Impact of MDA and the prospects of elimination of the lone focus of diurnally sub periodic lymphatic filariasis in Nicobar Islands, India

Drug associations as alternative and complementary therapy for neglected tropical diseases

The present paper aims to establish different treatments for neglected tropical disease by a survey on drug conjugations and possible fixed-dose combinations (FDC) used to obtain alternative, safer and more effective treatments. The source databases used were Science Direct and PubMed/Medline, in the intervals between 2015 and 2021 with the drugs key-words or diseases, like "schistosomiasis", "praziquantel", "malaria", "artesunate", "Chagas' disease", "benznidazole", "filariasis", diethylcarbamazine", "ivermectin", " albendazole". 118 works were the object of intense analysis, other articles and documents were used to increase the quality of the studies, such as consensuses for harmonizing therapeutics and historical articles. As a result, an effective NTD control can be achieved when different public health approaches are combined with interventions guided by the epidemiology of each location and the availability of appropriate measures to detect, prevent and control disease. It was also possible to verify that the FDCs promote a simplification of the therapeutic regimen, which promotes better patient compliance and enables a reduction in the development of parasitic resistance, requiring further studies aimed at resistant strains, since the combined APIs usually act by different mechanisms or at different target sites. In addition to eliminating the process of developing a new drug based on the identification and validation of active compounds, which is a complex, long process and requires a strong long-term investment, other advantages that FDCs have are related to productive gain and gain from the industrial plant, which can favor and encourage the R&D of new FDCs not only for NTDs but also for other diseases that require the use of more than one drug.

Heterogeneous response of Wuchereria bancrofti-infected persons to diethylcarbamazine (DEC) and its implications for the Global Programme to Eliminate Lymphatic Filariasis (GPELF)

DEC or ivermectin (IVM) in combination with albendazole (ALB) has been the recommended strategy of the Global Programme to Eliminate Lymphatic Filariasis (GPELF) since 2000. Despite effective population coverage (> 65%) with several rounds of MDA with DEC or combination of DEC plus ALB, microfilariae persist in few individuals and they continue to be the source of infection for transmitting LF. We report an individual's variability in response to DEC by defining the response as complete absence of microfilaria (mf) (post-treatment mf count = 0) and non-response as presence of mf (post-treatment mf count ≥ 1). We analyzed follow-up data on individual's response to treatment from two randomized clinical trials in which 46 microfilaremic individuals were treated with single-dose DEC (6 mg/kg body weight). They were classified into low, medium, and high mf density categories based on their pre-treatment mf counts. Of the 46 individuals, 65.2% have not responded throughout the 12-month post-treatment period. Application of a logistic regression model with fixed (age, gender, mf density, post-treatment time, and their interactions) and random (individual's response over time) effects indicated that treatment response is independent of age, gender, and time. The overall treatment response increases in low and decreases in high mf density categories. Furthermore, the estimates for the random coefficients model showed that there is a greater variability in response between individuals over post-treatment time. The results substantiate that individual variation in response to DEC exists which indicate the importance of studying the parasite as well as host genetic factors associated with DEC action.

Molecular xenomonitoring of diurnally subperiodic Wuchereria bancrofti infection in Aedes (Downsiomyia) niveus (Ludlow, 1903) after nine rounds of Mass Drug Administration in Nancowry Islands, Andaman and Nicobar Islands, India

A group of four human inhabited Nancowry Islands in Nicobar district in the Andaman and Nicobar Islands, India having a population of 7674 is the lone focus of diurnally sub-periodic Wuchereria bancrofti (DspWB) that is transmitted by Aedes niveus (Ludlow). Microfilaria (Mf) prevalence was above 1% even after nine rounds of Mass Drug Administration (MDA) with DEC and albendazole. Molecular xenomonitoring (MX) was conducted to identify appropriate vector sampling method and assess the impact. BioGents Sentinel traps, gravid traps and human baited double bed nettraps were used in three locations in each village to collect Aedes niveus female mosquitoes. Subsequently daytime man landing collections (MLC) were carried out in all the 25 villages in the islands. Collections were compared in terms of the number of vector mosquitoes captured per trap collection. Females of Ae. niveus were pooled, dried and processed for detecting filarial parasite DNA using RT-PCR assay. Vector infection rate was estimated using PoolScreen software. Only 393 female mosquitoes including 44 Ae. niveus (11.2%) were collected from 459 trap collections using three trapping devices. From 151 MLCs, 2170 Ae. niveus female mosquitoes were collected. The average prevalence of W. bancrofti DNA was 0.43%. Estimated upper 95% CI exceeded the provisional prevalence threshold of 0.1% in all the villages, indicating continued transmission as observed in Mf survey. MLCs could be the choice, for now, to sample Ae. niveus mosquitoes. The PCR assay used in MX for nocturnally periodic bancroftian filariasis could be adopted for DspWB. The vector-parasite MX, can be used to evaluate interventions in this area after further standardization of the protocol.

Lymphatic filariasis (LF), caused by nematode parasite–Wuchereria bancrofti, is prevalent in 72 countries with about 1.39 billion people facing the risk of infection. In India LF is endemic in 256 districts. A physiological variant of the parasite, the diurnally sub-periodic Wb (DspWb) is confined to a small pocket of four remotely located isles, in Nicobar district in the Andaman and Nicobar Islands. The parasite is transmitted by a day-biting and forest dwelling mosquito, Aedes niveus. Even after 9 rounds of Mass Drug Administration under the National Programme for LF elimination, microfilaria prevalence was above transmission threshold level (1%), indicating continued transmission. We studied filarial infection in Ae. niveus using molecular xenomonitoring (MX). The vector mosquito was sampled using BioGents Sentinel, Gravid and human baited double bed net-traps. Since the traps did not yield adequate numbers, man landing collections were carried out. The prevalence filarial infection in mosquitoes assessed by molecular assay was above the provisional threshold level (<0.1%.), confirming that the transmission has not been interrupted. MX protocol can further be standardised for use as a surveillance tool in assessing the impact of MDA in this vector-parasite combination.

Elimination of diurnally sub-periodic Wuchereria bancrofti in Andaman and Nicobar Islands, India, using mass DEC-fortified salt as a supplementary intervention to MDA

Feasibility of implementing a DEC-fortified (DEC at 0.2% w/w and iodine) salt strategy to hasten elimination of diurnally sub-periodic Wuchereria bancrofti (DspWB) from the lone foci in Nancowry islands, Nicobar district, India, was assessed. This is a two-arm community-based study: one arm (12 villages, population 2936) received double fortified salt along with annual mass drug administration (MDA) of DEC plus albendazole (DEC-salt+MDA-arm), and another (14 villages; population 4840) received MDA under the National Filaria Elimination Programme. DEC salt was distributed on camp mode supplemented by door delivery. Monthly survey was carried out in fixed and random households to assess the coverage, usage of DEC salt and DEC content. The impact on prevalence of mf at community level and antigenaemia among children was assessed. A total of 21 metric tonnes of free-flow DEC salt manufactured by Tamil Nadu Salt Corporation, India, was distributed for 1 year. In the DEC-salt+MDA-arm, > 90% of the households received and used the DEC salt. DEC was within therapeutic range (0.2-0.32% w/w) in the samples collected from kitchens. Community mf prevalence reduced from 2.27 to 0.14% in the DEC-salt-arm (< 1% in all the villages) and 1.26 to 0.74% (> 1% in 4 out of 14 villages) in the MDA-arm. Ag prevalence reduced to zero from 1.0 (DEC-salt+MDA-arm) and 6.3% (MDA-arm) in 2-3 years old, 1.2 and 3.6% from 2.9 in the DEC-salt-arm and 4.5% in the MDA-arm among 6-7 years old. It was feasible to deliver DEC-fortified salt covering > 90% of the households with compliance reaching the elimination target in the islands.

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

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

Mathematical modelling of lymphatic filariasis elimination programmes in India: required duration of mass drug administration and post-treatment level of infection indicators

Background

India has made great progress towards the elimination of lymphatic filariasis. By 2015, most endemic districts had completed at least five annual rounds of mass drug administration (MDA). The next challenge is to determine when MDA can be stopped. We performed a simulation study with the individual-based model LYMFASIM to help clarify this.

Methods

We used a model-variant for Indian settings. We considered different hypotheses on detectability of antigenaemia (Ag) in relation to underlying adult worm burden, choosing the most likely hypothesis by comparing the model predicted association between community-level microfilaraemia (Mf) and antigenaemia (Ag) prevalence levels to observed data (collated from literature). Next, we estimated how long MDA must be continued in order to achieve elimination in different transmission settings and what Mf and Ag prevalence may still remain 1 year after the last required MDA round. The robustness of key-outcomes was assessed in a sensitivity analysis.

Results

Our model matched observed data qualitatively well when we assumed an Ag detection rate of 50 % for single worm infections, which increases with the number of adult worms (modelled by relating detection to the presence of female worms). The required duration of annual MDA increased with higher baseline endemicity and lower coverage (varying between 2 and 12 rounds), while the remaining residual infection 1 year after the last required treatment declined with transmission intensity. For low and high transmission settings, the median residual infection levels were 1.0 % and 0.4 % (Mf prevalence in the 5+ population), and 3.5 % and 2.0 % (Ag prevalence in 6–7 year-old children).

Conclusion

To achieve elimination in high transmission settings, MDA must be continued longer and infection levels must be reduced to lower levels than in low-endemic communities. Although our simulations were for Indian settings, qualitatively similar patterns are also expected in other areas. This should be taken into account in decision algorithms to define whether MDA can be interrupted. Transmission assessment surveys should ideally be targeted to communities with the highest pre-control transmission levels, to minimize the risk of programme failure.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1768-y) contains supplementary material, which is available to authorized users.

An In Vitro/In Vivo Model to Analyze the Effects of Flubendazole Exposure on Adult Female Brugia malayi

Current control strategies for onchocerciasis and lymphatic filariasis (LF) rely on prolonged yearly or twice-yearly mass administration of microfilaricidal drugs. Prospects for near-term elimination or eradication of these diseases would be improved by availability of a macrofilaricide that is highly effective in a short regimen. Flubendazole (FLBZ), a benzimidazole anthelmintic registered for control of human gastrointestinal nematode infections, is a potential candidate for this role. FLBZ has profound and potent macrofilaricidal effects in many experimental animal models of filariases and in one human trial for onchocerciasis after parental administration. Unfortunately, the marketed formulation of FLBZ provides very limited oral bioavailability and parenteral administration is required for macrofilaricidal efficacy. A new formulation that provided sufficient oral bioavailability could advance FLBZ as an effective treatment for onchocerciasis and LF. Short-term in vitro culture experiments in adult filariae have shown that FLBZ damages tissues required for reproduction and survival at pharmacologically relevant concentrations. The current study characterized the long-term effects of FLBZ on adult Brugia malayi by maintaining parasites in jirds for up to eight weeks following brief drug exposure (6–24 hr) to pharmacologically relevant concentrations (100 nM—10 μM) in culture. Morphological damage following exposure to FLBZ was observed prominently in developing embryos and was accompanied by a decrease in microfilarial output at 4 weeks post-exposure. Although FLBZ exposure clearly damaged the parasites, exposed worms recovered and were viable 8 weeks after treatment.

Onchocerciasis and lymphatic filariasis are debilitating diseases caused by infections with filarial nematodes. The World Health Organization aims to eliminate these infections as public health problems. Despite prolonged control efforts, including chemotherapy through mass drug administration (MDA), transmission and infections persist. Addition of a microfilaricide that is efficacious in a short regimen would enhance prospects for achieving elimination goals. We investigated the long-term effects of the macrofilaricidal drug, flubendazole (FLBZ), on Brugia malayi. Adult parasites were exposed in culture to FLBZ at pharmacologically relevant concentrations (100 nM—10 μM) for up to 24 hr prior to implantation into the abdominal cavity of a jird for long-term maintenance. The greatest drug effect was on embryogenesis; morphological damage was most evident in early developmental stages. There was also a decrease in the release of microfilaria (mf) from the adult. Interestingly, no damage was observed to fully formed mf. Although further studies are required to determine to what extent these findings can be extrapolated to a field setting, an exposure profile which may produce similar effects in vivo has been defined.

Diurnally subperiodic filariasis among the Nicobarese of Nicobar district - epidemiology, vector dynamics & prospects of elimination

In India diurnally subperiodic filariasis (DspWB) is prevalent only in the Nicobar district of Andaman and Nicobar Islands. Studies undertaken at different points of time indicate that this form of filariasis is restricted to a small region in Nancowry group of islands where it is transmitted by mosquito Downsiomyia nivea, a day biting mosquito. Studies on prevalence, distribution, and assessment of endemicity status, vector incrimination, bioecology, host seeking behaviour, population dynamics of the vector, transmission dynamics and clinical epidemiology indicate the prevalence and persistence of this infection in the Nancowry group of islands with perennial transmission. There was no control programme in these islands, until the National programme to eliminate filariasis was launched in 2004. Eight rounds of annual mass drug administration (MDA) with diethyl carbamazine (DEC) + albendazole have been completed. Despite this, microfilaria prevalence remains at above one per cent, the level identified for initiating transmission assessment survey to decide on continuation of MDA further. This necessitates adjunct measures to the ongoing MDA programme in these islands. The vector control options could be an adjunct measure, but the vector is a forest dweller with a unique bio-ecology, therefore, not a technically feasible option. Use of DEC fortified salt for six months to one year could hasten the process of elimination. Although administration of DEC-fortified salt is simple, rapid, safe, and cost-effective, challenges are to be tackled for evolving operationally realistic strategy. Such a strategy requires commitment of all sections of the society, a distribution mechanism that ensures the use of DEC-fortified salt in the Nancowry islands. Here we discuss the plan of action to serve the indigenous communities and operationalizing DEC fortified salt strategy through an inter-sectoral approach involving multiple stakeholders.