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

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Abstract

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.

Section snippets

Background

Lymphatic filariasis (LF) is a helminthic human disease transmitted by mosquito vectors. Three species of filarial worms exist worldwide: Wuchereria bancrofti, Brugia malayi and B. timori, which are transmitted by Anopheles, Aedes, Culex and Mansonia mosquitoes (WHO, 2020c). Lymphatic filariasis can lead to severe chronic disability and disfigurement, as a result of lymphoedema, including swollen limbs (elephantiasis) and hydrocoele (scrotal swelling) in men. Initial symptoms may take 5–10 years

Samoa

Samoa is a South Pacific nation comprising two main islands, Upolu and Savai'i, and six islets located approximately between 13 and 14 degree S and 172 degree W, with a land area of 2935 km2. The estimated population grew from 176,710 to 187,820 between the 2001 and 2011 censuses. At the most recent census in 2016, the population was estimated as 191,126, with 93% Samoan ethnicity (Samoa Bureau of Statistics, 2016a). The capital Apia is located on Upolu. There are four administrative regions with

Methods

Data were extracted from published and unpublished reports from 1998 to 2017. Site and village survey records (numbers tested and positive by ICT or Mf blood slide) and MDA coverages were extracted from PacELF reports, the 2003 and 2006 PacELF databooks (WHO WPRO, 2003, WHO WPRO, 2006a) and the PacELF Way book (WHO WPRO, 2006b). Survey sites were usually villages, but sometimes there were multiple survey sites in the same village. Information was extracted from documents held at the PacELF

Programme overview

The timeline of elimination activities (programme and policy events, surveys and MDAs implemented) is shown in Table 1. A (mapping) surveys using ICT antigen tests and Mf slides to determine baseline endemicity began in Samoa in 1998 and continued in 1999, providing data to support the policy that MDA was required everywhere in the country. MDAs under PacELF began in 1999, after the A survey was completed.

Timing and number of participants for blood and other surveys, and years of MDA

Discussion

The extensive and fine-detailed information on LF and its control programme in Samoa from 1998 to 2017 has not previously been carefully collated, evaluated, disseminated or used to best advantage. Information for this 20-year period is presented here to describe the control programme activities and strategies, document all the detailed survey results, and clarify the prevalence and geographical distribution of infection prevalence over time.

The data have some limitations, including the

Conclusions

There was a large reduction in Ag and Mf prevalence in Samoa between 1998 and 2004, likely due to the five rounds of MDA 1999–2003, but elimination thresholds were not reached. Prevalence apparently increased slightly from 2004 to 2007, and was not impacted by intermittent MDAs since then, resulting in a clear resurgence by 2017 as shown in nationwide TAS.

Samoa's MOH has devoted attention and resources in a comprehensive and organized LF MDA programme for many years. Although there was good

Acknowledgements

The Samoa LF programme during the period of study was supported by the Government of Samoa, PacELF/the WHO Division of Pacific Support in Suva Fiji, WHO Geneva, WHO Western Pacific Regional Office, the Australian Government through AusAID, the Secretariat of the Pacific Community, US Centers for Disease Control and Prevention, the Japanese Government, and Japan International Cooperation Agency. James Cook University provided technical support and advice through the WHO Collaborating Centre (CC)

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    • †

    Current address: West Melbourne, VIC, Australia.

    ‡

    Current address: Communicable Disease Control Branch, SA Health, Adelaide, SA, Australia.

    §

    Current address: Mossman, QLD, Australia.

    Current address: Castle Hill, NSW, Australia.

    ||

    Current address: Department of Environmental Biology and Medical Parasitology; College of Medicine, Hanyang University, Seoul, Republic of Korea.

    **

    Current address: Portland, OR, United States.

    ††

    Current address: Tokyo, Japan.

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