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Peer-reviewedCC BYPLOS Neglected Tropical Diseases

Evaluating the impact of triple-drug mass drug administration using human and mosquito-based indicators of lymphatic filariasis in Samoa, 2019 – 2024

  • Helen J. Mayfield1
  • Angus McLure2
  • Lisa Rigby3
  • Brady McPherson4
  • Richard Bradbury5
  • Shannon M. Hedtke6
  • Rhys Izuagbe7
  • Joanne Kizu8
  • Donna MacKenzie9
  • Elina Panahi
  • Beatris Mario Martin
  • Benn Sartorius
6 more authors
  • Asrhyella Seeler
  • Selina Ward
  • Robert Thomsen
  • Satupaitea Viali
  • Patricia M. Graves
  • Colleen L. Lau
9 affiliations
  1. 1Faculty of Health, Medicine and Behavioural Sciences, University of Queensland Centre for Clinical Research, The University of Queensland, Brisbane, Queensland, Australia
  2. 2National Centre for Epidemiology and Population Health, Australian National University, Canberra, Australian Capital Territory, Australia
  3. 3Australian Defence Force Malaria and Infectious Disease Institute, Enoggera, Queensland, Australia
  4. 4College of Medicine and Dentistry, James Cook University, Cairns, Queensland, Australia
  5. 5Institute of Innovation, Science and Sustainability, Federation University, Berwick, Victoria, Australia
  6. 6La Trobe Institute for Molecular Science, School of Agriculture, Biomedicine and Environment, La Trobe University, Bundoora, Victoria, Australia
  7. 7QIMR Berghofer Institute of Medical Research, Brisbane, Queensland, Australia
  8. 8Samoa Ministry of Health, Apia, Samoa
  9. 9Oceania University of Medicine Samoa, Apia, Samoa
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Abstract

Background: For lymphatic filariasis (LF) elimination, the World Health Organization recommends multiple rounds of mass drug administration (MDA) to interrupt transmission. While LF antigen (Ag) is routinely used to monitor progress, recent evidence suggests more time-sensitive indicators are needed during the immediate post-MDA period. In Samoa, triple-drug MDA was distributed in 2018 and 2023. This study aimed to evaluate the impact of Samoa’s second round of triple-drug MDA on human and mosquito-based indicators of transmission. Methodology: Surveys were conducted in eight primary sampling units (PSUs) in 2019 (6–9 months after the 2018 MDA), 2023 (4.5 years after the 2018 MDA) and 2024 (10 months after the 2023 MDA). Participants aged ≥5 years from randomly selected households were tested for Ag and microfilariae (Mf). For molecular xenomonitoring (MX), mosquitoes were caught using BG-Sentinel traps at households, sorted into pools by species, and tested for presence of filarial DNA using quantitative polymerase chain reaction (qPCR). Results and key findings: In 2024, Ag prevalence was 10.3% (95% CI: 7.3-14.5) versus 9.9% (95% CI: 3.5-21.0) in 2023 and 9.8% (95% CI: 5.6-15.5) in 2019. Mf prevalence was 3.1% (95% CI: 1.8-5.5) in 2024 vs 5.1% (95% CI:1.3-12.4) in 2023 and 3.1% (95% CI:1.3-5.9) in 2019. Odds ratios (OR) of a positive test in 2024 vs 2023 showed no decrease for Ag (OR 1.0; 95% CI: 0.7-1.6), but a potential reduction in the proportion of Ag-positive participants who were Mf-positive (OR 0.6; 95% CI: 0.2-1.4) and a significant reduction in the prevalence of qPCR-positive mosquitoes (OR 0.4; 95% CrI: 0.2-0.7). From 2019–2024, there were reductions in prevalence of qPCR-positive Aedes spp. (OR 0.5; 95% CrI: 0.3-1.0) and Aedes polynesiensis (OR 0.4; 95% CrI: 0.2-0.8). Conclusions: In Samoa, LF transmission continues despite two rounds of triple-drug MDA five years apart. Mosquito indicators can provide a more sensitive measure of MDA impact in the immediate post-intervention period and complement human indicators for long-term surveillance. Author summary: Lymphatic filariasis is a mosquito-borne disease that can cause severe long-term disability. To eliminate this neglected tropical disease as a public health problem, the World Health Organization (WHO) recommends multiple rounds of mass drug administration (MDA) 12 months apart. Despite antigen (Ag) being the standard indicator for evaluating MDA impact, more time-sensitive indicators, such as measuring microfilariae (Mf) in the blood or testing mosquitoes for filarial DNA (molecular xenomonitoring), may provide a more reliable assessment in the months following the intervention. Samoa distributed triple-drug MDA in 2018 and 2023. We evaluated the impact of the second round on human and mosquito-based infection indicators including Ag, Mf, and qPCR-positive mosquitoes. We surveyed eight villages in Samoa in 2019 (6–9 months after the 2018 MDA), 2023 (4.5 years after the 2018 MDA) and 2024 (10 months after the 2023 MDA). The two rounds of MDA were insufficient to break the LF transmission cycle. Results from 2024 showed no decrease in Ag prevalence from either 2019 or 2023, although there was potentially a decrease in Mf prevalence. Molecular xenomonitoring (MX) provided an earlier signal of MDA impact than Ag, with a decrease in the prevalence of qPCR-positive mosquitoes observed within 10 months of the 2023 MDA.

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Cite

BibTeXRIS
BibTeX
@article{mayfield2026evaluating,
  title = {{Evaluating the impact of triple-drug mass drug administration using human and mosquito-based indicators of lymphatic filariasis in Samoa, 2019 – 2024}},
  author = {Helen J. Mayfield and Angus McLure and Lisa Rigby and Brady McPherson and Richard Bradbury and Shannon M. Hedtke and Rhys Izuagbe and Joanne Kizu and Donna MacKenzie and Elina Panahi and Beatris Mario Martin and Benn Sartorius and Asrhyella Seeler and Selina Ward and Robert Thomsen and Satupaitea Viali and Patricia M. Graves and Colleen L. Lau},
  journal = {PLOS Neglected Tropical Diseases},
  year = {2026},
  month = oct,
  doi = {10.1371/journal.pntd.0013895},
  url = {https://journals.plos.org/plosntds/article?id=10.1371/journal.pntd.0013895},
  note = {CC BY},
}
RIS
TY  - JOUR
TI  - Evaluating the impact of triple-drug mass drug administration using human and mosquito-based indicators of lymphatic filariasis in Samoa, 2019 – 2024
AU  - Helen J. Mayfield
AU  - Angus McLure
AU  - Lisa Rigby
AU  - Brady McPherson
AU  - Richard Bradbury
AU  - Shannon M. Hedtke
AU  - Rhys Izuagbe
AU  - Joanne Kizu
AU  - Donna MacKenzie
AU  - Elina Panahi
AU  - Beatris Mario Martin
AU  - Benn Sartorius
AU  - Asrhyella Seeler
AU  - Selina Ward
AU  - Robert Thomsen
AU  - Satupaitea Viali
AU  - Patricia M. Graves
AU  - Colleen L. Lau
PY  - 2026
DA  - 2026/10/01
JO  - PLOS Neglected Tropical Diseases
DO  - 10.1371/journal.pntd.0013895
UR  - https://journals.plos.org/plosntds/article?id=10.1371/journal.pntd.0013895
AB  - Background: For lymphatic filariasis (LF) elimination, the World Health Organization recommends multiple rounds of mass drug administration (MDA) to interrupt transmission. While LF antigen (Ag) is routinely used to monitor progress, recent evidence suggests more time-sensitive indicators are needed during the immediate post-MDA period. In Samoa, triple-drug MDA was distributed in 2018 and 2023. This study aimed to evaluate the impact of Samoa’s second round of triple-drug MDA on human and mosquito-based indicators of transmission. Methodology: Surveys were conducted in eight primary sampling units (PSUs) in 2019 (6–9 months after the 2018 MDA), 2023 (4.5 years after the 2018 MDA) and 2024 (10 months after the 2023 MDA). Participants aged ≥5 years from randomly selected households were tested for Ag and microfilariae (Mf). For molecular xenomonitoring (MX), mosquitoes were caught using BG-Sentinel traps at households, sorted into pools by species, and tested for presence of filarial DNA using quantitative polymerase chain reaction (qPCR). Results and key findings: In 2024, Ag prevalence was 10.3% (95% CI: 7.3-14.5) versus 9.9% (95% CI: 3.5-21.0) in 2023 and 9.8% (95% CI: 5.6-15.5) in 2019. Mf prevalence was 3.1% (95% CI: 1.8-5.5) in 2024 vs 5.1% (95% CI:1.3-12.4) in 2023 and 3.1% (95% CI:1.3-5.9) in 2019. Odds ratios (OR) of a positive test in 2024 vs 2023 showed no decrease for Ag (OR 1.0; 95% CI: 0.7-1.6), but a potential reduction in the proportion of Ag-positive participants who were Mf-positive (OR 0.6; 95% CI: 0.2-1.4) and a significant reduction in the prevalence of qPCR-positive mosquitoes (OR 0.4; 95% CrI: 0.2-0.7). From 2019–2024, there were reductions in prevalence of qPCR-positive Aedes spp. (OR 0.5; 95% CrI: 0.3-1.0) and Aedes polynesiensis (OR 0.4; 95% CrI: 0.2-0.8). Conclusions: In Samoa, LF transmission continues despite two rounds of triple-drug MDA five years apart. Mosquito indicators can provide a more sensitive measure of MDA impact in the immediate post-intervention period and complement human indicators for long-term surveillance. Author summary: Lymphatic filariasis is a mosquito-borne disease that can cause severe long-term disability. To eliminate this neglected tropical disease as a public health problem, the World Health Organization (WHO) recommends multiple rounds of mass drug administration (MDA) 12 months apart. Despite antigen (Ag) being the standard indicator for evaluating MDA impact, more time-sensitive indicators, such as measuring microfilariae (Mf) in the blood or testing mosquitoes for filarial DNA (molecular xenomonitoring), may provide a more reliable assessment in the months following the intervention. Samoa distributed triple-drug MDA in 2018 and 2023. We evaluated the impact of the second round on human and mosquito-based infection indicators including Ag, Mf, and qPCR-positive mosquitoes. We surveyed eight villages in Samoa in 2019 (6–9 months after the 2018 MDA), 2023 (4.5 years after the 2018 MDA) and 2024 (10 months after the 2023 MDA). The two rounds of MDA were insufficient to break the LF transmission cycle. Results from 2024 showed no decrease in Ag prevalence from either 2019 or 2023, although there was potentially a decrease in Mf prevalence. Molecular xenomonitoring (MX) provided an earlier signal of MDA impact than Ag, with a decrease in the prevalence of qPCR-positive mosquitoes observed within 10 months of the 2023 MDA.
SN  - 1935-2735
SN  - 1935-2727
ER  -