Russell Stothard Liverpool School of Tropical Medicine

UK

Interrupting schistosomiasis transmission:

Taking sensible steps in snail control in Cameroon

Louis-Albert Tchuem TchuentéCentre Schistosomiasis & Parasitology

Cameroon

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

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

China (CDC)/Cameroon initiative in schistosomiasis control

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)

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

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?)

Three stages of integrated control with mollusciciding

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

Barombi Kotto and Barombi Mbo: crater lakes

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

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

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

2017: Pinpointing key water contact sites

S. haematobiumPSAC (n=19) - 5.3%SAC (n=55) - 12.7%Adults (n=104) -12.5%

Mothers

PSAC (paired)

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

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

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

Linking concepts in transmission biology

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