Control and elimination of lymphatic filariasis in Oceania: Prevalence, geographical distribution, mass drug administration, and surveillance in Samoa, 1998-2017.

Lymphatic filariasis (LF) is a major public health problem globally and in the Pacific Region. The Global Programme to Eliminate LF has made great progress but LF is persistent and resurgent in some Pacific countries and territories. Samoa remains endemic for LF despite elimination efforts through multiple two-drug mass drug administrations (MDA) since 1965, including renewed elimination efforts started in 1999 under the Pacific Programme for Elimination of LF (PacELF). Despite eight rounds of national and two rounds of subnational MDA under PacELF, Samoa failed transmission assessment surveys (TAS) in all three evaluation units in 2017. In 2018, Samoa was the first to distribute countrywide triple-drug MDA using ivermectin, diethylcarbamazine (DEC), and albendazole. This paper provides a review of MDAs and historical survey results from 1998 to 2017 in Samoa and highlights lessons learnt from LF elimination efforts, including challenges and potential ways to overcome them to successfully achieve elimination.

Progress in the elimination of lymphatic filariasis in the Western Pacific Region: successes and challenges.

The Western Pacific Region is the largest and most diverse region in the world, made up of 37 countries and territories in the Pacific, Oceania and parts of Asia, with a population of more than 1.9 billion people stretching over an area from China and Mongolia in the north to New Zealand in the south. In 1999, 22 countries and territories in the Pacific joined together and launched the Pacific Programme to Eliminate Lymphatic Filariasis. Shortly after, the Global Programme to Eliminate Lymphatic Filariasis was launched in 2000. In 2004, 12 countries in the Asia subregion of the Western Pacific Region and Southeast Asian Region joined and developed the Mekong-Plus Strategic Plan for Elimination of Lymphatic Filariasis. Since then, significant efforts have been made by all endemic countries, with annual mass drug administration (MDA) as a principal strategy, through strong partnership with the WHO and other donors and partners. As a result, by the end of 2019, 10 of 22 endemic countries in the region, including 8 of 16 countries in the Pacific and 2 countries in the Asia subregion, achieved WHO validation for elimination of lymphatic filariasis (LF) as a public health problem. All the other countries are either progressing with post-MDA surveillance or accelerating efforts by adoption of the new triple drug therapy strategy and enhancement of MDA campaigns to tackle persistent transmission. Some 85% of the originally endemic implementation units have stopped MDA and the number of people requiring MDA for LF in the Western Pacific Region was reduced by 72% from 2000 to 2018. This paper reviews the progress, key success factors and remaining challenges and indicates the way forward to achieve LF elimination in the Western Pacific Region.

Lymphatic filariasis in Fiji: progress towards elimination, 1997-2007.

BACKGROUND: Lymphatic filariasis (LF) is a major public health problem in the Pacific Region, including in Fiji. Through transmission by the mosquito vector Aedes, Fiji has suffered the burden of remaining endemic with LF despite efforts at elimination prior to 1999. In the year 1999, Fiji agreed to take part in the Pacific Programme for Elimination of LF (PacELF) and the Global Programme to Eliminate LF. METHODS: This study reviewed and collated past data on LF in Fiji between 1997 and 2007. Sources included published papers as well as unpublished PacELF and WHO program meeting and survey reports. Records were held at Fiji's Department of Health and Medical Services, James Cook University and the WHO office in Suva, Fiji. RESULTS: Baseline surveys between 1997 and 2002 showed that Fiji was highly endemic for LF with an estimated 16.6% of the population antigen positive and 6.3% microfilaria positive at that time. Five rounds of annual mass drug administration (MDA) using albendazole and diethylcarbamazine commenced in 2002. Programmatic coverage reported was 58-70% per year, but an independent coverage survey in 2006 in Northern Division after the fifth MDA suggested that actual coverage may have been higher. Monitoring of the program consisted of antigen prevalence surveys in all ages with sentinel and spot check surveys carried out in 2002 (pre MDA), 2004, and 2005, together with knowledge, attitude, and practice surveys. The stop-MDA survey (C survey) in 2007 was a nationwide stratified cluster survey of all ages according to PacELF guidelines, designed to sample by administrative division to identify areas still needing MDA. The national antigen prevalence in 2007 was reduced by more than a third to 9.5%, ranging from 0.9% in Western Division to 15.4% in Eastern Division, while microfilaria prevalence was reduced by almost four-fifths to 1.4%. Having not reached the target threshold of 1% prevalence in all ages, Fiji wisely decided to continue MDA after 2007 but to move from nationwide implementation to four (later five) separate evaluation units with independent timelines using global guidelines, building on program experience to put more emphasis on increasing coverage through prioritized communication strategies, community participation, and morbidity alleviation. CONCLUSION: Fiji conducted nationwide MDA for LF annually between 2002 and 2006, monitored by extensive surveys of prevalence, knowledge, and coverage. From a high baseline prevalence in all divisions, large reductions in overall and age-specific prevalence were achieved, especially in the prevalence of microfilariae, but the threshold for stopping MDA was not reached. Fiji has a large rural and geographically widespread population, program management was not consistent over this period, and coverage achieved was likely not optimal in all areas. After learning from these many challenges and activities, Fiji was able to build on the progress achieved and the heterogeneity observed in prevalence to realign towards a more stratified and improved program after 2007. The information presented here will assist the country to progress towards validating elimination in subsequent years.

Elimination of lymphatic filariasis as a public health problem in Niue under PacELF, 1999-2016.

BACKGROUND: Lymphatic filariasis (LF) is a mosquito-borne parasitic disease which is targeted for elimination as a public health problem worldwide. Niue is a small self-governing South Pacific island nation with approximately 1600 residents that was formerly LF endemic. Here, we review the progress made towards eliminating LF in Niue since 1999. METHODS: This study has reviewed all the available literature relating to LF in Niue to assess surveillance efforts and the elimination of transmission. Reviewed documentation included both published and unpublished works including historical reports of LF, WHO PacELF records, and Niue Country Reports of the national LF elimination program. FINDINGS: Niue conducted mapping of baseline LF endemicity by testing the total present and consenting population for LF antigen with immunochromatographic test (ICT) in 1999, when circulating filarial antigen prevalence was 3.1% (n = 1794). Five nationwide annual mass drug administration (MDA) rounds with albendazole (400 mg) and diethylcarbamazine citrate (DEC) were undertaken from 2000 to 2004, with coverage reported from distribution records ranging from 78 to 99% of the eligible population, which excluded pregnant women and children under 2 years of age. A further whole population survey using ICT in 2001 found 1.3% positive (n = 1630). In 2004, antigen prevalence had reduced to 0.2% (n = 1285). A similar post-MDA survey in 2009 indicated antigen prevalence to be 0.5% (n = 1378). Seven positive cases were re-tested and re-treated every six months until negative. CONCLUSIONS: After five rounds of MDA, Niue had reduced the LF antigen population prevalence in all ages from 3.1% to below 1% and maintained this prevalence for a further five years. Due to Niue's small population, surveillance was done by whole population surveys. Niue's results support the WHO recommended strategy that five to six rounds of annual MDA with effective population coverage can successfully interrupt the transmission of LF. Niue received official acknowledgement of the validation of elimination of LF as a public health problem by the WHO Director-General and WHO Western Pacific Regional Office (WPRO) Regional Director at the 67th session of the Regional Committee for the Western Pacific held in Manila in October 2016.

Impact of the Lymphatic Filariasis Control Program towards elimination of filariasis in Vanuatu, 1997-2006.

BACKGROUND: Lymphatic filariasis (LF) occurs when filarial parasites are transmitted to humans through mosquitoes. The filarial worms affect the lymphatic system which leads to abnormal enlargement of body parts, chronic pain, disability, and social discrimination. In 1999, a commitment was made to eliminate LF from the Pacific Region by 2010. The Pacific Program to Eliminate LF began, with Vanuatu being one of the 16 endemic countries included in this program. METHODS: In 1997/1998 a LF prevalence baseline survey was conducted to determine the need for mass drug administration (MDA) in Vanuatu. In 1999, the Vanuatu Lymphatic Filariasis Control Program was established, and nationwide MDA was implemented from 2000 to 2004. LF prevalence was collected during the MDA through sentinel site and spot check surveys, and after 5 years of MDA. MDA implementation methods included health worker training, social mobilization, and culturally appropriate health promotion strategies. RESULTS: LF prevalence at baseline was 4.79%; after MDA this declined to 0.16% in 2005/2006. Average MDA coverage ranged from 75.5-81.5% across 5 years. All three evaluation units surveyed in 2005/2006 were below the 1% threshold required to stop MDA. CONCLUSIONS: The LF Control Program between 1997 and 2006 was successful in reducing LF prevalence to <1%. High MDA coverage was a critical component of this success. This period of the Vanuatu LF Control Program played an important role in helping to eliminate LF in Vanuatu.

Surveillance efforts after mass drug administration to validate elimination of lymphatic filariasis as a public health problem in Vanuatu.

BACKGROUND: Vanuatu was formerly highly endemic for lymphatic filariasis (LF), caused by Wuchereria bancrofti and transmitted by Anopheles mosquitoes. After a baseline survey showing 4.8% antigen prevalence in 1998, the country conducted nationwide (in one implementation unit) annual mass drug administration (MDA) with albendazole and diethylcarbamazine citrate from 2000 to 2004 and achieved prevalence of 0.2% by 2006 in a representative nationwide cluster survey among all age groups. METHODS: Post MDA surveillance was conducted from 2006 to 2012. After MDA, the country was divided for surveillance into three evaluation units (EUs) formed by grouping provinces according to baseline prevalence: EU1: Torba, Sanma and Malampa; EU2: Penama; EU3: Shefa and Tafea. The study compiled all past data and information on surveys in Vanuatu from the country programme. This paper reviews the surveillance activities done after stopping MDA to validate the interruption of transmission and elimination of LF as a public health problem. RESULTS: Post-MDA surveillance consisting of at least three transmission assessment surveys (TAS) in each of the three EUs was conducted between 2006 and 2012. Sentinel and spot check surveys identified a few villages with persistent high prevalence; all antigen positive cases in these sites were treated and additional targeted MDA conducted for 3 years in 13 villages in one area of concern. All three EUs passed all TAS in 2007, 2010 and 2012 respectively, with no positives found except in EU2 (Penama province) in 2012 when 2 children tested positive for circulating filariasis antigen. Assessment of the burden of chronic filariasis morbidity found 95 cases in 2003 and 32 remaining cases in 2007, all aged over 60 years. CONCLUSIONS: Vanuatu has achieved validation of elimination of LF as a public health problem. Post-validation surveillance is still recommended especially in formerly highly endemic areas.

MDA-Lymphatic Filariasis.

Lymphatic filariasis is one of the neglected tropical diseases. It is estimated that 120 million people are currently infected in 73 countries where filariasis is endemic. Lymphatic filariasis is a leading cause of chronic disability worldwide, including of 15 million people who have lymphoedema (elephantiasis) and 25 million men who have hydrocoele.

Lymphatic filariasis in Papua New Guinea: distribution at district level and impact of mass drug administration, 1980 to 2011.

BACKGROUND: Lymphatic filariasis (LF) caused by Wuchereria bancrofti is present at high prevalence in some parts of Papua New Guinea. However, there has been no rigorous data-based representative assessment of nationwide prevalence of LF. The LF programme has been daunted by the scope of the problem, and progress on mass drug administration (MDA) has been slow and lacking in resources. METHODS: A systematic literature review identified LF surveys in Papua New Guinea between 1980 and 2011. Results were extracted by location, time period and test used (blood slide, immunochromatographic test (ICT) or Og4C3 ELISA) and combined by district. Three criteria schemes based on the Global Programme to Eliminate Lymphatic Filariasis guidelines, with modifications, were developed to classify and prioritize districts by prevalence level. Results of repeated surveys in the same sites were used to investigate the impact of MDA on LF prevalence over the time period. RESULTS: There were 312 distinct survey sites identified in 80 of the 89 districts over the 31-year period. The overall LF prevalence in the sites tested was estimated at 18.5 to 27.5% by blood slide for microfilariae (Mf), 10.1% to 12.9% by ICT and 45.4% to 48.8% by Og4C3. Biases in site selection towards areas with LF, and change in type of assay used, affected the prevalence estimates, but overall decline in prevalence over the time period was observed. Depending on the criteria used, 34 to 36 districts (population 2.7 to 2.9 million) were classed as high endemic (≥5% prevalence), 15 to 25 districts (1.7 to 1.9 million) as low endemic (<5%) and 20 to 31 (1.3 to 2.2 million) as non-endemic. Nine districts (0.7 million) had no information. The strong impact of MDA, especially on microfilaria (Mf) prevalence, was noted in sites with repeat surveys. CONCLUSIONS: This analytical review of past surveys of LF in Papua New Guinea enables better estimation of the national burden, identifies gaps in knowledge, quantifies and locates the population at risk, and can be used to predict the likely impact of MDA and/or vector control. Better targeting of districts by level of prevalence will strengthen the control programme, facilitate monitoring of the disease trend and increase the likelihood of reaching the target of LF elimination by 2020.

Preventive chemotherapy and the fight against neglected tropical diseases.

Preventive chemotherapy is the public health strategy recommended by the WHO against a set of neglected tropical diseases that includes four groups of helminth infections (lymphatic filariasis, onchocerciasis, schistosomiasis and soil-transmitted helminthiasis) and one chlamydial (trachoma) infection. This article presents the characteristics of preventive chemotherapy interventions directed against each disease targeted by this strategy and provides an update on the status of their implementation worldwide.

Eliminating lymphatic filariasis

One of the oldest of the neglected tropical diseases, lymphatic filariasis, is caused by filarial worms transmitted by insect vectors that live in the lymphatic system and most commonly cause lymphedema, elephantiasis and hydrocele, which may lead to severe deformity, stigma and disability. Similar to other neglected tropical diseases, lymphatic filariasis occurs mostly among the poor disenfranchised populations living in highly endemic settings perpetuating a cycle that traps people into further poverty and destitution. Through the leadership of the World Health Organization, the Global Programme to Eliminate Lymphatic Filariasis has reached substantial achievements in decreasing the transmission of lympahtic filariasis in multiple settings. The strategic plan for the next 10 years of the Global Programme, in addition to working within the new 'neglected tropical diseases environment,' lays out necessary mass drug administration implementation goals for the filariasis-endemic countries that have not yet started their elimination programs (principally in Africa). The neglected tropical diseases programs-and the lymphatic filariasis program in particular-are among the very least expensive, most cost-effective tools to benefit needy populations of the developing world.

Impact of five annual rounds of mass drug administration with diethylcarbamazine and albendazole on Wuchereria bancrofti infection in American Samoa.

American Samoa began a territory-wide mass drug administration (MDA) program with diethylcarbamazine and albendazole in 2000 after baseline surveys indicated that 16.5% of 2,989 residents were infected with Wuchereria bancrofti based on tests for circulating filarial antigen. Follow-up surveys were conducted in 2001, 2003, and 2006, using convenience samples of residents of sentinel villages. Antigenemia prevalence in 2001 (11.5%) and 2003 (13.5%) showed no change. After the 2003 sentinel assessment, improvements were made in the social mobilization and drug distribution strategies. In 2006, after a total of 5 years of MDA and 3 years of improved MDA participation, the antigenemia prevalence dropped from 11.5% (2001) to 0.95% (2006) (P < 0.0001). In 2006, antigenemia prevalence was greater in males (1.5%) than females (0.4%) (P = 0.04). The decline in antigenemia prevalence shows the effectiveness of MDA and changes made in social mobilization and drug distribution.

Lymphatic filariasis elimination in the Pacific: PacELF replicating Japanese success.

Japan successfully eliminated lymphatic filariasis and other parasitic diseases through community-driven, integrated nationwide campaigns undertaken during the 1960s and 1970s. The campaigns also created a cadre of experienced clinicians, scientists and public health workers with excellent technical and operational knowledge and a positive attitude towards filariasis elimination. These factors, and the humanitarian desire to improve health in neighbouring nations, influenced Japan to support filariasis control efforts overseas, starting in the 1970s and continuing through to the inception of the Pacific Programme to Eliminate Lymphatic Filariasis (PacELF) in 1999. The unique community-driven, self-help approach of Japan to disease control and health improvement profoundly influenced the activities of PacELF. PacELF is demonstrating that the successful national disease-elimination model in Japan can be extended to the regional level.

Pacific collaboration to eliminate lymphatic filariasis.

A regional programme to combat lymphatic filariasis in the Pacific islands is showing great promise as it reaches its halfway point. The Pacific Programme to Eliminate Lymphatic Filariasis (PacELF), established in 1999, aims to eliminate the disease from the Pacific by 2010 - ten years ahead of the global target. Set up with support from Australia, and now funded primarily by Japan and underpinned by the Word Health Organization, PacELF is providing evidence that Pacific nations can work cooperatively to rid the region of one of its worst scourges, in addition to discovering techniques and new tools that should be of use in other regions.

Laboratory studies of Ochlerotatus samoanus in association with leaf axils of Freycinetia (Pandanaceae) in Samoa.

Three species of Freycinetia (Pandanaceae) (F. reineckei, F. storkii, and F. hombronii) were tested for oviposition preference of Ochlerotatus samoanus, a vector of filariasis in Samoa. Laboratory tests indicated that F. reineckei was preferred by this mosquito for oviposition. Eggs were preferentially deposited on a peeled or a moist dried leaf. The percentage hatch was highest when eggs were kept moist for longer than 4 days before submersion. Hatching was complete in less than 6 h. These studies allowed us to successfully rear Oc. samoanus in the laboratory, facilitating future studies on the biology and control of this important vector.

The PacELF programme: will mass drug administration be enough?

The Pacific Programme to Eliminate Lymphatic Filariasis is a regional, mass drug administration-based campaign in 22 countries and territories with the aim of eliminating filariasis transmission and alleviating the suffering caused by Wuchereria bancrofti. The challenges to filariasis elimination campaigns based on mass drug-administration alone are reviewed in this article. These challenges together with the previous successes of mosquito control campaigns in eliminating filariasis from regions in the Pacific argue for inclusion of entomology components in the control of filariasis and the monitoring of filariasis elimination programs.