Diagnostics to support elimination of lymphatic filariasis-Development of two target product profiles.

As lymphatic filariasis (LF) programs move closer to established targets for validation elimination of LF as a public health problem, diagnostic tools capable of supporting the needs of the programs are critical for success. Known limitations of existing diagnostic tools make it challenging to have confidence that program endpoints have been achieved. In 2019, the World Health Organization (WHO) established a Diagnostic Technical Advisory Group (DTAG) for Neglected Tropical Diseases tasked with prioritizing diagnostic needs including defining use-cases and target product profiles (TPPs) for needed tools. Subsequently, disease-specific DTAG subgroups, including one focused on LF, were established to develop TPPs and use-case analyses to be used by product developers. Here, we describe the development of two priority TPPs for LF diagnostics needed for making decisions for stopping mass drug administration (MDA) of a triple drug regimen and surveillance. Utilizing the WHO core TPP development process as the framework, the LF subgroup convened to discuss and determine attributes required for each use case. TPPs considered the following parameters: product use, design, performance, product configuration and cost, and access and equity. Version 1.0 TPPs for two use cases were published by WHO on 12 March 2021 within the WHO Global Observatory on Health Research and Development. A common TPP characteristic that emerged in both use cases was the need to identify new biomarkers that would allow for greater precision in program delivery. As LF diagnostic tests are rarely used for individual clinical diagnosis, it became apparent that reliance on population-based surveys for decision making requires consideration of test performance in the context of such surveys. In low prevalence settings, the number of false positive test results may lead to unnecessary continuation or resumption of MDA, thus wasting valuable resources and time. Therefore, highly specific diagnostic tools are paramount when used to measure low thresholds. The TPP process brought to the forefront the importance of linking use case, program platform and diagnostic performance characteristics when defining required criteria for diagnostic tools.

Correction to: How Thailand eliminated lymphatic filariasis as a public health problem.

After publication of this article [1], it was brought to our attention that figure 2 did not display correctly. The correct figure 2 is as below.

How Thailand eliminated lymphatic filariasis as a public health problem.

BACKGROUND: Lymphatic filariasis is endemic in nine of the eleven Member States of the World Health Organization South East Asia Region. This article describes the intensive interventions with the National Programme for Elimination of Lymphatic Filariasis in Thailand since its launch in 2001 till the validation of its elimination in 2017. METHODS: A baseline epidemiological survey was initiated in 2001 to identify both brugian and bancroftian filarial areas and delineate its endemicity. Mass drug administration (MDA) with diethylcarbamazine citrate (DEC) and albendazole (ALB) was implemented in a total of 357 implementation units (IUs) in 11 lymphatic filariasis (LF) endemic provinces. The implementing unit (IU) was a sub-village. Stop-MDA surveys were conducted in 2006 in the 11 LF endemic provinces among population over 6 years of age and children of ≤6 years using immunochromatographic test (ICT) for Wuchereria bancrofti antigen and microfilariae (mf) detection for Brugia malayi. In Narathiwat province, Stop-MDA surveys were done in 2011 using ELISA. Transmission assessment surveys (TAS) were conducted in 2012-2013, 2015 and 2016-2017 among school students in the 6-7-year age-group. Surveillance of migrant populations through the national migrant health checkup were intensified in seven provinces over 2002-2017 for LF antigenaemia using ICT test cards. In four B. malayi endemic provinces, annual surveys to detect LF reservoir in domestic cats commenced in 1994. A 2001 survey of the chronic disease burden for LF established a register of the cumulative number of people with lymphedema/elephantiasis. RESULTS: A total of five rounds of MDA annually were implemented over 2002-2006 in all IUs. Additional annual rounds of MDA were required in 87 IUs of Narathiwat province from 2007 to 2011 due to persistent infection. The annual national drug coverage with MDA over 2002-2012 was in the range of 68.0 to 95.4%. Stop-MDA surveys in 2006 in the 11 LF endemic provinces found nine mf positive cases in seven IUs in Narathiwat province with the highest prevalence of 0.8% (range: 0.1-0.8%). In Narathiwat TAS-1, TAS-2 and TAS-3 detected below transmission threshold rates for B. malayi mf among antibody positive children (0.3, 0.2 and 0.7% respectively). Contact tracing both all mf cases in all three TAS yielded no positive cases. Through the migrant health checkup, a total of 23 477 persons were tested, showing a positive rate of 0.7% (range: 0.1-2.7%) over years 2002-2017. In Narathiwat province, annual ivermectin treatment among cats commenced in 2003 resulting in a decline of mf prevalence among cats from 8.0% in 1995 to 0.8% in 2015. As of April 2017, a total of 99 lymphoedema/elephantiasis patients were registered and followed-up under 34 health facilities. CONCLUSIONS: Thailand over the years 2002 to 2011 conducted extensive MDA with high coverage rates. Through periodic and regular monitoring surveys it delineated LF transmission areas at sub-village level and demonstrated through its evaluation surveys - the Stop-MDA surveys and TAS, below transmission threshold rates that enabled its validation of LF elimination. In September 2017, World Health Organization acknowledged the Ministry of Health Thailand had eliminated lymphatic filariasis as a public health problem.

How elimination of lymphatic filariasis as a public health problem in the Kingdom of Cambodia was achieved.

BACKGROUND: Endemicity of lymphatic filariasis (LF) in Cambodia was proven in 1956 when microfilariae were detected in mosquitos in the Kratié province. In 2001, an extensive study confirmed the presence of both Brugia malayi and Wuchereria bancrofti microfilariae. In 2003, the Ministry of Health established a national task force to develop policies and strategies for controlling and eliminating neglected tropical diseases (NTDs), with the goal of eliminating LF by 2015. This article summarizes the work accomplished to eliminate LF as a public health problem in Cambodia. METHODS: The National Program to Eliminate Lymphatic Filariasis made excellent progress in the goal towards elimination due to strong collaboration between ministries, intensive supervision by national staff, and advocacy for mobilization of internal and external resources. Mass drug administration (MDA) with diethylcarbamazine citrate and albendazole was conducted in six implementation units, achieving > 70% epidemiological coverage for five consecutive rounds, from 2005 to 2009. In 2006, in 14 provinces, healthcare workers developed a line list of lymphedema and hydrocele patients, many of whom were > 40 years old and had been affected by LF for many years. The national program also trained healthcare workers and provincial and district staff in morbidity management and disability prevention, and designated health centers to provide care for lymphedema and acute attack. Two reference hospitals were designated to administer hydrocele surgery. RESULTS: Effectiveness of MDA was proven with transmission assessment surveys. These found that less than 1% of school children had antigenemia in 2010, which fell to 0% in both 2013 and 2015. A separate survey in one province in 2015 using Brugia Rapid tests to test for LF antibody found one child positive among 1677 children. The list of chronic LF patients was most recently updated and confirmed in 2011-2012, with 32 lymphoedema patients and 17 hydrocele patients listed. All lymphedema patients had been trained on self-management and all hydrocele patients had been offered free surgery. CONCLUSIONS: Due to the success of the MDA and the development of health center capacity for patient care, along with benefits gained from socioeconomic improvements and other interventions against vector-borne diseases and NTDs, Cambodia was validated by the World Health Organization as achieving LF elimination as a public health problem in 2016.

Determinants of success in national programs to eliminate lymphatic filariasis: a perspective identifying essential elements and research needs.

The Global Programme to Eliminate Lymphatic Filariasis (GPELF) was launched in 2000. To understand why some national programs have been more successful than others, a panel of individuals with expertise in LF elimination efforts met to assess available data from programs in 8 countries. The goal was to identify: 1) the factors determining success for national LF elimination programs (defined as the rapid, sustained reduction in microfilaremia/antigenemia after repeated mass drug administration [MDA]); 2) the priorities for operational research to enhance LF elimination efforts. Of more than 40 factors identified, the most prominent were 1) initial level of LF endemicity; 2) effectiveness of vector mosquitoes; 3) MDA drug regimen; 4) population compliance. Research important for facilitating program success was identified as either biologic (i.e., [1] quantifying differences in vectorial capacity; [2] identifying seasonal variations affecting LF transmission) or programmatic (i.e., [1] identifying quantitative thresholds, especially the population compliance levels necessary for success, and the antigenemia or microfilaremia prevalence at which MDA programs can stop with minimal risk of resumption of transmission; [2] defining optimal drug distribution strategies and timing; [3] identifying those individuals who are "persistently non-compliant" during MDAs, the reasons for this non-compliance and approaches to overcoming it). While addressing these challenges is important, many key determinants of program success are already clearly understood; operationalizing these as soon as possible will greatly increase the potential for national program success.

Diurnal pattern of human-biting activity and transmission of subperiodic Wuchereria bancrofti (Filariidea: Dipetalonematidae) by Ochlerotatus niveus (Diptera: Culicidae) on the Andaman and Nicobar islands of India.

We monitored diel-landing periodicity (biting activity/cycle) of Ochlerotatus niveus and the infection/infectivity pattern through human-landing collections on Teressa Island, which is remotely located in the Nicobar district of the Andaman and Nicobar group of Islands of India, for a period of one year. The biting activity was seen throughout the day, exhibiting a bimodal peak, the first at dawn (4:00-6:00 AM) and the other towards dusk (5:00-6:00 PM). This pattern was similar during all the seasons of the year. Peak biting hours of Oc. niveus coincides with the peak appearance of microfilariae. Overall infection and infectivity rates were 2.65% and 0.5%, respectively. Perennial transmission is evident from the records of vectors with parasites (infection), including infective larvae in all months of the year, although no infective mosquitoes were recorded at a few points. The risk of transmission of filariasis based on parity status of Oc. niveus was maximal at dusk (5:00-6:00 PM) in this region. The issue of control with respect to reducing human-vector contact is discussed.

Mass drug administration to eliminate lymphatic filariasis in India.

Mass drug administration (MDA) to eliminate lymphatic filariasis is already in place in 32 out of 83 endemic countries. Expansion of the MDA programme to other countries and within large countries such as India is necessary to achieve the goal of lymphatic filariasis elimination. However, expansion and sustenance of the global campaign to eliminate lymphatic filariasis requires commitment and allocation of funds by governments and donor agencies. This could be achieved, at least to some extent, by highlighting the benefits of the programme in relation to costs. On the basis of various studies in south India, this article assesses the costs, effectiveness and economic and social benefits of the MDA programmes aimed at eliminating lymphatic filariasis.