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Why onchocerciasis transmission persists after 15 annual ivermectin mass drug administrations in South-West Cameroon
  1. Armelle Forrer1,
  2. Samuel Wanji2,3,
  3. Elisabeth Dibando Obie2,3,
  4. Theobald Mue Nji2,4,
  5. Louise Hamill1,
  6. Kim Ozano5,
  7. Helen Piotrowski5,
  8. Laura Dean5,
  9. Abdel J Njouendou2,3,
  10. Relindis Ekanya2,3,
  11. Winston Patrick Chounna Ndongmo2,3,
  12. Ebua Gallus Fung2,4,
  13. Dum-Buo Nnamdi2,4,
  14. Raphael A Abong2,3,
  15. Amuam Andrew Beng2,3,
  16. Mathias Esum Eyong2,3,
  17. Bertrand L Ndzeshang2,3,
  18. Desmond Akumtoh Nkimbeng2,3,
  19. Samuel Teghen2,3,
  20. Anicetus Suireng2,
  21. Ernerstine Ebot Ashu2,
  22. Emmanuel Kah2,3,
  23. Michele M Murdoch6,
  24. Rachael Thomson1,
  25. Sally Theobald5,
  26. Peter Enyong2,3,
  27. Joseph D Turner1,
  28. Mark J Taylor1
  1. 1 Centre for Neglected Tropical Diseases, Department of Tropical Disease Biology, Liverpool School of Tropical Medicine, Liverpool, Merseyside, UK
  2. 2 Department of Disease Control, Research Foundation for Tropical Diseases and the Environment (REFOTDE), Buea, Cameroon
  3. 3 Parasites and Vector Biology research unit (PAVBRU), Department of Microbiology and Parasitology, University of Buea, Buea, Cameroon
  4. 4 Department of Sociology and Anthropology, University of Buea, Buea, Cameroon
  5. 5 Department of International Public Health, Liverpool School of Tropical Medicine, Liverpool, Liverpool, UK
  6. 6 Watford General Hospital, West Herts Hospitals NHS Trust, Watford, UK
  1. Correspondence to Professor Mark J Taylor; Mark.Taylor{at}


Introduction Onchocerciasis is targeted for elimination mainly with annual community-directed treatment with ivermectin (CDTI). High infection levels have been reported in South-West Cameroon, despite ≥15 years of CDTI. The aim of this study was to assess factors associated with continued onchocerciasis transmission and skin disease.

Methods A large-scale cross-sectional study was conducted in 2017 in 20 communities in a loiasis-risk area in South-West Cameroon. A mixed-methods approach was used. Associations between infection levels, skin disease and adherence to CDTI were assessed using mixed regression modelling. Different community members’ perception and acceptability of the CDTI strategy was explored using semi-structured interviews.

Results Onchocerciasis prevalence was 44.4% among 9456 participants. 17.5% of adults were systematic non-adherers and 5.9% participated in ≥75% of CDTI rounds. Skin disease affected 1/10 participants, including children. Increasing self-reported adherence to CDTI was associated with lower infection levels in participants aged ≥15 years but not in children. Adherence to CDTI was positively influenced by perceived health benefits, and negatively influenced by fear of adverse events linked with economic loss. Concern of lethal adverse events was a common reason for systematic non-adherence.

Conclusion CDTI alone is unlikely to achieve elimination in those high transmission areas where low participation is commonly associated with the fear of adverse events, despite the current quasi absence of high-risk levels of loiasis. Such persisting historical memories and fear of ivermectin might impact adherence to CDTI also in areas with historical presence but current absence of loiasis. Because such issues are unlikely to be tackled by CDTI adaptive measures, alternative strategies are needed for onchocerciasis elimination where negative perception of ivermectin is an entrenched barrier to community participation in programmes.

  • onchocerciasis
  • parasitology
  • public health
  • control strategies
  • epidemiology

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  • AF and SW are joint first authors.

  • Handling editor Alberto L Garcia-Basteiro

  • Contributors SW, JDT, ST and MJT conceptualised the study. SW, JDT, ST and MJT acquired funding. SW, TMN, LH, ST, LD, KO, EGF and DBN contributed to the design of the qualitative study. SW, JDT, LH, AJN, RAA, ADO, EK, PCN and MJT contributed to the design of the quantitative parasitological study. SW, MEM, LH, JDT and MJT contributed to the design of the clinical assessments. EDO, AJN, RE, WPCN, RAA, AA, EME, BN, DAN, STe, EK, PE and LH collected the quantitative data. TMN, EGF and DBN collected the qualitative data. STe, AS and EEA conducted the clinical assessments.TMN, EGF, DBN, HP and KO analysed and interpreted the qualitative data. AF analysed and interpreted the quantitative data. AF, HP, KO wrote the first draft. All authors contributed to the second draft. All the authors approved the final manuscript.

  • Funding This study was funded by the Department for International Development (DFID), UK.

  • Competing interests None declared.

  • Patient consent for publication Not required.

  • Ethics approval This protocol was reviewed and approved by the Liverpool School of Tropical Medicine Research Ethics Committee (reference: 16–027), the Cameroonian National Ethics Committee for Research on Human Health (approval no. 2016/11/838/CE/CNERSH/SP) and the Division of Health Operations Research within the Cameroonian Ministry of Public Health (approval no. 631–03.17).

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data availability statement Data are available upon request. The data sets used and/or analysed during the current study are available from the corresponding author on reasonable request.

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  • Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.

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