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.

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. 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. 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. China (CDC)/Cameroon initiative in schistosomiasis control

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. 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. 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. Three stages of integrated control with mollusciciding

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. Barombi Kotto and Barombi Mbo: crater lakes

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. 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. 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. 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. 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. 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. 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. Linking concepts in transmission biology

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