Elimination of lymphatic filariasis (LF) in the Pacific Island Countries and Territories (PICT) has been defined as <0.1% circulating filarial antigen (CFA) prevalence in children born after the implementation of successful mass drug administrations (MDAs). This research assessed the feasibility of CFA and antibody testing in three countries; Tonga, Vanuatu, and Samoa. Transmission is interrupted in Vanuatu and Tonga as evidenced by no CFA positive children and a low antibody prevalence and titre. Transmission is ongoing in Samoa with microfilaraemic (Mf) and CFA positive children and a high antibody prevalence and titre. Furthermore, areas of transmission were identified with Mf positive adults, but no CFA positive children. These areas had a high antibody prevalence in children. In conclusion, CFA testing in children alone was not useful for identifying areas of residual endemicity in Samoa. Thus, it would be beneficial to include antibody serology in the PICT surveillance strategy. 1. Introduction Lymphatic filariasis (LF), a mosquito-transmitted parasitic disease caused by the filarial nematodes Wuchereria bancrofti, Brugia malayi, and Brugia timori, is classified as a neglected tropical disease (NTD) that is endemic in many parts of the world including the South Pacific [1–3]. The Global Elimination Programme to eliminate LF (GPELF) began in the late 1990s, and the Pacific counterpart of GPELF, formed in 1999 under the auspices of the World Health Organization (WHO), was named the Pacific Programme for the Elimination of Lymphatic Filariasis (PacELF) [4, 5]. PacELF resolved to eliminate LF as a public health problem in the Pacific using mass drug administrations (MDAs) [5]. Elimination of LF was defined as <1% circulating filarial antigen (CFA) prevalence of the population and <0.1% CFA prevalence in children born after the implementation of MDAs [6]. Sixteen of the 22 countries falling under the jurisdiction of PacELF were classified as endemic for LF following baseline prevalence surveys. They were American Samoa, the Cook Islands, the Federated States of Micronesia, Fiji, French Polynesia, Kiribati, the Marshall Islands, New Caledonia, Niue, Palau, Papua New Guinea, Samoa, Tonga, Tuvalu, Vanuatu, and Wallis and Futuna [7]. The Cook Islands, Niue, Vanuatu, and Tonga have reached <1% CFA prevalence of the population following five rounds of MDA and are now implementing activities to ensure that transmission has been interrupted and to detect any remaining and/or new foci of transmission [8]. The challenge for this phase of the LF programme is to
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