We conducted a parasitological and epidemiological cross-sectional study in adults from eight villages still under MDA in the Northern Region savannah and the coastal Western Region of the country. Prevalence of filarial antigen ranged 0 to 32.4% and in five villages the prevalence of night blood microfilaria (mf) was above 1%, ranging from 0 to 5.7%. Median mf density was 67 mf/ml (range: 10–3,560). LF antigen positivity was positively associated with male sex but negatively associated with participating in MDA the previous year. Male sex was also associated with a decreased probability of participating in MDA. A stochastic model (TRANSFIL) was used to assess the expected microfilaria prevalence under different MDA coverage scenarios using historical data on one community in the Western Region. In this example, the model simulations suggested that the slow decline in mf prevalence is what we would expect given high baseline prevalence and a high correlation between MDA adherence from year to year, despite high MDA coverage.

Conclusions

There is a need for an integrated quantitative and qualitative research approach to identify the variations in prevalence, associated risk factors and intervention coverage and use levels between and within regions and districts. Such knowledge will help target resources and enhance surveillance to the communities most at risk and to reach the 2020 LF elimination goals in Ghana.

Lymphatic filariasis (LF) is a mosquito-borne disease and a leading cause of disability and chronic morbidity worldwide. Despite the progress achieved so far in stopping LF transmission by treating the affected communities with specific drugs over several years, areas where lymphatic filariasis persists still exist. Understanding the reasons behind this is pivotal to both reach and sustain elimination. We investigated the factors associated with filariasis persistence in various communities still under drug treatment from two regions of Ghana. We reported high variability in disease burden, adherence to drug treatment and mosquito net use between regions and communities. LF infection was associated with men and not taking the drugs, and men were also less likely to take treatment. Using mathematical modelling, we showed that slight increases in treatment coverage will accelerate elimination. Our findings highlight the reasons for LF persistence and provide guidance on how to successfully achieve elimination by refining drug treatment distribution and mosquito control interventions more tailored to individuals and communities. We also demonstrated the value of using field-collected data in mathematical models to assess the current status of disease elimination and to identify the gaps in control interventions.

Flubendazole as a macrofilaricide: History and background

Benzimidazole anthelmintics have long been employed for the control of soil-transmitted helminth infections. Flubendazole (FBZ) was approved in 1980 for the treatment of gastrointestinal nematode infections in both veterinary and human medicine. It has also long been known that parenteral administration of FBZ can lead to high macrofilaricidal efficacy in a variety of preclinical models and in humans. As part of an effort to stimulate the discovery and development of new macrofilaricides, particularly for onchocerciasis, research has recently been devoted to the development of new formulations that would afford high oral bioavailability of FBZ, paving the way for potential clinical development of this repurposed drug for the treatment of human filariases. This review summarizes the background information that led to this program and summarizes some of the lessons learned from it.

Kernel-density estimation and approximate Bayesian computation for flexible epidemiological model fitting in Python

Fitting complex models to epidemiological data is a challenging problem: methodologies can be inaccessible to all but specialists, there may be challenges in adequately describing uncertainty in model fitting, the complex models may take a long time to run, and it can be difficult to fully capture the heterogeneity in the data. We develop an adaptive approximate Bayesian computation scheme to fit a variety of epidemiologically relevant data with minimal hyper-parameter tuning by using an adaptive tolerance scheme. We implement a novel kernel density estimation scheme to capture both dispersed and multi-dimensional data, and directly compare this technique to standard Bayesian approaches. We then apply the procedure to a complex individual-based simulation of lymphatic filariasis, a human parasitic disease. The procedure and examples are released alongside this article as an open access library, with examples to aid researchers to rapidly fit models to data. This demonstrates that an adaptive ABC scheme with a general summary and distance metric is capable of performing model fitting for a variety of epidemiological data. It also does not require significant theoretical background to use and can be made accessible to the diverse epidemiological research community.

An assessment of mosquito collection techniques for xenomonitoring of anopheline-transmitted Lymphatic Filariasis in Ghana

Monitoring vectors is relevant to ascertain transmission of lymphatic filariasis (LF). This may require the best sampling method that can capture high numbers of specific species to give indication of transmission. Gravid anophelines are good indicators for assessing transmission due to close contact with humans through blood meals. This study compared the efficiency of an Anopheles gravid trap (AGT) with other mosquito collection methods including the box and the Centres for Disease Control and Prevention gravid, light, exit and BioGent-sentinel traps, indoor resting collection (IRC) and pyrethrum spray catches across two endemic regions of Ghana. The AGT showed high trapping efficiency by collecting the highest mean number of anophelines per night in the Western (4.6) and Northern (7.3) regions compared with the outdoor collection methods. Additionally, IRC was similarly efficient in the Northern region (8.9) where vectors exhibit a high degree of endophily. AGT also showed good trapping potential for collecting Anopheles melas which is usually difficult to catch with existing methods. Screening of mosquitoes for infection showed a 0.80-3.01% Wuchereria bancrofti and 2.15-3.27% Plasmodium spp. in Anopheles gambiae. The AGT has shown to be appropriate for surveying Anopheles populations and can be useful for xenomonitoring for both LF and malaria.

The prevalence of lymphatic filariasis infection and disease following six rounds of mass drug administration in Mandalay Region, Myanmar

Lymphatic filariasis is widely endemic in Myanmar. Despite the establishment of an elimination program in 2000, knowledge of the remaining burden of disease relies predominantly on programmatic information. To assist the program, we conducted an independent cross-sectional household cluster survey to determine the prevalence of filariasis infection, morbidity and mass-drug administration coverage in four townships of the Mandalay Region: Amarapura, Patheingyi, Tada-U and Wundwin. The survey included 1014 individuals from 430 randomly selected households in 24 villages. Household members one year and older were assessed for antigenaemia using immunochromatographic test cards and if positive, microfilaraemia by night-time thick blood smear. Participants 15 years and older were assessed for filariasis morbidity by ultrasound-assisted clinical examination. The overall prevalence of infection was 2.63% by antigenaemia (95% confidence interval (CI) 1.71-4.04%) and 1.03% by microfilaraemia (95%CI 0.59-1.47%). The prevalence of hydrocoele in adult males was 2.78% (95%CI 1.23-6.15%) and of lymphoedema in both genders was 0% (95%CI 0-0.45%). These results indicate the persistence of filarial infection and transmission despite six rounds of annual mass drug administration and highlight the need for further rounds as well as the implementation of morbidity management programs in the country.

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.

Identifying residual transmission of lymphatic filariasis after mass drug administration: Comparing school-based versus community-based surveillance - American Samoa, 2016

INTRODUCTION

Under the Global Programme to Eliminate Lymphatic Filariasis (LF), American Samoa conducted seven rounds of mass drug administration (MDA) from 2000-2006. The World Health Organization recommends systematic post-MDA surveillance using Transmission Assessment Surveys (TAS) for epidemiological assessment of recent LF transmission. We compared the effectiveness of two survey designs for post-MDA surveillance: a school-based survey of children aged 6-7 years, and a community-based survey targeting people aged ≥8 years.

METHODS

In 2016, we conducted a systematic school-based TAS in all elementary schools (N = 29) and a cluster survey in 28 villages on the two main islands of American Samoa. We collected information on demographics and risk factors for infection using electronic questionnaires, and recorded geo-locations of schools and households. Blood samples were collected to test for circulating filarial antigen (CFA) using the Alere Filariasis Test Strip. For those who tested positive, we prepared slides for microscopic examination of microfilaria and provided treatment. Descriptive statistics were performed for questionnaire variables. Data were weighted and adjusted to account for sampling design and sex for both surveys, and for age in the community survey.

RESULTS

The school-based TAS (n = 1143) identified nine antigen-positive children and found an overall adjusted CFA prevalence of 0.7% (95% CI: 0.3-1.8). Of the nine positive children, we identified one microfilariaemic 7-year-old child. The community-based survey (n = 2507, 711 households) identified 102 antigen-positive people, and estimated an overall adjusted CFA prevalence of 6.2% (95% CI: 4.5-8.6). Adjusted village-level prevalence ranged from 0-47.1%. CFA prevalence increased with age and was higher in males. Of 86 antigen-positive community members from whom slides were prepared, 22 (25.6%) were microfilaraemic. School-based TAS had limited sensitivity (range 0-23.8%) and negative predictive value (range 25-83.3%) but had high specificity (range 83.3-100%) and positive predictive value (range 0-100%) for identifying villages with ongoing transmission.

CONCLUSIONS

American Samoa failed the school-based TAS in 2016, and the community-based survey identified higher than expected numbers of antigen-positive people. School-based TAS was logistically simpler and enabled sampling of a larger proportion of the target population, but the results did not provide a good indication of the overall CFA prevalence in older age groups and was not sensitive at identifying foci of ongoing transmission. The community-based survey, although operationally more challenging, identified antigen-positive individuals of all ages, and foci of high antigen prevalence. Both surveys confirmed recrudescence of LF transmission.

Increasing evidence of low lymphatic filariasis prevalence in high risk Loa loa areas in Central and West Africa: a literature review

In West and Central Africa, there is a need to establish the prevalence of Wuchereria bancrofti in areas that are co-endemic for Loa loa, in order to implement the appropriate strategies to scale-up interventions for the elimination of lymphatic filariasis (LF). Due to the risk of severe adverse events (SAEs) to ivermectin in individuals with high L. loa microfilaraemia, the current strategy recommended by the World Health Organization (WHO) is twice yearly mass drug administration (MDA) with albendazole, supplemented by vector control targeting the Anopheles vectors. Defining W. bancrofti prevalence in areas co-endemic with L. loa is complicated by the cross-reactivity of rapid diagnostic immunochromatographic card tests (ICT), widely used for LF mapping, in individuals with high L. loa microfilaraemia. This has probably resulted in the overestimation of LF prevalence, triggering the implementation of MDA strategies, which may be unnecessary and wasteful of the limited resources for elimination programme implementation. Here we review the literature and present historical evidence, which uniformly highlight low or no prevalence of W. bancrofti infection and/or clinical LF cases across five Central African countries, in more than 30 different geographical areas covering 280 individual sites and > 22,000 individuals tested within high risk L. loa areas. This highlights the very limited information available on LF prevalence in L. loa areas, and potentially has major policy implications, which could shift the focus towards revised mapping criteria to verify low or no W. bancrofti prevalence in high risk L. loa areas. In this situation, revising the current WHO strategy from MDA, to focus more on ensuring high and effective vector control, through insecticide treated/long-lasting impregnated bednets (ITNs/LLINs), integration of point-of-care test-and-treat options into health systems, and consolidating closer links with the malaria control programme may be a more effective and appropriate use of the limited resources and drug donations available for LF elimination.

Insulin receptor knockdown blocks filarial parasite development and alters egg production in the southern house mosquito, Culex quinquefasciatus

Lymphatic filariasis, commonly known as elephantiasis, is a painful and profoundly disfiguring disease. Wuchreria bancrofti (Wb) is responsible for >90% of infections and the remainder are caused by Brugia spp. Mosquitoes of the genera Culex (in urban and semi-urban areas), Anopheles (in rural areas of Africa and elsewhere), and Aedes (in Pacific islands) are the major vectors of W. bancrofti. A preventive chemotherapy called mass drug administration (MDA), including albendazole with ivermectin or diethylcarbamazine citrate (DEC) is used in endemic areas. Vector control strategies such as residual insecticide spraying and long-lasting insecticidal nets are supplemental to the core strategy of MDA to enhance elimination efforts. However, increasing insecticide resistance in mosquitoes and drug resistance in parasite limit the effectiveness of existing interventions, and new measures are needed for mosquito population control and disruption of mosquito-parasite interactions to reduce transmission. Mosquito insulin signaling regulates nutrient metabolism and has been implicated in reduced prevalence and intensity of malaria parasite, Plasmodium falciparum, infection in mosquitoes. Currently no data are available to assess how insulin signaling in mosquitoes affects the development of multi-cellular parasites, such as filarial nematodes. Here, we show that insulin receptor knockdown in blood fed C. quinquefasciatus, the major vector of Wb in India, completely blocks the development of filarial nematode parasite to the infective L3 stage, and results in decreased ecdysteroid production and trypsin activity leading to fewer mosquito eggs. These data indicate that a functional mosquito insulin receptor (IR) is necessary for filarial parasite development and mosquito reproduction. Therefore, insulin signaling may represent a new target for the development of vector control or parasite blocking strategies.

Lymphatic filariasis (LF) is caused by infection with nematodes of the family Filarioidea. 90% of infections are caused by Wuchereria bancrofti and the remainder by Brugia spp. In endemic countries, LF has a major social and economic impact with an estimated annual loss of $1 billion. Filarial infection can cause a variety of clinical manifestations, including lymphoedema of the limbs, genital disease (hydrocele, and swelling of the scrotum and penis) and recurrent acute attacks, which are extremely painful and are accompanied by fever. As one of the leading causes of global disability, LF accounts for at least 2.8 million disability-adjusted life year (DALY). Mass drug administration (MDA) is used prophylactically on the community level where the infection is present to decrease disease transmission. These drugs have limited effect on adult parasites but effectively reduce microfilariae in the bloodstream and prevent the spread of microfilaria to mosquitoes. Use of mosquito population control strategies is supplemental to the core strategy of MDA. However, increasing insecticide resistance in mosquitoes and drug resistant nematode parasites are complicating elimination efforts and emphasizes the need for novel interventions for vector control and parasite transmission. Insulin signaling is a highly conserved signaling pathway that regulates growth and nutrient homeostasis in animals. Our previous work in Aedes aegypti mosquitoes showed additional roles of insulin receptor signaling in blood digestion and reproduction. The present data strongly supports our previous findings in a different mosquito species and further explores the role of mosquito insulin receptor in the development of the filarial nematode to the infective stage. This information is pertinent to ongoing efforts to control and eradicate filariasis because insulin signaling may represent a new target for the development of vector control or transmission blocking strategies.

Results of a confirmatory mapping tool for Lymphatic filariasis endemicity classification in areas where transmission was uncertain in Ethiopia

Background

The goal of the global lymphatic filariasis (LF) program is to eliminate the disease as a public health problem by the year 2020. The WHO mapping protocol that is used to identify endemic areas in need of mass drug administration (MDA) uses convenience-based sampling. This rapid mapping has allowed the global program to dramatically scale up treatment, but as the program approaches its elimination goal, it is important to ensure that all endemic areas have been identified and have received MDA. In low transmission settings, the WHO mapping protocol for LF mapping has several limitations. To correctly identify the LF endemicity of woredas, a new confirmatory mapping tool was developed to test older school children for circulating filarial antigen (CFA) in settings where it is uncertain. Ethiopia is the first country to implement this new tool. In this paper, we present the Ethiopian experience of implementing the new confirmatory mapping tool and discuss the implications of the results for the LF program in Ethiopia and globally.

Methods

Confirmatory LF mapping was conducted in 1,191 schools in 45 woredas, the implementation unit in Ethiopia, in the regions of Tigray, Amhara, Oromia, SNNP, Afar and Harari, where the results of previous mapping for LF using the current WHO protocol indicated that LF endemicity was uncertain. Within each woreda schools were selected using either cluster or systematic sampling. From selected schools, a total of 18,254 children were tested for circulating filarial antigen (CFA) using the immuno-chromatographic test (ICT).

Results

Of the 18,254 children in 45 woredas who participated in the survey, 28 (0.16%) in 9 woredas tested CFA positive. According to the confirmatory mapping threshold, which is ≥2% CFA in children 9–14 years of age, only 3 woredas out of the total 45 had more CFA positive results than the threshold and thus were confirmed to be endemic; the remaining 42 woredas were declared non-endemic. These results drastically decreased the estimated total population living in LF-endemic woredas in Ethiopia and in need of MDA by 49.1%, from 11,580,010 to 5,893,309.

Conclusion

This study demonstrated that the new confirmatory mapping tool for LF can benefit national LF programs by generating information that not only can confirm where LF is endemic, but also can save time and resources by preventing MDA where there is no evidence of ongoing LF transmission.

Lymphatic filariasis (LF) is a mosquito-borne parasitic disease, caused by 3 nematode parasites, Wuchereria bancrofti, Brugia malayi and Brugia timori. The aim of the Global Program to Eliminate LF (GPELF) is to interrupt LF transmission through mass drug administration (MDA) by 2020 and to alleviate the suffering of affected people. Mapping is the first programmatic step to determining areas of LF endemicity and establishing a national program. Ethiopia was believed to be endemic for LF, but until recently the distribution of LF in the country was unknown. From 2008–2013, mapping for LF was conducted using the current WHO protocol, and 112 woredas were identified as endemic or possibly endemic. In 45 of these 112 woredas, only a single CFA positive result was found (<1% prevalence), which called into question the stutus of transmission and need for MDA. To help resolve this uncertainty, a new confirmatory mapping tool was designed and tested in Ethiopia. The new mapping tool was piloted in the 45 woredas with uncertain LF transmission from the 2008–2013 mapping (S1 Table). This mapping confirmed that only 3 of the 45 woredas were endemic, which decreased estimated total population at risk of LF and in need of MDA from 11,580,010 to 5,893,309.

Comparison of antigen and antibody responses in repeat lymphatic filariasis transmission assessment surveys in American Samoa

Background

Current WHO recommendations for lymphatic filariasis (LF) surveillance advise programs to implement activities to monitor for new foci of transmission after stopping mass drug administration (MDA). A current need in the global effort to eliminate LF is to standardize diagnostic tools and surveillance activities beyond the recommended transmission assessment survey (TAS).

Methodology

TAS was first conducted in American Samoa in 2011 (TAS 1) and a repeat TAS was carried out in 2015 (TAS 2). Circulating filarial antigen (CFA) and serologic results from both surveys were analyzed to determine whether interruption of LF transmission has been achieved in American Samoa.

Principal findings

A total of 1,134 and 864 children (5–10 years old) were enrolled in TAS 1 and TAS 2, respectively. Two CFA-positive children were identified in TAS 1, and one CFA-positive child was identified in TAS 2. Results of both surveys were below the threshold for which MDA was warranted. Additionally, 1,112 and 836 dried blood spots from TAS 1 and TAS 2, respectively were tested for antibodies to Wb123, Bm14 and Bm33 by luciferase immunoprecipitation system (LIPS) assay and multiplex bead assay. In 2011, overall prevalence of responses to Wb123, Bm14, and Bm33 was 1.0%, 6.8% and 12.0%, respectively. In 2015, overall prevalence of positive Bm14 and Bm33 responses declined significantly to 3.0% (p<0.001) and 7.8% (p = 0.013), respectively.

Conclusions/Significance

Although passing TAS 1 and TAS 2 and an overall decline in the prevalence of antibodies to Bm14 and Bm33 between these surveys suggests decreased exposure and infection among young children, there were persistent responses in some schools. Clustering and persistence of positive antibody responses in schools may be an indication of ongoing transmission. There is a need to better understand the limitations of current antibody tests, but our results suggest that serologic tools can have a role in guiding programmatic decision making.

Lymphatic filariasis (LF), endemic in 72 countries, is a debilitating mosquito-transmitted parasitic disease caused by filarial worms. The Global Program to Eliminate Lymphatic Filariasis (GPELF) aims to interrupt transmission through mass drug administration (MDA) and to reduce suffering caused by the disease. At the start of GPELF in 2000 it was estimated that approximately 1.4 billion people were at risk for infection. By the end of 2016, primarily through successful MDA programs, the global number of people requiring interventions was reduced to 856.4 million. Current recommendations by the World Health Organization for LF surveillance advise programs to implement activities to monitor for new foci of transmission after stopping MDA. A current need in the global effort to eliminate LF is to standardize diagnostic tools and surveillance activities beyond the recommended transmission assessment survey (TAS). Two TAS were conducted in American Samoa; first in 2011 (TAS 1) and repeated in 2015 (TAS 2). In our evaluation, circulating filarial antigen and serologic results from both surveys were analyzed to determine whether interruption of LF transmission has been achieved in American Samoa. Despite passing TAS 1 and TAS 2, clustering and persistence of positive antibody responses in schools may be an indication of ongoing transmission. Results from our evaluation suggest that serologic tools can have a role in guiding programmatic decision-making.

Molecular xenomonitoring for post-validation surveillance of lymphatic filariasis in Togo: no evidence for active transmission

BACKGROUND

Lymphatic filariasis (LF) is a mosquito-borne filarial disease targeted for elimination by the year 2020. The Republic of Togo undertook mass treatment of entire endemic communities from 2000 to 2009 to eliminate the transmission of the disease and is currently the first sub-Saharan African country to be validated by WHO for the elimination of LF as a public health problem. However, post-validation surveillance activities are required to ensure the gains achieved are sustained. This survey assessed the mosquito vectors of the disease and determined the presence of infection in these vectors, testing the hypothesis that transmission has already been interrupted in Togo.

METHOD

Mosquitoes were collected from 37 villages located in three districts in one of four evaluation units in the country. In each district, 30 villages were selected based on probability proportionate to size; eight villages (including one of the 30 villages already selected) where microfilaremia-positive cases had been identified during post-treatment surveillance activities were intentionally sampled. Mosquitoes were collected using pyrethrum spray collections (PSC) in households randomly selected in all villages for five months. In the purposefully selected communities, mosquitoes were also collected using human landing collections (HLC) and exit traps (ET). Collected mosquitoes were identified morphologically, and the identification of Wuchereria bancrofti DNA in the mosquitoes was based on the pool screening method, using the LAMP assay.

RESULTS

A total of 15,539 mosquitoes were collected during the study. Anopheles gambiae (72.6%) was the predominant LF vector collected using PSC. Pool screen analysis of 9191 An. gambiae in 629 pools revealed no mosquitoes infected with W. bancrofti (0%; CI: 0-0.021).

CONCLUSIONS

These results confirm the findings of epidemiological transmission assessment surveys conducted in 2012 and 2015, which demonstrated the absence of LF transmission in Togo. The challenges of implementing molecular xenomonitoring are further discussed.

Is mass drug administration against lymphatic filariasis required in urban settings? The experience in Kano, Nigeria

Background

The Global Programme to Eliminate Lymphatic Filariasis (GPELF), launched in 2000, has the target of eliminating the disease as a public health problem by the year 2020. The strategy adopted is mass drug administration (MDA) to all eligible individuals in endemic communities and the implementation of measures to reduce the morbidity of those suffering from chronic disease. Success has been recorded in many rural endemic communities in which elimination efforts have centered. However, implementation has been challenging in several urban African cities. The large cities of West Africa, exemplified in Nigeria in Kano are challenging for LF elimination program because reaching 65% therapeutic coverage during MDA is difficult. There is therefore a need to define a strategy which could complement MDA. Thus, in Kano State, Nigeria, while LF MDA had reached 33 of the 44 Local Government Areas (LGAs) there remained eleven ‘urban’ LGAs which had not been covered by MDA. Given the challenges of achieving at least 65% coverage during MDA implementation over several years in order to achieve elimination, it may be challenging to eliminate LF in such settings. In order to plan the LF control activities, this study was undertaken to confirm the LF infection prevalence in the human and mosquito populations in three urban LGAs.

Methods

The prevalence of circulating filarial antigen (CFA) of Wuchereria bancrofti was assessed by an immuno-chromatography test (ICT) in 981 people in three urban LGAs of Kano state, Nigeria. Mosquitoes were collected over a period of 4 months from May to August 2015 using exit traps, gravid traps and pyrethrum knock-down spray sheet collections (PSC) in different households. A proportion of mosquitoes were analyzed for W. bancrofti, using dissection, loop-mediated isothermal amplification (LAMP) assay and conventional polymerase chain reaction (PCR).

Results

The results showed that none of the 981 subjects (constituted of <21% of children 5–10 years old) tested had detectable levels of CFA in their blood. Entomological results showed that An. gambiae s.l. had W. bancrofti DNA detectable in pools in Kano; W. bancrofti DNA was detected in between 0.96% and 6.78% and to a lesser extent in Culex mosquitoes where DNA was detected at rates of between 0.19% and 0.64%. DNA analysis showed that An. coluzzii constituted 9.9% of the collected mosquitoes and the remaining 90.1% of the mosquitoes were Culex mosquitoes.

Conclusion

Despite detection of W. bancrofti DNA within mosquito specimens collected in three Kano urban LGAs, we were not able to find a subject with detectable level of CFA. Together with other evidence suggesting that LF transmission in urban areas in West Africa may not be of significant importance, the Federal Ministry of Health advised that two rounds of MDA be undertaken in the urban areas of Kano. It is recommended that the prevalence of W. bancrofti infection in the human and mosquito populations be re-assessed after a couple of years.

Mass drug administration (MDA) for the control of elephantiasis in the state of Kano in Nigeria, started in the year 2010. It was estimated that by 2015, the MDA programme will be extended to 11 remaining urban Local Government Areas (LGAs). However, MDA in urban areas faces specific challenges, the most prominent being the need to achieve coverage rates of 65% and above. As such MDA alone may not be sufficient to achieve the required programme impacts of reducing LF transmission to levels below which transmission cannot be sustained, and additional interventions may be required. This study set out to confirm the LF infection prevalence in the human and mosquito populations in three urban LGAs in Kano. Individuals were tested for signs of the disease, and mosquito samples were collected and also tested for the worms that cause the disease. The study revealed that of 981 people tested, none had circulating filarial antigen in the blood. However, the mosquitoes collected revealed the presence of the disease-causing worms, but the level of infection was low. The infection in the mosquitoes was also detected in two different types of mosquitoes. Based on the outcomes of this study, and evidence from other West African cities on the transmission of LF, the Federal Ministry of Health recommended that two rounds of MDA be undertaken in urban areas of Kano. A further reassessment after a couple of years is warranted.

Lymphatic filariasis transmission on Mafia Islands, Tanzania: Evidence from xenomonitoring in mosquito vectors

Introduction

Lymphatic filariasis (LF) is a chronic nematode infection transmitted by mosquitoes and in sub-Saharan Africa it is caused by Wuchereria bancrofti. The disease was targeted for global elimination by 2020 using repeated community-wide mass drug administration (MDA) distributed in endemic areas. However, recently, there has been a growing recognition of the potential role of including vector control as a supplement to MDA to achieve elimination goal. This study was carried out to determine mosquito abundance and transmission of bancroftian filariasis on Mafia Islands in Tanzania as a prerequisite for a search for appropriate vector control methods to complement the ongoing MDA campaign.

Methods

Mosquitoes were collected indoor and outdoor using Centre for Disease Control (CDC) light and gravid traps, respectively. Collected mosquitoes were identified based on their differential morphological features and Anopheles gambiae complex and An. funestus group were further identified to their respective sibling species by polymerase chain reaction (PCR). Filarial mosquito vectors were then examined for infection with Wuchereria bancrofti by microscopy and PCR technique.

Results

Overall, a total of 35,534 filarial mosquito vectors were collected, of which Anopheles gambiae complex, An. funestus group and Culex quinquefasciatus Say accounted for 1.3, 0.5 and 98.2%, respectively. Based on PCR identification, An. gambiae sensu stricto (s.s) and An. funestus s.s sibling species accounted for 88.3% and 99.1% of the identified members of the An. gambiae complex and An. funestus group, respectively. A total of 7,936 mosquitoes were examined for infection with W. bancrofti by microscopy. The infection and infectivity rates were 0.25% and 0.08%, respectively. Using pool screen PCR technique, analysis of 324 mosquito pools (each with 25 mosquitoes) resulted to an estimated infection rate of 1.7%.

Conclusion

The study has shown that Cx. quinquefasciatus is the dominant mosquito on Mafia Islands. By using mosquito infectivity as proxy to human infection, the study indicates that W. bancrofti transmission is still ongoing on Mafia Islands after more than a decade of control activities based on MDA.

Lymphatic filariasis is a chronic human disease caused by parasitic worms and transmitted by mosquitoes. The disease is targeted for elimination by 2020 through the treatment of the entire population at risk in endemic areas using a mass drug administration (MDA) strategy. After several years of MDA, there is now growing interest in including vector control as a supplement to MDA to achieve elimination goal. This study was carried out to determine mosquito abundance and transmission of lymphatic filariasis on Mafia Islands in Tanzania after nine rounds of MDA. Mosquitoes were collected indoor and outdoor using Centre for Disease Control (CDC) light and gravid traps, respectively. Filarial mosquito vectors were examined for infection with Wuchereria bancrofti by microscopy and PCR technique. A total of 35,534 filarial mosquito vectors were collected, of which Anopheles gambiae complex, An. funestus group and Culex quinquefasciatus Say accounted for 1.3, 0.5 and 98.2%, respectively. Using PCR, An. gambiae sensu stricto (s.s) and An. funestus s.s sibling species accounted for 88.3% and 99.1% of the identified members of the An. gambiae complex and An. funestus group, respectively. A total of 7,936 mosquitoes were examined for infection with W. bancrofti by microscopy. The infection and infectivity rates were 0.25% and 0.08%, respectively. Using PCR technique, of 324 mosquito pools (each with 25 mosquitoes) tested, 115 were found to be infected with at least a larval stage of W. bancrofti. The study concludes that Cx. quinquefasciatus is the dominant mosquito on Mafia Islands and that W. bancrofti transmission is still ongoing on Mafia Islands after a decade of control activities based on MDA.

Community-based trial of annual versus biannual single-dose ivermectin plus albendazole against Wuchereria bancrofti infection in human and mosquito populations: study protocol for a cluster randomised controlled trial

BACKGROUND

The Global Programme for the Elimination of Lymphatic Filariasis (GPELF) has been in operation since the year 2000, with the aim of eliminating the disease by the year 2020, following five to six rounds of effective annual mass drug administration (MDA). The treatment regimen is ivermectin (IVM) in combination with diethylcarbamazine (DEC) or albendazole (ALB). In Ghana, MDA has been undertaken since 2001. While the disease has been eliminated in many areas, transmission has persisted in some implementation units that had experienced 15 or more rounds of MDA. Thus, new intervention strategies could eliminate residual infection in areas of persistent transmission and speed up the lymphatic filariasis (LF)-elimination process. This study, therefore, seeks to test the hypothesis that biannual treatment of LF-endemic communities will accelerate the interruption of LF in areas of persistent transmission.

METHODS

A cluster randomised trial will be implemented in LF-endemic communities in Ghana. The interventions will be yearly or twice-yearly MDA delivered to entire endemic communities. Allocation to study group will be by clusters identified using the prevalence of LF. Clusters will be randomised to one of two groups: receiving either (1) annual treatment with IVM + ALB or (2) annual MDA with IVM + ALB, followed by an additional MDA 6 months later. The primary outcome measure is the prevalence of LF infection, assessed by four cross-sectional surveys. Entomological assessments will also be undertaken to evaluate the transmission intensity of the disease in the study clusters. Costs and cost-effectiveness will be evaluated. Among a random subsample of participants, microfilaria prevalence will be assessed longitudinally. A nested process evaluation, using semi-structured interviews, focus group discussions and a stakeholder analysis, will investigate the community acceptability, feasibility and scale-up of each delivery system.

DISCUSSION

It is expected that this study will add to the existing evidence on the need for alternative intervention strategies for the elimination of LF in Ghana and in other African countries that are facing similar challenges or are at the beginning of their LF-elimination programmes.

TRIAL REGISTRATION

ClinicalTrials.gov, ID: NCT03036059 . Registered on 26 January 2017. Pan African Clinical Trials Registry, ID: PACTR201702002012425 . Registered on 23 February 2017.

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.

Impact of mass drug administration for elimination of lymphatic filariasis in Nepal

Background

Lymphatic filariasis (LF) is a neglected tropical disease transmitted by mosquitoes. Nepal has implemented a national effort to eliminate LF by 2020 through mass drug administration (MDA) using diethylcarbamazine (DEC) and albendazole (ALB). We assessed the impact of MDAs on LF in selected districts of Nepal after the recommended six MDA rounds had been completed.

Methodology and principal findings

Baseline surveys were conducted in seven districts and mapping data were used as baseline in the other three districts before starting MDA in 2009. LF antigen (Ag) prevalence ranged from 1.06% to 20% among districts included in the baseline and mapping study. The number of people who received DEC and ALB were recorded during each MDA round and population-based cluster surveys were conducted at least once in each district during the life of the program. The reported MDA coverage in five districts was consistently at least 65%. Two districts achieved the targeted coverage in four out of five rounds and the rest three districts achieved the target only in the first round. A pre-transmission assessment survey (pre-TAS) was conducted in one sentinel site and at least one spot check site in each of the districts after five MDA rounds. In pre-TAS, all the sites of five districts (Pyuthan, Arghakhanchi, Kaski, Bhaktapur, and Kathmandu) and all but one spot check site of Lalitpur district had LF Ag < 2% (ranging from 0.0% to 1.99%). Transmission assessment survey (TAS) was conducted in six evaluation units (EUs) consisting of six districts qualified on pre-TAS. Though MDA coverage of 65% was not achieved in three districts (Kathmandu, Lalitpur and Bhaktapur), Nepal government in consultation with World Health Organization (WHO) decided to conduct TAS. All six EUs achieved the LF Ag threshold required to stop MDA in TAS, despite the low reported MDA coverage in those three districts.

Conclusions

Although Nepal has achieved significant progress towards LF elimination, five rounds of MDA were not sufficient to disrupt the transmission cycle in all districts, probably because of high baseline prevalence.

Lymphatic filariasis (LF) is a deforming and disabling infectious disease manifested in the form of elephantiasis and hydroceles. Based on mapping data, 61 out of 75 districts of Nepal were found to be endemic for LF and mass drug administration (MDA) of diethylcarbamazine and albendazole has been already started in 56 districts. The objective of MDA is to interrupt transmission of Wuchereria bancrofti in LF endemic districts. In 2015, ten districts had completed six MDA rounds. In this study we reported the impact of the national LF elimination effort in these ten districts of Nepal. The reported coverage rate in each MDA round was consistently above 65% in five districts. Compared to the baseline surveys, pre-transmission assessment surveys (pre-TAS) conducted after completion of five MDA rounds showed reductions in LF antigenemia (Ag) in most districts. Six out of ten districts (formed into six evaluation units) were eligible for TAS, which showed LF Ag below the cutoff point in all six EUs, suggesting successful interruption of LF transmission in six out of ten districts after six MDA rounds.

First evidence of lymphatic filariasis transmission interruption in Cameroon: Progress towards elimination

BACKGROUND

Lymphatic filariasis (LF) is among the 10 neglected tropical diseases targeted for control or elimination by 2020. For LF elimination, the World Health Organization (WHO) has proposed a comprehensive strategy including (i) interruption of LF transmission through large-scale annual treatment (or mass drug administration (MDA)) of all eligible individuals in endemic areas, and (ii) alleviation of LF-associated suffering through morbidity management and disability prevention. In Cameroon, once-yearly mass administration of ivermectin and albendazole has been implemented since 2008. The aim of this study was to assess progress towards the elimination goal, looking specifically at the impact of six rounds of MDA on LF transmission in northern Cameroon.

METHODOLOGY

The study was conducted in the North and Far North Regions of Cameroon. Five health districts that successfully completed six rounds of MDA (defined as achieving a treatment coverage ≥ 65% each year) and reported no positive results for Wuchereria bancrofti microfilariaemia during routine surveys following the fifth MDA were grouped into three evaluation units (EU) according to WHO criteria. LF transmission was assessed through a community-based transmission assessment survey (TAS) using an immunochromatographic test (ICT) for the detection of circulating filarial antigen (CFA) in children aged 5-8 years old.

PRINCIPAL FINDINGS

A total of 5292 children (male/female ratio 1.04) aged 5-8 years old were examined in 97 communities. Positive CFA results were observed in 2, 8 and 11 cases, with a CFA prevalence of 0.13% (95% CI: 0.04-0.46) in EU#1, 0.57% (95% CI: 0.32-1.02) in EU#2, and 0.45% (95% CI: 0.23-0.89) in EU#3.

CONCLUSION/SIGNIFICANCE

The positive CFA cases were below WHO defined critical cut-off thresholds for stopping treatment and suggest that transmission can no longer be sustained. Post-MDA surveillance activities should be organized to evaluate whether recrudescence can occur.

Partnering for impact: Integrated transmission assessment surveys for lymphatic filariasis, soil transmitted helminths and malaria in Haiti

Background

Since 2001, Haiti’s National Program for the Elimination of Lymphatic Filariasis (NPELF) has worked to reduce the transmission of lymphatic filariasis (LF) through annual mass drug administration (MDA) with diethylcarbamazine and albendazole. The NPELF reached full national coverage with MDA for LF in 2012, and by 2014, a total of 14 evaluation units (48 communes) had met WHO eligibility criteria to conduct LF transmission assessment surveys (TAS) to determine whether prevalence had been reduced to below a threshold, such that transmission is assumed to be no longer sustainable. Haiti is also endemic for malaria and many communities suffer a high burden of soil transmitted helminths (STH). Heeding the call from WHO for integration of neglected tropical diseases (NTD) activities, Haiti’s NPELF worked with the national malaria control program (NMCP) and with partners to develop an integrated TAS (LF-STH-malaria) to include assessments for malaria and STH.

Methodology/Principle findings

The aim of this study was to evaluate the feasibility of using TAS surveys for LF as a platform to collect information about STH and malaria. Between November 2014 and June 2015, TAS were conducted in 14 evaluation units (EUs) including 1 TAS (LF-only), 1 TAS-STH-malaria, and 12 TAS-malaria, with a total of 16,655 children tested for LF, 14,795 tested for malaria, and 298 tested for STH. In all, 12 of the 14 EUs passed the LF TAS, allowing the program to stop MDA for LF in 44 communes. The EU where children were also tested for STH will require annual school-based treatment with albendazole to maintain reduced STH levels. Finally, only 12 of 14,795 children tested positive for malaria by RDT in 38 communes.

Conclusions/Significance

Haiti’s 2014–2015 Integrated TAS surveys provide evidence of the feasibility of using the LF TAS as a platform for integration of assessments for STH and or malaria.

Lymphatic filariasis and malaria are mosquito-borne parasitic infections that are endemic in Haiti. Soil-transmitted helminths are also present in Haiti, infecting large numbers of people every year. Since 2001, Haiti’s National Program for the Elimination of Lymphatic Filariasis (NPELF) has worked to reduce the transmission of LF through annual mass drug administration with the aim of reducing LF prevalence in the population below a threshold, such that transmission is assumed to be no longer sustainable. By treating the entire population of Haiti with a combination of drugs, the elimination program has made tremendous progress towards eliminating the disease. By 2014, Haiti’s NPELF had met the World Health Organization eligibility criteria to conduct LF transmission assessment surveys (TAS) and decided to use the LF TAS as a platform to collect information about STH and malaria. The WHO has called for the integration of program activities in the field, and the TAS is a platform that allows for such integration. In Haiti the integrated TAS reduced the burden of repeated surveys on communities by minimizing site visits and benefited all three disease programs by sharing the responsibilities of field data collection.

Costs of Transmission Assessment Surveys to Provide Evidence for the Elimination of Lymphatic Filariasis

Background

To reach the global goal of elimination of lymphatic filariasis as a public health problem by 2020, national programs will have to implement a series of transmission assessment surveys (TAS) to determine prevalence of the disease by evaluation unit. It is expected that 4,671 surveys will be required by 2020. Planning in advance for the costs associated with these surveys is essential to ensure that the required resources are available for this essential program activity.

Methodology and Findings

Retrospective cost data was collected from reports from 13 countries which implemented a total of 105 TAS surveys following a standardized World Health Organization (WHO) protocol between 2012 and 2014. The median cost per survey was $21,170 (including the costs for rapid diagnostic tests [RDTs]) and $9,540 excluding those costs. Median cost per cluster sampled (without RDT costs) was $101. Analysis of costs (excluding RDTs) by category showed that the main cost drivers were personnel and travel.

Conclusion

Transmission assessment surveys are critical to collect evidence to validate elimination of LF as a public health problem. National programs and donors can use the costing results to adequately plan and forecast the resources required to undertake the necessary activities to conduct high-quality transmission assessment surveys.

As national programs are nearing elimination of lymphatic filariasis as a public health problem, questions have been raised about the cost of collecting the data necessary for documenting validation of elimination. A series of standardized population-based surveys is necessary to determine prevalence of infection in endemic areas. The authors retrospectively collected data on the costs of these surveys from 13 countries to determine median cost per survey and per cluster sampled. Costs were found to be comparable with other neglected tropical disease surveys. The major cost drivers were personnel and travel for supporting collection of data in the field. National programs and donors can use these results to plan and advocate more effectively for sufficient resources to support validation of elimination.

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.

The Impact of Lymphatic Filariasis Mass Drug Administration Scaling Down on Soil-Transmitted Helminth Control in School-Age Children. Present Situation and Expected Impact from 2016 to 2020

Lymphatic filariasis (LF) and soil-transmitted-helminths (STH) are co-endemic in 58 countries which are mostly in Africa and Asia. Worldwide, 486 million school-age children are considered at risk of both diseases. In 2000, the World Health Organization (WHO) established the global programme to eliminate LF by 2020. Since then, the LF elimination programme has distributed ivermectin or diethylcarbamazine citrate (DEC) in combination with albendazole, thereby also treating STH. Consequently, many school-age children have been treated for STH through the LF programme. As treatment targets towards the 2020 LF elimination goal are achieved, many countries are implementing the transmission assessment survey (TAS) and, if the LF prevalence is estimated to be less than 1%, scaling down mass drug administration (MDA). We analysed the 2014 data on preventive chemotherapy (PC) reported from LF STH co-endemic countries and projected the year and location of TAS expected to be conducted between 2016 and 2020 to assess the impact of this scaling down on STH PC. Eighty percent of all co-endemic countries that have already stopped LF MDA nationally were able to establish STH PC through schools. It is estimated that 14% of the total number of children presently covered by the LF programme is at risk of not continuing to receive PC for STH. In order to achieve and maintain the WHO 2020 goal for STH control, there is an urgent need to establish and reinforce school-based deworming programmes in countries scaling-down national LF elimination programmes.

Lymphatic filariasis (LF) and soil-transmitted helminths (STH) (i.e. intestinal worms) are two tropical diseases that are found together in 58 countries in the world. School-age children are most affected by intestinal worms, albendazole, one of the two drugs used for LF, also treats STH. For this reason, large-scale delivery of LF drugs in the community has been used as a means to also treat school-age children for intestinal worm infections in many countries. In line with the WHO goal to eliminate LF by 2020, countries that have achieved that objective have started stopping community-based LF treatment. Therefore, we analysed treatment data from 2014 to quantify the effect of this reduction on treatment of school-age children for intestinal worms. The results show that 80% of countries that have already stopped LF treatment were able to administer deworming drugs for STH to school-age children within school-based treatment programmes. There is an urgent need to continue to establish and strengthen deworming through school health programmes in endemic countries in order to meet the WHO established goal to treat at least 75% of at risk school-age children for STH by 2020.

INVESTIGATION OF MOSQUITOES WITH EMPHASIS ON AEDES (FINLAYA) POICILIUS, PUTATIVE VECTOR OF BANCROFTIAN FILARIASIS ON PANAY ISLAND, THE PHILIPPINES

Entomological investigations were conducted in four remaining lymphatic filariasis endemic provinces of Panay Island, The Philippines to determine mosquito species present in these areas and to identify host preference and biting activity of Aedes (Finlaya) poicilius Theobald, primary vector of nocturnal periodic Wuchereria bancrofti in The Philippines. Sampling techniques targeted nocturnally active mosquito species using a carabao-baited trap (CBT) and human-landing collection (HLC), the latter taking place from 06:00 to 12:00 pm. A total of 25,536 mosquitoes comprising 42 species and 7 genera were collected from CBT, whilst HLC acquired 6,486 mosquitoes comprising 28 species and 5 genera. Three known or potential vectors of human filarial were collected, namely, Aedes poicilius, Culex quinquefasciatus and Mansonia uniformis. The peak landing (biting) activity for Ae. poicilius was between 09:00 and 11:00 pm. Comparisons between CBT and HLC yields showed this species to be more zoophilic. Based on observed mosquito behavior and interviews with residents, vector-host contact was promoted by the local practice of staying overnight in makeshift shelters in high risk areas without adequate protection against mosquito bites. Results of this survey will augment information for integrating vector control and mass drug administration into an island-wide lymphatic filariasis elimination program.

Programmatic Use of Molecular Xenomonitoring at the Level of Evaluation Units to Assess Persistence of Lymphatic Filariasis in Sri Lanka

BACKGROUND

Sri Lanka's Anti Filariasis Campaign distributed 5 rounds of mass drug administration (MDA with DEC plus albendazole) to all endemic regions in the country from 2002-2006. Post-MDA surveillance results have generally been encouraging. However, recent studies have documented low level persistence of Wuchereria bancrofti in Galle district based on comprehensive surveys that include molecular xenomonitoring (MX, detection of filarial DNA in mosquitoes) results. The purposes of this study were to demonstrate the use of MX in large evaluation units (EUs) and to field test different mosquito sampling schemes.

METHODOLOGY/PRINCIPAL FINDINGS

Galle district (population 1.1 million) was divided into two EUs. These included a coastal EU with known persistent LF and an inland EU with little persistent LF. Mosquitoes were systematically sampled from ~300 trap locations in 30 randomly selected clusters (health administrative units) per EU. Approximately 28,000 Culex quinquefasciatus were collected with gravid traps and tested for filarial DNA by qPCR. 92/625 pools (14.7%) from the coastal EU and 8/583 pools (1.4%) from the inland EU were positive for filarial DNA. Maximum likelihood estimates (MLE) for filarial DNA rates were essentially the same when the same number of mosquito pools were collected and tested from 75, 150, or 300 trap sites (range 0.61-0.78% for the coastal EU and 0.04-0.07% for the inland EU). The ability to use a smaller number of trap sites reduces the cost and time required for mosquito sampling.

CONCLUSIONS/SIGNIFICANCE

These results suggest there is widespread persistence of W. bancrofti infection in the coastal Galle EU 8 years after the last round of MDA in 2006, and this is consistent with other data from the district. This study has shown that MX can be used by national programs to assess and map the persistence of W. bancrofti at the level of large EUs in areas with Culex transmission.

Successful Control of Soil-Transmitted Helminthiasis in School Age Children in Burkina Faso and an Example of Community-Based Assessment via Lymphatic Filariasis Transmission Assessment Survey

Background

Burkina Faso is endemic with soil-transmitted helminth infections. Over a decade of preventive chemotherapy has been implemented through annual lymphatic filariasis (LF) mass drug administration (MDA) for population aged five years and over, biennial treatment of school age children with albendazole together with schistosomiasis MDA and biannual treatment of pre-school age children through Child Health Days. Assessments were conducted to evaluate the current situation and to determine the treatment strategy for the future.

Methodology/Principal Findings

A cross-sectional assessment was conducted in 22 sentinel sites across the country in 2013. In total, 3,514 school age children (1,748 boys and 1,766 girls) were examined by the Kato-Katz method. Overall, soil-transmitted helminth prevalence was 1.3% (95% CI: 1.0–1.8%) in children examined. Hookworm was the main species detected, with prevalence of 1.2% (95% CI: 0.9–1.6%) and mean egg counts of 2.1 epg (95% CI: 0–4.2 epg). Among regions, the Centre Ouest region had the highest hookworm prevalence of 3.4% (95% CI: 1.9–6.1%) and mean egg counts of 14.9 epg (95% CI: 3.3–26.6 epg). A separate assessment was conducted in the Centre Nord region in 2014 using community-based cluster survey design during an LF transmission assessment survey (TAS). In this assessment, 351 children aged 6–7 years and 345 children aged 10–14 years were examined, with two cases (0.6% (95% CI: 0.2–2.1%)) and seven cases (2.0% (95% CI: 1.0–4.1%)) of hookworm infection was identified respectively. The results using both age groups categorized the region to be 2% to <10% in STH prevalence according to the pre-defined cut-off values.

Conclusions/Significance

Through large-scale preventive chemotherapy, Burkina Faso has effectively controlled STH in school age children in the country. Research should be conducted on future strategies to consolidate the gain and to interrupt STH transmission in Burkina Faso. It is also demonstrated that LF TAS provides one feasible and efficient platform to assess the STH situation for post LF MDA decision making.

Burkina Faso is a West African country endemic with soil-transmitted helminth infections (STH). Mass treatment with albendazole has been implemented for over a decade in the country through annual mass drug administration (MDA) for lymphatic filariasis for population aged five years and over, biennial treatment of school age children with albendazole together with schistosomiasis MDA, and biannual treatment of pre-school age children through Child Health Days. A sentinel site survey in 2013 showed that STH infection in Burkina Faso was very low at 1.3%. Hookworm was the main species detected, but infection was low and light. An assessment was also conducted with two age groups in Centre Nord region through lymphatic filariasis transmission assessment survey in 2014. The results confirmed the low level of infection with soil-transmitted helminths in the region. Through large-scale preventive chemotherapy, Burkina Faso has effectively controlled STH in school age children in the country. The future STH deworming strategy may focus on consolidating the gain and interrupting the STH transmission in the country.

Prevalence of lymphatic filariasis in a tea garden worker population of Dibrugarh (Assam), India after six rounds of mass drug administration

BACKGROUND & OBJECTIVES

Lymphatic filariasis (LF) is endemic in the state of Assam and mass drug administration (MDA) programme for LF elimination is being implemented in the state since 2004. A study on prevalence of microfilaria (mf), disease endemicity and vector infection was carried out in a tea garden population of Dibrugarh, Assam (India) to assess the effect of ongoing MDA programme on elimination of LF.

METHODS

Finger prick thick blood smears (20 mm3) were made from individuals aged ≥2 yr old during night blood survey in between 2000-0000 hrs during the period of November 2012 to February 2013. Blood smears were dehaemoglobinised, stained with Giemsa and examined under microscope for presence of mf. Indoor resting mosquitoes were collected during 0600-1000 hrs and female Culex quinquefasciatus were dissected and examined under microscope for larval forms of the parasite.

RESULTS

A total of 634 blood smears were collected and screened for mf and 47 (7.41%) individuals were found microfilaraemic, with predominance of males (74.5%). Highest mf rate (20.0%) was seen in the males of 30-39 yr age group while in females, age group of 10-19 yr recorded maximum mf rate (5.48%). Entomological collection and dissection of Cx. quinquefasciatus revealed presence of larval stages of the parasite and infection and infectivity rates recorded were 13.20 and 3.70%, respectively. Chronic clinical manifestations in the form of elephantiasis and hydrocele were recorded in 33 (5.73%) subjects of the 575 examined.

INTERPRETATION & CONCLUSION

Mass drug administration data showed six rounds of MDA with drug distribution coverage in between 63.42 and 95.93% in the study population. Out of 634 individuals examined 47 were found microfilaraemic giving an overall infection rate of 7.41%. Mosquito vector infection and infectivity rates were 13.20 and 3.70%, respectively. Presence of high mf rate, vector infectivity rate and clinical cases in the study population after six rounds of MDA warrants concerted efforts to be made for effective implementation and monitoring of MDA for success of LF elimination programme.

Comparison of Methods for Xenomonitoring in Vectors of Lymphatic Filariasis in Northeastern Tanzania

Monitoring Wuchereria bancrofti infection in mosquitoes (xenomonitoring) can play an important role in determining when lymphatic filariasis has been eliminated, or in focusing control efforts. As mosquito infection rates can be low, a method for collecting large numbers of mosquitoes is necessary. Gravid traps collected large numbers of Culex quinquefasciatus in Tanzania, and a collection method that targets mosquitoes that have already fed could result in increased sensitivity in detecting W. bancrofti-infected mosquitoes. The aim of this experiment was to test this hypothesis by comparing U.S. Centers for Disease Control and Prevention (CDC) light traps with CDC gravid traps in northeastern Tanzania, where Cx. quinquefasciatus is a vector of lymphatic filariasis. After an initial study where small numbers of mosquitoes were collected, a second study collected 16,316 Cx. quinquefasciatus in 60 gravid trap-nights and 240 light trap-nights. Mosquitoes were pooled and tested for presence of W. bancrofti DNA. Light and gravid traps collected similar numbers of mosquitoes per trap-night, but the physiological status of the mosquitoes was different. The estimated infection rate in mosquitoes collected in light traps was considerably higher than in mosquitoes collected in gravid traps, so light traps can be a useful tool for xenomonitoring work in Tanzania.

Modelling strategies to break transmission of lymphatic filariasis--aggregation, adherence and vector competence greatly alter elimination

BACKGROUND

With ambitious targets to eliminate lymphatic filariasis over the coming years, there is a need to identify optimal strategies to achieve them in areas with different baseline prevalence and stages of control. Modelling can assist in identifying what data should be collected and what strategies are best for which scenarios.

METHODS

We develop a new individual-based, stochastic mathematical model of the transmission of lymphatic filariasis. We validate the model by fitting to a first time point and predicting future timepoints from surveillance data in Kenya and Sri Lanka, which have different vectors and different stages of the control programme. We then simulate different treatment scenarios in low, medium and high transmission settings, comparing once yearly mass drug administration (MDA) with more frequent MDA and higher coverage. We investigate the potential impact that vector control, systematic non-compliance and different levels of aggregation have on the dynamics of transmission and control.

RESULTS

In all settings, increasing coverage from 65 to 80 % has a similar impact on control to treating twice a year at 65 % coverage, for fewer drug treatments being distributed. Vector control has a large impact, even at moderate levels. The extent of aggregation of parasite loads amongst a small portion of the population, which has been estimated to be highly variable in different settings, can undermine the success of a programme, particularly if high risk sub-communities are not accessing interventions.

CONCLUSION

Even moderate levels of vector control have a large impact both on the reduction in prevalence and the maintenance of gains made during MDA, even when parasite loads are highly aggregated, and use of vector control is at moderate levels. For the same prevalence, differences in aggregation and adherence can result in very different dynamics. The novel analysis of a small amount of surveillance data and resulting simulations highlight the need for more individual level data to be analysed to effectively tailor programmes in the drive for elimination.

Climate Change and Spatiotemporal Distributions of Vector-Borne Diseases in Nepal--A Systematic Synthesis of Literature

Background

Despite its largely mountainous terrain for which this Himalayan country is a popular tourist destination, Nepal is now endemic for five major vector-borne diseases (VBDs), namely malaria, lymphatic filariasis, Japanese encephalitis, visceral leishmaniasis and dengue fever. There is increasing evidence about the impacts of climate change on VBDs especially in tropical highlands and temperate regions. Our aim is to explore whether the observed spatiotemporal distributions of VBDs in Nepal can be related to climate change.

Methodology

A systematic literature search was performed and summarized information on climate change and the spatiotemporal distribution of VBDs in Nepal from the published literature until December2014 following providing items for systematic review and meta-analysis (PRISMA) guidelines.

Principal Findings

We found 12 studies that analysed the trend of climatic data and are relevant for the study of VBDs, 38 studies that dealt with the spatial and temporal distribution of disease vectors and disease transmission. Among 38 studies, only eight studies assessed the association of VBDs with climatic variables. Our review highlights a pronounced warming in the mountains and an expansion of autochthonous cases of VBDs to non-endemic areas including mountain regions (i.e., at least 2,000 m above sea level). Furthermore, significant relationships between climatic variables and VBDs and their vectors are found in short-term studies.

Conclusion

Taking into account the weak health care systems and difficult geographic terrain of Nepal, increasing trade and movements of people, a lack of vector control interventions, observed relationships between climatic variables and VBDs and their vectors and the establishment of relevant disease vectors already at least 2,000 m above sea level, we conclude that climate change can intensify the risk of VBD epidemics in the mountain regions of Nepal if other non-climatic drivers of VBDs remain constant.

Toxicity of some plant extracts against vector of lymphatic filariasis, Culex pipiens

Many insecticides are generally used as larvicides to control Culex pipiens, vector of lymphatic filariasis. This study was undertaken to evaluate the larvicidal activity of some potential larvicidal plants extracts against C. pipiens larvae. The toxic effects of both ethanolic and petroleum ether plant extracts were evaluated under laboratory conditions against 3rd instar larvae of C. pipiens. Forty ethanolic and petroleum ether extracts of 10 plants namely Echinochloa stagninum, Phragmites australis, Eichhornia crassipes, Rhizophora mucronata, Cichorium intybus, Ocimum basilicum, Origanum majorana, Azadirachta indica, Rosmarinus officinalis and Nigella sativa. On the basis of LC50, the toxic effect of the plant extracts tested varied depending on the plant species, part, solvent used in extraction and the extract concentrations. The petroleum ether extraction was more effective against mosquito as compared with ethanolic extraction. The most effective plant extract was A. indica followed by Ph. australis, N. sativa, C. intybus, R. officinalis, O. basilicum, O. majorana, E. stagninum, Rh. Mucronata and E. crassipes.

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

BACKGROUND

Lymphatic filariasis (LF) is targeted for elimination through annual mass drug administration (MDA) for 4-6 years. In 2006, Zanzibar stopped MDA against LF after five rounds of MDA revealed no microfilaraemic individuals during surveys at selected sentinel sites. We asked the question if LF transmission was truly interrupted in 2006 when MDA was stopped.

METHODOLOGY/PRINCIPAL FINDINGS

In line with ongoing efforts to shrink the LF map, we performed the WHO recommended transmission assessment surveys (TAS) in January 2012 to verify the absence of LF transmission on the main Zanzibar islands of Unguja and Pemba. Altogether, 3275 children were tested on both islands and 89 were found to be CFA positive; 70 in Pemba and 19 in Unguja. The distribution of schools with positive children was heterogeneous with pronounced spatial variation on both islands. Based on the calculated TAS cut-offs of 18 and 20 CFA positive children for Pemba and Unguja respectively, we demonstrated that transmission was still ongoing in Pemba where the cut-off was exceeded.

CONCLUSIONS

Our findings indicated ongoing transmission of LF on Pemba in 2012. Moreover, we presented evidence from previous studies that LF transmission was also active on Unguja shortly after stopping MDA in 2006. Based on these observations the government of Zanzibar decided to resume MDA against LF on both islands in 2013.

Factors associated with the performance and cost-effectiveness of using lymphatic filariasis transmission assessment surveys for monitoring soil-transmitted helminths: a case study in Kenya

Transmission assessment surveys (TAS) for lymphatic filariasis have been proposed as a platform to assess the impact of mass drug administration (MDA) on soil-transmitted helminths (STHs). This study used computer simulation and field data from pre- and post-MDA settings across Kenya to evaluate the performance and cost-effectiveness of the TAS design for STH assessment compared with alternative survey designs. Variations in the TAS design and different sample sizes and diagnostic methods were also evaluated. The district-level TAS design correctly classified more districts compared with standard STH designs in pre-MDA settings. Aggregating districts into larger evaluation units in a TAS design decreased performance, whereas age group sampled and sample size had minimal impact. The low diagnostic sensitivity of Kato-Katz and mini-FLOTAC methods was found to increase misclassification. We recommend using a district-level TAS among children 8-10 years of age to assess STH but suggest that key consideration is given to evaluation unit size.

Molecular epidemiology, phylogeny and evolution of the filarial nematode Wuchereria bancrofti

Wuchereria bancrofti (Wb) is the most widely distributed of the three nematodes known to cause lymphatic filariasis (LF), the other two being Brugia malayi and Brugia timori. Current tools available to monitor LF are limited to diagnostic tests targeting DNA repeats, filarial antigens, and anti-filarial antibodies. While these tools are useful for detection and surveillance, elimination programs have yet to take full advantage of molecular typing for inferring infection history, strain fingerprinting, and evolution. To date, molecular typing approaches have included whole mitochondrial genomes, genotyping, targeted sequencing, and random amplified polymorphic DNA (RAPDs). These studies have revealed much about Wb biology. For example, in one study in Papua New Guinea researchers identified 5 major strains that were widespread and many minor strains some of which exhibit geographic stratification. Genome data, while rare, has been utilized to reconstruct evolutionary relationships among taxa of the Onchocercidae (the clade of filarial nematodes) and identify gene synteny. Their phylogeny reveals that speciation from the common ancestor of both B. malayi and Wb occurred around 5-6 millions years ago with shared ancestry to other filarial nematodes as recent as 15 million years ago. These discoveries hold promise for gene discovery and identifying drug targets in species that are more amenable to in vivo experiments. Continued technological developments in whole genome sequencing and data analysis will likely replace many other forms of molecular typing, multiplying the amount of data available on population structure, genetic diversity, and phylogenetics. Once widely available, the addition of population genetic data from genomic studies should hasten the elimination of LF parasites like Wb. Infectious disease control programs have benefited greatly from population genetics data and recently from population genomics data. However, while there is currently a surplus of data for diseases like malaria and HIV, there is a scarcity of this data for filarial nematodes. With the falling cost of genome sequencing, research on filarial nematodes could benefit from the addition of population genetics statistics and phylogenetics especially in dealing with elimination programs. A comprehensive review focusing on population genetics of filarial nematode does not yet exist. Here our goal is to provide a current overview of the molecular epidemiology of W. bancrofti (Wb) the primary causative agent of LF. We begin by reviewing studies utilizing molecular typing techniques with specific focus on genomic and population datasets. Next, we used whole mitochondrial genome data to construct a phylogeny and examine the evolutionary history of the Onchocercidae. Then, we provide a perspective to aid in understanding how population genetic techniques translate to modern epidemiology. Finally, we introduce the concept of genomic epidemiology and provide some examples that will aid in future studies of Wb.