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Interrupting Schistosomiasis Transmission: Taking sensible steps in Snail Control in Cameroon

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This presentation was given by Prof. Russell Stothard, at the ISNTD Bites event that took place on Tuesday, 19th July 2017. It highlights the work being done in Cameroon to control Schistosomiasis transmission by reducing the snail population.

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Interrupting Schistosomiasis Transmission: Taking sensible steps in Snail Control in Cameroon

  1. 1. Russell Stothard Liverpool School of Tropical Medicine UK Interrupting schistosomiasis transmission: Taking sensible steps in snail control in Cameroon Louis-Albert Tchuem Tchuenté Centre Schistosomiasis & Parasitology Cameroon
  2. 2. Contents Background on snail control with mollusicides - Use of Baylucide and ‘combustible haystack’ models Situation assessment & preliminary implementation plan - Targeting appropriate snail control to key water contact sites Crater lakes of Cameroon – Barombi Kotto & Mbo - Epidemiological surveillance of urogenital schistosomiasis
  3. 3. Integrated control with chemical molluscicides • Preventive chemotherapy with praziquantel alongside other interventions • Focal application of Baylucide® (niclosamide), NB: Chinese manufacturers In 2017 WHO’s new interest
  4. 4. China (CDC)/Cameroon initiative in schistosomiasis control
  5. 5. Towards integrated control with chemical mollusciciding • New suppliers of various niclosamide formulations in China Pilot formulations available for testing NB: key differences in African & Chinese snails (aquatic versus amphibious)
  6. 6. Snail control: the ‘burning haystack’ model of at-risk habitats Strike the match (single or multiple events) input of viable miracidia (non)permissive host snails aquatic habitat/shoreline (a snail haystack) add human/animal behaviour two major outcomes active transmission potential permissive snails no transmission potential X refractory snails
  7. 7. Snail control: the ‘burning haystack’ model of at-risk habitats (non)permissive host snails aquatic habitat/shoreline No haystack No snails (or at least sufficiently reduced) No transmission (how long & at what cost?)
  8. 8. Three stages of integrated control with mollusciciding
  9. 9. Contents Background on snail control with mollusicides - Use of Baylucide and ‘combustible haystack’ models Situation assessment & preliminary implementation plan - Targeting appropriate snail control to key water contact sites Crater lakes of Cameroon – Barombi Kotto & Mbo - Epidemiological surveillance of urogenital schistosomiasis
  10. 10. Barombi Kotto and Barombi Mbo: crater lakes
  11. 11.  Significant decline of SCH prevalence from: • 82% to 46% in Kotto • 62% to 3% in Mbo  Low STH prevalence: 6% (decrease of 79% over the past decade) At Mbo, installation of piped water and sandbox filters for household drinking water At Kotto, total dependence on water from the Lake  Intense water contacts Barombi Kotto and Barombi Mbo: crater lakes • Two well-known hotspots of urogenital schistosomiasis (NB: limnology) • COUNTDOWN multi-disciplinary surveys started in 2016 at each lake
  12. 12. Barombi Kotto: greater effort of interventions required • Community-wide treatment & initial projected IEC lecture (2016) at Kotto • First provision of PZQ for expanded access to treatment by island-CDD
  13. 13. Malacological survey in 2016 and 2017 Bulinus camerunensis intermediate host • ‘endemic’ & type species Indoplanorbis exustus (an alien invader) A non-host snail and miracidial decoy? shedding
  14. 14. 2017: Pinpointing key water contact sites S. haematobium PSAC (n=19) - 5.3% SAC (n=55) - 12.7% Adults (n=104) -12.5% Mothers PSAC (paired)
  15. 15. Be prepared for surprises with freshwater aliens • Long range colonisation event of Clade E in Cameroon – where next? How to use molluscide in Kotto? •kills fish / fishing v. important •geographical coverage •deep/shallow water sites Pilot LD50 experiments needed Community awareness/acceptance
  16. 16. Pilot laboratory experiments  Bulinus camerunensis appears easier to kill  Indoplanorbis exustus as a neutral indication? • molluscicide sentinel (differing population biology) • miracidial contamination (sentinel deployment)  Slow release formulation in chained floating dispensers
  17. 17. Contents Background on snail control with mollusicides - Use of Baylucide and ‘combustible haystack’ models Situation assessment & preliminary implementation plan - Targeting appropriate snail control to key water contact sites Crater lakes of Cameroon – Barombi Kotto & Mbo - Epidemiological surveillance of urogenital schistosomiasis
  18. 18. Linking concepts in transmission biology
  19. 19. Thank you ISNTD Bites COUNTDOWN ICST-2 Suzanne Campbell (LSTM) Lucas Cunningham Faye O’Halloran Deborah Sankey Tim Durant Grace Macklin Lisa O’Halloran Zikmund Bartoníček James LaCourse Martyn Stewart Emily Adams CSP team Roland Ombede & Gwladys Chiunteu Estelle Koukouam Magne (Catholic Uni C. Afr.) Hermine Jatsa Boukeng (Uni of Yaoundé I) Supporting the COUNTDOWN consortium NHM David Rollinson Bonnie Webster Univ. Melbourne Neil Young Tilburg Hospital Jaco Verweij Acknowledgements

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