The roadmap towards elimination of lymphatic filariasis by 2030: insights from quantitative and mathematical modelling

Factors influencing implementation of mass drug administration for lymphatic filariasis elimination: a mixed-method study in Odisha, India

Background: Lymphatic filariasis (LF) persists as a public health problem in India. Despite more than ten rounds of mass drug administration (MDA), LF continues to be endemic in the Dhenkanal district of Odisha. Hence, we assessed the coverage and compliance of the MDA program and explored the factors affecting it in the Dhenkanal district. Methods: An explanatory mixed-method study was conducted, wherein for the quantitative survey, 552 participants aged 2 years and above were recruited following a multistage cluster random sampling during February 2022. In-depth interviews were conducted among purposively selected key stakeholders and program implementers. Descriptive statistics were used to report coverage and compliance, along with a 95% confidence interval. Qualitative data were analyzed using a thematic approach. Results: We observed coverage of 99.28% and compliance of 85.87% for MDA drugs. Supervised drug administration proved to be a major pillar in increasing compliance. There was difficulty in administering drugs in urban areas due to gated societies, the absence of individuals during the day, and the perspective toward healthcare providers. Participants reported a lack of confidence in drug distributors and a fear of side effects as major causes for non-compliance. Conclusion: There is a need to strengthen MDA, especially in urban areas. An urban-specific strategy, along with surveillance, behavioral change communication, and the involvement of multi-disciplinary teams, is required.

Lymphatic filariases and soil-transmitted helminthiases in Sri Lanka: the challenge of eliminating residual pockets of transmission

Sri Lanka has successfully met the challenge of controlling both lymphatic filariasis (LF) and soil-transmitted helminthiases (STH) as public health problems. The primary public health strategy for combatting both conditions has been preventive chemotherapy. The national programme for the elimination of LF implemented five annual rounds of mass chemotherapy in the endemic districts from 2002 to 2006 using a combination of diethylcarbamazine and albendazole. The overall microfilaria rate declined from 0.21% in 2001 before the mass chemotherapy, to 0.06% in 2016, at declaration of elimination of LF as a public health problem by the World Health Organization. Currently Sri Lanka is in the phase of post-validation surveillance. Achieving control of STH has been more difficult. Mass deworming programmes have been implemented for nearly a century, and national-level surveys reported prevalence rates declining from 6.9% in 2003 to 1% in 2017. However, neither of these infections has been completely eliminated. A situation analysis indicates continued transmission of both among high-risk communities. This paper explores the reasons for persistence of transmission of both LF and STH in residual pockets and the measures that are required to achieve long-term control, or perhaps even interrupt transmission in Sri Lanka. This article is part of the theme issue 'Challenges and opportunities in the fight against neglected tropical diseases: a decade from the London Declaration on NTDs'.

Coverage evaluation of mass drug administration with triple drug regimen in an evaluation unit in Nagpur district of Maharashtra, India

BACKGROUND

Triple drug regimen (IDA; Ivermectin, Diethylcarbamazine, Albendazole) recommended for accelerating elimination of lymphatic filariasis was launched in India in December 2018. Nagpur district in Maharashtra was one of the first five districts where this strategy was introduced. The National Vector Borne Disease Control Programme (NVBDCP) at the district reported ~85.0% treatment coverage in the first round of mass drug administration (MDA) with IDA implemented in EU-2 in Nagpur district in January 2019. As per the national guideline, a coverage evaluation survey was carried out and both quantitative and qualitative data were collected to assess the treatment coverage, the level of community preparation and identify the gaps, if any, for improvement.

METHODOLOGY

A Coverage Evaluation Survey (CES) following the WHO recommended protocol was conducted in one of the two evaluation units (EU-2) in Nagpur district in March 2019. Coverage Sample Builder (CSB) V2.9 tool was used to calculate the sample size, select sites and estimate drug coverage. The CSB tool followed a two-stage cluster sampling procedure to select 30 primary sampling units (ward/village as a cluster) and a list of random numbers for selecting households (HHs) in each cluster. The results were analyzed for operational indicators. Stata ver. 14.0 software was used to construct the 95% confidence limits accounting for clustering.

RESULTS

A total of 1601 individuals aged 5-85 years of both gender from 328 HHs were surveyed from the 30 randomly selected clusters in EU-2. The mean age was 33.8±17.6 years. Among the surveyed population, 78.0% received the drugs (programme reach) and 66.1% consumed the drugs (survey coverage). Survey coverage was significantly higher in rural (82.6%) than in urban (59.4%) and peri-urban (58.6%) areas (P<0.001). Directly observed treatment (DOT) among the surveyed population was 51.6%. Adverse events were reported among 6.9% respondents who reported to have consumed the drugs.

CONCLUSION

The IDA based MDA strategy could achieve just the required level of treatment coverage (~65%) in EU-2, Nagpur district, which had previously undergone several rounds of DA-MDAs (Diethylcarbamazine, Albendazole). Having achieved an effective treatment coverage of >80% in rural areas, the coverage in urban and peri-urban areas need to be improved in order to attain the impact of IDA-MDA. It is imperative to strengthen drug delivery and community preparation activities along with improved DOT especially in urban and peri-urban areas to achieve the required level of treatment coverage. Addition of ivermectin did not have any additional perceived adverse events.

Population pharmacokinetic model of ivermectin in mass drug administration against lymphatic filariasis

BACKGROUND

Ivermectin (IVM) is a broad-spectrum anthelmintic drug used to treat diseases caused by filarial worms, such as onchocerciasis and lymphatic filariasis (LF). IVM is part of a triple-drug therapy used by the Mass Drug Administration (MDA) as a preventive strategy to eradicate LF in sub-Saharan Africa. The drug shows high variability in drug exposure in previous pharmacokinetic studies. This study aims to build a population pharmacokinetic (PopPK) model to identify and quantify the possible sources of the variability of IVM exposure after a single-oral dose in LF-infected subjects and healthy individuals.

METHODOLOGY / PRINCIPAL FINDINGS

In this analysis, 724 samples were collected from treatment-naïve Wuchereria bancrofti-infected (n = 32) and uninfected (n = 24) adults living in Côte d'Ivoire who had received one dose of IVM as a part of triple-drug therapy. PopPK analysis was conducted using Phoenix NLME 8.3 software. The Monte Carlo simulation based on the final model was performed to simulate drug exposure among different dosing groups (200 μg/kg, 18 mg, and 36 mg). A two-compartment model with zero-order dose input into the absorption compartment with a lag time function followed by first-order absorption and linear elimination best described the IVM's pharmacokinetic (PK) parameters. The final model identifies that the PK parameters of IVM are not affected by LF infection. Sex was a significant covariate on the peripheral volume of distribution (Vp/F, 53% lower in men than in women). IVM drug exposure shows linear pharmacokinetic behavior among the simulated dosing groups with similar drug exposure based on sex.

CONCLUSION/SIGNIFICANCE

We have developed a PopPk model to describe and identify possible sources of the variability of IVM exposure. To our knowledge, this is the first PopPK study of IVM in patients with LF.

TRIAL REGISTRATION

NCT02845713; NCT03664063.

Risk Factors of Noncompliance to Preventive Mass Drug Administration for Eliminating Lymphatic Filariasis: A Case-Control Study in Jawi District, Northwest Ethiopia

Background. High compliance is crucial for the success of a mass drug administration program to achieve lymphatic filariasis elimination. However, the presence of persistently noncompliant individuals might delay the elimination target. Besides, although context-based research is essential to designing effective strategies, only a few studies have focused on identifying factors that play a role in noncompliance with mass drug administration in Africa. Therefore, this study was conducted to identify the factors associated with noncompliance to prevent mass drug administration using ivermectin-with-albendazole for the elimination of lymphatic filariasis in Northwest Ethiopia. Methods. A case-control study was conducted in Jawi District, Northwest Ethiopia. All individuals who are permanently living in the study area and registered on the annual chemotherapy registration book since 2015 were included in this study. A two-proportion formula was used to estimate the required sample size and 348 cases and 348 controls were selected by identification number on the village chemotherapy registration book using a systematic sampling technique. Data were collected by face-to-face interviews using a structured questionnaire developed through an intensive literature review. Then, data were entered and cleaned by using the EPI DATA software, and analyses were conducted using SPSS version 26. Finally, a logistic regression analysis technique was applied to identify the risk factors using adjusted odds ratio as measures of effect. Results. A total of 690 (99.1%) participants, 345 cases and 345 controls, were included in the study. Younger age (AOR = 1.60; 95%CI: 1.10, 2.33), female sex (AOR = 1.56; 95%CI: 1.24, 3.93), thought of not being susceptible to the disease (AOR = 2.36, 95%CI: 1.80, 4.32), lack of disease knowledge (AOR = 1.88; 95% CI: 1.38, 3.81), fear of drug side effect (AOR = 2.45; 95% CI:1.23, 4.86), and not participating in community drug distributors selection (AOR = 2.58; 95% CI: 1.70, 3.91) were found to be the risk factors significantly associated with noncompliance. Conclusion. Noncompliance with lymphatic filariasis mass drug administration therapy was associated with specific demographic, individual, program, and drug delivery characteristics. This finding has important implications for program effectiveness and would be used to accelerate the elimination of lymphatic filariasis in the study area and other endemic settings.

Occurrence of Lymphatic Filariasis infection after 15 years of mass drug administration in two hotspot districts in the Upper East Region of Ghana

Background

Lymphatic filariasis (LF) causes chronic morbidity, which usually manifests as lymphedema or hydrocele. Mass drug administration (MDA) began in Kassena Nankana East Municipal (KNEM) and Nabdam, two hotspot districts in the Upper East Region in Ghana, in 2000 and 2005, respectively. This cross-sectional study evaluated the impact of 15 years of MDA on the control of LF as determined by circulating filarial antigen (CFA) and microfilariae assessment in the KNEM and the Nabdam districts.

Methodology/Principal findings

A total of 7,453 participants from eight sub-districts in the two hotspot districts (KNEM: N = 4604; Nabdam: N = 2849) were recruited into the study. The overall CFA prevalence as determined by the FTS was 19.6% and 12.8% in the KNEM and Nabdam districts, respectively. Manyoro, a sub-district on the border with Burkina Faso, recorded the highest CFA prevalence of 26% in the KNEM. Assessment of microfilariae and Og4C3 antigen was done from 1009 (KNEM: N = 799 (79.2%); Nabdam: N = 210 (20.8%)) randomly selected FTS-positive (N = 885) and FTS-negative (N = 124) individuals. The Og4C3 antigen was found in 22.6%/23.0% of the selected individuals (KNEM/Nabdam), whereas the night blood revealed microfilariae in only 0.7%/0.5%.

Conclusions/Significance

Using the WHO endorsed FTS, CFA prevalence exceeded the long-standing <2% threshold—which may need revision and validation. Surprisingly, the Og4C3 ELISA showed positive results in only about one-fifth of the FTS positive samples. However, even this result would not have met the <2% CFA criteria for LF elimination. In contrast, projections from the microfilariae results revealed a halt in LF transmission. The global elimination target was due in 2020 but has been extended to 2030 since this could not be met. Focused MDA intervention intensification on seasonal migrants and non-compliers, and implementation of alternative treatment strategies may suffice for the elimination of the disease.

Lymphatic filariasis (LF) is a major neglected tropical disease (NTD) affecting over 120 million individuals worldwide and identified as one of WHO’s 20 NTDs targeted for elimination. It has strong links with poverty and is associated with significant clinical morbidity, which impose considerable socio-psychological and economic burdens on the affected individuals. One of the main goals of the Global Programme to Eliminate Lymphatic Filariasis (GPELF) is the use of mass drug administration (MDA) to interrupt LF transmission. The initial 2020 elimination target year set by the GPELF could not be met, with 2030 now the new proposed year targeted for global elimination. The study evaluated the impact of 15 years of MDA on the control of LF in two hotspot districts in Ghana. The results from this study are indicative of a halt in LF transmission in the districts, with microfilaria detected in <1% of those sampled. However, the antigenemia prevalence is still above the recommended level. MDA should be intensified especially at the border towns or alternative treatment strategies should be employed to finally eliminate the disease as some people who are still with the active infection can serve as a reservoir for recrudescence and transmission in already “LF-free” areas.

A mouse infection model and long-term lymphatic endothelium co-culture system to evaluate drugs against adult Brugia malayi

The development of new drugs targeting adult-stage lymphatic filarial nematodes is hindered by the lack of a robust long-term in vitro culture model. Testing potential direct-acting and anti-Wolbachia therapeutic candidates against adult lymphatic filariae in vitro requires their propagation via chronic infection of gerbils. We evaluated Brugia malayi parasite burden data from male Mongolian gerbils compared with two immune-deficient mouse strains highly susceptible to B. malayi: CB.17 Severe-Combined Immmuno-Deficient (SCID) and interleukin-4 receptor alpha, interleukin-5 double knockout (IL-4Rα-/-IL-5-/-) mice. Adult worms generated in IL-4Rα-/-IL-5-/- mice were tested with different feeder cells (human embryonic kidney cells, human adult dermal lymphatic endothelial cells and human THP-1 monocyte differentiated macrophages) and comparative cell-free conditions to optimise and validate a long-term in vitro culture system. Cultured parasites were compared against those isolated from mice using motility scoring, metabolic viability assay (MTT), ex vivo microfilariae release assay and Wolbachia content by qPCR. A selected culture system was validated as a drug screen using reference anti-Wolbachia (doxycycline, ABBV-4083 / flubentylosin) or direct-acting compounds (flubendazole, suramin). BALB/c IL-4Rα-/-IL-5-/- or CB.17 SCID mice were superior to Mongolian gerbils in generating adult worms and supporting in vivo persistence for periods of up to 52 weeks. Adult females retrieved from BALB/c IL-4Rα-/-IL-5-/- mice could be cultured for up to 21 days in the presence of a lymphatic endothelial cell co-culture system with comparable motility, metabolic activity and Wolbachia titres to those maintained in vivo. Drug studies confirmed significant Wolbachia depletions or direct macrofilaricidal activities could be discerned when female B. malayi were cultured for 14 days. We therefore demonstrate a novel methodology to generate adult B. malayi in vivo and accurately evaluate drug efficacy ex vivo which may be adopted for drug screening with the dual benefit of reducing overall animal use and improving anti-filarial drug development.

Pyrvinium Pamoate and Structural Analogs Are Early Macrofilaricide Leads

Onchocerciasis and lymphatic filariasis are neglected tropical diseases caused by infection with filarial worms. Annual or biannual mass drug administration with microfilaricidal drugs that kill the microfilarial stages of the parasites has helped reduce infection rates and thus prevent transmission of both infections. However, success depends on high population coverage that is maintained for the duration of the adult worm's lifespan. Given that these filarial worms can live up to 14 years in their human hosts, a macrofilaricidal drug would vastly accelerate elimination efforts. Here, we have evaluated the repurposed drug pyrvinium pamoate as well as newly synthesized analogs of pyrvinium for their efficacy against filarial worms in vitro and in vivo. We found that pyrvinium pamoate, tetrahydropyrvinium and one of the analogs were highly potent in inhibiting worms in in vitro whole-worm screening assays, and that all three compounds reduced female worm fecundity and inhibited embryogenesis in the Brugia pahangi-gerbil in vivo model of infection.

Evaluating the Diagnostic Test Accuracy of Molecular Xenomonitoring Methods for Characterizing Community Burden of Lymphatic Filariasis

Background

Molecular xenomonitoring (MX), the detection of pathogen DNA in mosquitoes, is a recommended approach to support lymphatic filariasis (LF) elimination efforts. Potential roles of MX include detecting presence of LF in communities and quantifying progress towards elimination of the disease. However, the relationship between MX results and human prevalence is poorly understood.

Methods

We conducted a systematic review and meta-analysis from all previously conducted studies that reported the prevalence of filarial DNA in wild-caught mosquitoes (MX rate) and the corresponding prevalence of microfilaria (mf) in humans. We calculated a pooled estimate of MX sensitivity for detecting positive communities at a range of mf prevalence values and mosquito sample sizes. We conducted a linear regression to evaluate the relationship between mf prevalence and MX rate.

Results

We identified 24 studies comprising 144 study communities. MX had an overall sensitivity of 98.3% (95% confidence interval, 41.5–99.9%) and identified 28 positive communities that were negative in the mf survey. Low sensitivity in some studies was attributed to small mosquito sample sizes (<1000) and very low mf prevalence (<0.25%). Human mf prevalence and mass drug administration status accounted for approximately half of the variation in MX rate (R² = 0.49, P < .001). Data from longitudinal studies showed that, within a given study area, there is a strong linear relationship between MX rate and mf prevalence (R² = 0.78, P < .001).

Conclusions

MX shows clear potential as tool for detecting communities where LF is present and as a predictor of human mf prevalence.

Supporting drug development for neglected tropical diseases using mathematical modelling

Drug-based interventions are at the heart of global efforts to reach elimination as a public health problem (trachoma, soil-transmitted helminthiases, schistosomiasis, lymphatic filariasis) or elimination of transmission (onchocerciasis) for 5 of the most prevalent neglected tropical diseases tackled via the World Health Organization preventive chemotherapy strategy. While for some of these diseases there is optimism that currently available drugs will be sufficient to achieve the proposed elimination goals, for others—particularly onchocerciasis—there is a growing consensus that novel therapeutic options will be needed. Since in this area no high return of investment is possible, minimizing wasted money and resources is essential. Here, we use illustrative results to show how mathematical modeling can guide the drug development pathway, yielding resource-saving and efficiency payoffs, from the refinement of target product profiles and intended context of use to the design of clinical trials.

An Integrated Approach to Identify New Anti-Filarial Leads to Treat River Blindness, a Neglected Tropical Disease

Filarial worms cause multiple debilitating diseases in millions of people worldwide, including river blindness. Currently available drugs reduce transmission by killing larvae (microfilariae), but there are no effective cures targeting the adult parasites (macrofilaricides) which survive and reproduce in the host for very long periods. To identify effective macrofilaricides, we carried out phenotypic screening of a library of 2121 approved drugs for clinical use against adult Brugia pahangi and prioritized the hits for further studies by integrating those results with a computational prioritization of drugs and associated targets. This resulted in the identification of 18 hits with anti-macrofilaricidal activity, of which two classes, azoles and aspartic protease inhibitors, were further expanded upon. Follow up screening against Onchocerca spp. (adult Onchocerca ochengi and pre-adult O. volvulus) confirmed activity for 13 drugs (the majority having IC50 < 10 μM), and a counter screen of a subset against L. loa microfilariae showed the potential to identify selective drugs that prevent adverse events when co-infected individuals are treated. Stage specific activity was also observed. Many of these drugs are amenable to structural optimization, and also have known canonical targets, making them promising candidates for further optimization that can lead to identifying and characterizing novel anti-macrofilarial drugs.

How modelling can help steer the course set by the World Health Organization 2021-2030 roadmap on neglected tropical diseases

The World Health Organization recently launched its 2021-2030 roadmap, Ending the Neglect to Attain the Sustainable Development Goals , an updated call to arms to end the suffering caused by neglected tropical diseases. Modelling and quantitative analyses played a significant role in forming these latest goals. In this collection, we discuss the insights, the resulting recommendations and identified challenges of public health modelling for 13 of the target diseases: Chagas disease, dengue, gambiense human African trypanosomiasis (gHAT), lymphatic filariasis (LF), onchocerciasis, rabies, scabies, schistosomiasis, soil-transmitted helminthiases (STH), Taenia solium taeniasis/ cysticercosis, trachoma, visceral leishmaniasis (VL) and yaws. This piece reflects the three cross-cutting themes identified across the collection, regarding the contribution that modelling can make to timelines, programme design, drug development and clinical trials.

How modelling can help steer the course set by the World Health Organization 2021-2030 roadmap on neglected tropical diseases

The World Health Organization recently launched its 2021-2030 roadmap, Ending the Neglect to Attain the Sustainable Development Goals , an updated call to arms to end the suffering caused by neglected tropical diseases. Modelling and quantitative analyses played a significant role in forming these latest goals. In this collection, we discuss the insights, the resulting recommendations and identified challenges of public health modelling for 13 of the target diseases: Chagas disease, dengue, gambiense human African trypanosomiasis (gHAT), lymphatic filariasis (LF), onchocerciasis, rabies, scabies, schistosomiasis, soil-transmitted helminthiases (STH), Taenia solium taeniasis/ cysticercosis, trachoma, visceral leishmaniasis (VL) and yaws. This piece reflects the three cross-cutting themes identified across the collection, regarding the contribution that modelling can make to timelines, programme design, drug development and clinical trials.

The endosymbiont Wolbachia rebounds following antibiotic treatment

Antibiotic treatment has emerged as a promising strategy to sterilize and kill filarial nematodes due to their dependence on their endosymbiotic bacteria, Wolbachia. Several studies have shown that novel and FDA-approved antibiotics are efficacious at depleting the filarial nematodes of their endosymbiont, thus reducing female fecundity. However, it remains unclear if antibiotics can permanently deplete Wolbachia and cause sterility for the lifespan of the adult worms. Concerns about resistance arising from mass drug administration necessitate a careful exploration of potential Wolbachia recrudescence. In the present study, we investigated the long-term effects of the FDA-approved antibiotic, rifampicin, in the Brugia pahangi jird model of infection. Initially, rifampicin treatment depleted Wolbachia in adult worms and simultaneously impaired female worm fecundity. However, during an 8-month washout period, Wolbachia titers rebounded and embryogenesis returned to normal. Genome sequence analyses of Wolbachia revealed that despite the population bottleneck and recovery, no genetic changes occurred that could account for the rebound. Clusters of densely packed Wolbachia within the worm's ovarian tissues were observed by confocal microscopy and remained in worms treated with rifampicin, suggesting that they may serve as privileged sites that allow Wolbachia to persist in worms while treated with antibiotic. To our knowledge, these clusters have not been previously described and may be the source of the Wolbachia rebound.