1. School-based deworming and community-wide transmission of soil transmitted helminths
Déirdre Hollingsworth
University of Warwick
Liverpool School of Tropical Medicine

2. Soil-transmitted helminths
Burden of disease (WHO estimates)
Up to 1.2 billion people infected with one or more of the soil-transmitted helminths
135,000 deaths per year
Disabling effects
Anaemia
Stunted growth
Impaired cognitive development
Want to maximise impact of drug donations in London Declaration:
400m albendazole, GlaxoSmithKlein
200m mebendazole, Johnson & Johnson
Despommier D et al. Parasitic Diseases. 2001

3. Key questions for control of soil-transmitted infections by chemotherapy
What should be the target of control programmes?
Is elimination in a defined area possible by chemotherapy alone?
What are the best indicators for assessing the impact of control?
What level of infection across a community should trigger mass chemotherapy to minimise morbidity?
For a given transmission level, how often should mass or targeted chemotherapy be administered to sustain infection prevalence and intensity below defined levels?
Anderson, Hollingsworth et al Lancet (2012)

4. Key questions for control of soil-transmitted infections by chemotherapy
What should be the target of control programmes?
Is elimination in a defined area possible by chemotherapy alone?
What are the best indicators for assessing the impact of control?
What level of infection across a community should trigger mass chemotherapy to minimise morbidity?
For a given transmission level, how often should mass or targeted chemotherapy be administered to sustain infection prevalence and intensity below defined levels?
Anderson, Hollingsworth et al Lancet (2012)

5. Key questions for control of soil-transmitted infections by chemotherapy
What should be the target of control programmes?
Is elimination in a defined area possible by chemotherapy alone?
What are the best indicators for assessing the impact of control?
What level of infection across a community should trigger mass chemotherapy to minimise morbidity?
For a given transmission level, how often should mass or targeted chemotherapy be administered to sustain infection prevalence and intensity below defined levels?
Anderson, Hollingsworth et al Lancet (2012)

6. Key questions for control of soil-transmitted infections by chemotherapy
What should be the target of control programmes?
Is elimination in a defined area possible by chemotherapy alone?
What are the best indicators for assessing the impact of control?
What level of infection across a community should trigger mass chemotherapy to minimise morbidity?
For a given transmission level, how often should mass or targeted chemotherapy be administered to sustain infection prevalence and intensity below defined levels?
Anderson, Hollingsworth et al Lancet (2012)

7. Key questions for control of soil-transmitted infections by chemotherapy
What should be the target of control programmes?
Is elimination in a defined area possible by chemotherapy alone?
What are the best indicators for assessing the impact of control?
What level of infection across a community should trigger mass chemotherapy to minimise morbidity?
For a given transmission level, how often should mass or targeted chemotherapy be administered to sustain infection prevalence and intensity below defined levels?
Anderson, Hollingsworth et al Lancet (2012)

8. Key questions for control of soil-transmitted infections by chemotherapy
As the prevalence and intensity fall after repeated rounds of treatment, can the interval between treatments increase, and by how much?
How is the interval between treatments affected by the species mix in the community?
How do the demography of the population and the starting geographical distribution of infection affect the structure of optimum treatment programmes when resources are finite?
In terms of cost-effectiveness, is it best to target school children, those predisposed to heavy infection, or the entire community?
How might repeated mass treatment affect the evolution of drug resistance and how can this risk be minimised?
Anderson, Hollingsworth et al Lancet (2012)

9. Key questions for control of soil-transmitted infections by chemotherapy
As the prevalence and intensity fall after repeated rounds of treatment, can the interval between treatments increase, and by how much?
How is the interval between treatments affected by the species mix in the community?
How do the demography of the population and the starting geographical distribution of infection affect the structure of optimum treatment programmes when resources are finite?
In terms of cost-effectiveness, is it best to target school children, those predisposed to heavy infection, or the entire community?
How might repeated mass treatment affect the evolution of drug resistance and how can this risk be minimised?
Anderson, Hollingsworth et al Lancet (2012)

10. Key questions for control of soil-transmitted infections by chemotherapy
As the prevalence and intensity fall after repeated rounds of treatment, can the interval between treatments increase, and by how much?
How is the interval between treatments affected by the species mix in the community?
How do the demography of the population and the starting geographical distribution of infection affect the structure of optimum treatment programmes when resources are finite?
In terms of cost-effectiveness, is it best to target school children, those predisposed to heavy infection, or the entire community?
How might repeated mass treatment affect the evolution of drug resistance and how can this risk be minimised?
Anderson, Hollingsworth et al Lancet (2012)

11. Key questions for control of soil-transmitted infections by chemotherapy
As the prevalence and intensity fall after repeated rounds of treatment, can the interval between treatments increase, and by how much?
How is the interval between treatments affected by the species mix in the community?
How do the demography of the population and the starting geographical distribution of infection affect the structure of optimum treatment programmes when resources are finite?
In terms of cost-effectiveness, is it best to target school children, those predisposed to heavy infection, or the entire community?
How might repeated mass treatment affect the evolution of drug resistance and how can this risk be minimised?
Anderson, Hollingsworth et al Lancet (2012)

12. Key questions for control of soil-transmitted infections by chemotherapy
As the prevalence and intensity fall after repeated rounds of treatment, can the interval between treatments increase, and by how much?
How is the interval between treatments affected by the species mix in the community?
How do the demography of the population and the starting geographical distribution of infection affect the structure of optimum treatment programmes when resources are finite?
In terms of cost-effectiveness, is it best to target school children, those predisposed to heavy infection, or the entire community?
How might repeated mass treatment affect the evolution of drug resistance and how can this risk be minimised?
Anderson, Hollingsworth et al Lancet (2012)

13. Why school-based deworming?
Burden of disease in children
Existing infrastructure for delivery
Integration with other school health programmes
What is the impact on transmission?

14. Empirical studies
Reference
Main target
Country
Drug
Interval
Rounds
Age group targeted (yrs)
Impact on untreated
Asaolu et al (1991) Parasitology
Ascaris, Trichuris, Hookworm
Nigeria
levamisole
3 mths
4 (1yr)
2-15
Intensity, Ascaris only
Thein-Hliang et al (1990) WHO Bulletin
Ascaris
Myanmar
6 mths
2-4
(1-2yr)
1-19
1-14
5-19
Intensity and prevalence
Thein-Hliang et al (1991) Trans RSTMH 4
(1 yr)
<15
2--12
Bundy et al (1990) Trans RSTMH
Trichuris
Monserrat
albendazole
4 mths
2, 4
(8, 16 mths)
We need a framework for thinking about the impact of treating only 5-14 year olds

15. How many worms are exposed to treatment?
Demography
What proportion of population are school-aged?
Behaviour
What proportion of children attend school?
Epidemiology
What is the load of worms in children?
Anderson, Truscott, Pullan, Brooker, Hollingsworth PLoS NTDs (2013) in press

16. School attendance Enrolment varies by country, by age and by region
Attendance at deworming days may be higher than ordinary school days.
Source: UNICEF

17. How many worms are exposed to treatment?
Demography
What proportion of population are school-aged?
Behaviour
What proportion of children attend school?
Epidemiology
What is the load of worms in children?
Anderson, Truscott, Pullan, Brooker, Hollingsworth PLoS NTDs (2013) in press

18. Round worm High worm burdens in children
Anderson et al PLoS NTDs (2013) in press

19. Round worm High worm burdens in children 18%
Anderson et al PLoS NTDs (2013) in press

20. Round worm High worm burdens in children 18% 49% worms in 5-14yr olds
Anderson et al PLoS NTDs (2013) in press

21. Hookworm Lower burden in children
Anderson et al PLoS NTDs (2013) in press

22. Hookworm Lower burden in children 31%
Anderson et al PLoS NTDs (2013) in press

23. Hookworm Lower burden in children 31% 16% egg output in 5-14yr olds
Anderson et al PLoS NTDs (2013) in press

24. Impact on transmission
% of worms or output in school-age children is a crude calculation of likely impact
Impact on transmission depends on
Extent transmission from children to adults and younger children
Vice versa
Investigate scenarios using mathematical models

25. Two separate groups contributing equally to same infected pool
Treated group (30%) see much larger effect
Untreated group very little impact
Anderson et al PLoS NTDs (2013) in press

26. Children over-contribute to transmission
Starting intensity in untreated group is lower
Larger impact on this group of treating the children
Anderson et al PLoS NTDs (2013) in press

27. ? Programme impact A. lumbricoides Hookworm Drug efficacy ~80-90%
Demography X
Parasites
A. lumbricoides
Demography
% parasites in
school children
~10-50%
Hookworm
School
Enrolment
~20-90%
Impact
on transmission
X Parasites
Programme impact
% of parasites treated ?
More studies needed
Anderson et al PLoS NTDs (2013) in press

28. How to address this question
Monitoring impact of school-based treatment on whole communities
Whole age-profiles before and after treatment
Detailed studies of the dynamics of ‘bounce-back’ in adults and children
Robust parameter estimation
Trials of different treatment strategies
Genetic studies
Identifying transmission networks

29. Responding to programmatic need
Research questions
Field data
Control strategies
Mapping, monitoring & evaluation
Frequency of & targeting of treatment
Programme design
Research
Mapping, sampling
Epidemiology of transmission and control
Diagnostic design and evaluation
Programme design
Sampling frameworks
New tools

30. Acknowledgements Imperial College London
Professor Sir Roy Anderson
Dr James Truscott
Helminth researchers
London School of Hygiene and Tropical Medicine
Professor Simon Brooker
Dr Rachel Pullan
Funders
Bill and Melinda Gates Foundation
Partnership for Child Development
Imperial College Junior Research Fellowship