Progress to Elimination
WHO lists the milestones towards validation of elimination as:
- Stop the spread of infection through mass drug administration
- Implement MDA in all endemic areas (100% geographical coverage)
- Reduce infection below a threshold at which transmission is not sustainable in all endemic areas and stop MDA
- Demonstrate sustained reduction of infection below the threshold no earlier than 4 years after stopping MDA
- Alleviate suffering by managing morbidity and preventing disability (MMDP)
- Define burden of disease (estimates of the number of patients)
- Recommended minimum package of care available in all areas of known patients (100% geographical coverage)
Progress and achievements in 2018 reported in the latest WHO Weekly Epidemiological Report are substantial . Before establishment of the Global Programme to Eliminate Lymphatic Filariasis (GPELF), LF was responsible for an estimated 5.25 million disability-adjusted life-years (DALYs) and an annual economic loss of at least US$ 5.7 billion per year.1 WHO recommends feasible, cost-effective approaches to put an end to one of the world’s leading causes of avoidable disability.2, 3 After 16 years of the GPELF, LF was considered responsible for at least 1.3 million DALYs, representing a substantial effect of interventions, although the remaining burden is considerable.4
Validation of elimination as a public health problem
For elimination of LF as a public health problem, the prevalence of infection in an area must be reduced to below the target threshold for at least 4 years after MDA and the recommended package of care is provided in all areas in which there are patients with lymphoedema or hydrocoele. In 2018, WHO recognized that Palau, Viet Nam and the Territory of the Wallis and Futuna Islands (France) had met the criteria for elimination of LF as a public health problem.
Referring to the 2019 WHO Weekly Epidemiological Report Tables and Figure will provide further detailed data
Scaling-up mass drug administration
Table 1 of the WHO Weekly Epidemiological Report lists the status of each LF-endemic country according to its progress in conducting MDA and towards validation. In 2018, 49 countries were considered to require MDA. To meet elimination targets, MDA must be delivered consecutively each year in every endemic IU, with at least effective coverage of the total population. MDA had yet to be implemented in all the endemic IUs in 14 countries (columns 1 and 2); 3 countries had not started MDA. Of the 49 countries that required MDA, 35 had reached all endemic IUs with at least one round of MDA in 2018 or previously (column 3 plus Cameroon). MDA was no longer required in the 24 countries in which surveillance is required to ensure that the levels of infection remain below the elimination thresholds; the countries are either in the post-MDA phase but have not met the criteria for validation (column 4) or have been validated as having eliminated LF as a public health problem (column 5).
MDA data by country are reported in Table 2. The cumulative number of treatments given during MDA since 2000 now exceeds 7.7 billion, delivered to >910 million people at least once. In 2018, the population that required MDA was 892.9 million, and 36 countries reported having treated 556.6 million people (62.3%). MDA was not implemented in 6 countries in which it was required. Reports from 5 countries are still awaited, and updates will be posted on the Global Health Observatory preventive chemotherapy portal.7 National programmes planned to treat 697 million people by MDA during 2018, 94 million more than in 2017. According to reports for 2018, effective coverage was achieved in 90% of IUs that conducted MDA. This represents an increase over previous years, but still falls short of the goal of effective coverage in 100% of IUs with each round of MDA. The global treatment gap is now 336.3 million people, who comprise those ineligible for treatment, those missed during MDA, people who were not compliant and those living in endemic IUs where MDA is required but was not delivered (196 million). In 2018, an estimated 31.6 million preschool-aged children (2–4 years) and 152.7 million school-aged children (5–14 years) were treated during LF MDA.
Population requiring MDA and transmission assessment surveys
The number of people requiring interventions for neglected tropical diseases (NTDs) is defined as the NTD indicator of progress towards achieving Sustainable Development Goal (SDG) 3.3.8 In GPELF, the population at risk and requiring MDA is considered to be the total population in all IUs with current evidence of LF endemicity. Based on reports through 2018, 597.1 million people no longer require MDA, representing a 42% reduction from the total population living in IUs that were considered endemic in 2010.
The population in an IU is considered to no longer require MDA once the criteria have been met in both sentinel and spot-check surveys and TAS. Figure 1 shows the cumulative proportion of known endemic IUs by region that have completed TAS and no longer require MDA. A TAS is considered “passed” when the number of children who test positive for LF infection is below the allowed critical cut-off value, which represents the prevalence below which transmission is considered unsustainable. In 2018, TAS were expected in 25 countries. Reports from 19 countries indicate that TAS were conducted in 266 evaluation units (EUs) covering 397 IUs (143 IUs in TAS1, 171 in TAS2 and 83 in TAS3). In 4 countries, the number of infected children exceeded the critical cut off value in at least 1 EU, indicating ongoing transmission after MDA. A repeat TAS1 was required in 2 countries, and 6 of 6 EUs surveyed passed. In 2018, 94.6% (88 of 93) of EUs passed a TAS1, 92.5% (111 of 120) EUs passed TAS2, and all (53 of 53) EUs undergoing TAS3 passed.
- Mathew CG, et al. The health and economic burden of lymphatic filariasis prior to mass drug administration programmes. Clin Infect Dis. 2019;doi:10.1093/cid/ciz671.
- Stillwaggon E, et al. Economic costs and benefits of a community-based lymphedema management program for lymphatic filariasis in Odisha State, India. Am J Trop Med Hyg. 2016;95(4):877–884.
- Turner HC, et al. Investment success in public health: an analysis of the cost-effectiveness and cost-benefit of the global programme to eliminate lymphatic filariasis. Clin Infect Dis. 2017;64(6):728–735.
- Global burden of disease 2017. Seattle (WA): Institute for Health Metrics and Evaluation; 2017.
- Alternative mass drug administration regimens to eliminate lymphatic filariasis. Geneva: World Health Organization; 2017 https://www.who.int/lymphatic_filariasis/resources/9789241550161/en/
- Monitoring and epidemiological assessment of mass drug administration for eliminating lymphatic filariasis: a manual for national elimination programmes. Geneva: World Health Organization, 2011 accessed October 2018
- Preventive chemotherapy data portal. Geneva: World Health Organization; 2017 http://apps.who.int/gho/cabinet/pc.jsp accessed October 2018).
- Global indicator framework for the Sustainable Development Goals and targets of the 2030 agenda for sustainable development. New York City (NY): United Nations (A/RES/71/313) (https://unstats.un.org/sdgs/indicators/indicators-list/, accessed October 2018).
See WHO Weekly Epidemiological Report for the full detailed report