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Observed reductions in Schistosoma mansoni transmission from large-scale administration of praziquantel in Uganda: a mathematical modelling study.

French MD, Churcher TS, Gambhir M, Fenwick A, Webster JP, Kabatereine NB, Basáñez MG - PLoS Negl Trop Dis (2010)

Bottom Line: In this study, a mathematical modelling approach was used to estimate reductions in the rate of Schistosoma mansoni reinfection following annual mass drug administration (MDA) with praziquantel in Uganda over four years (2003-2006).MDA achieved substantial and statistically significant reductions in the FOI following one round of treatment in areas of low baseline infection intensity, and following two rounds in areas with high and medium intensities.The results indicate that the Schistosomiasis Control Initiative, as a model for other MDA programmes, is likely exerting a significant ancillary impact on reducing transmission within the community, and may provide health benefits to those who do not receive treatment.

View Article: PubMed Central - PubMed

Affiliation: Schistosomiasis Control Initiative, Imperial College London, London, United Kingdom. michael.french05@imperial.ac.uk

ABSTRACT

Background: To date schistosomiasis control programmes based on chemotherapy have largely aimed at controlling morbidity in treated individuals rather than at suppressing transmission. In this study, a mathematical modelling approach was used to estimate reductions in the rate of Schistosoma mansoni reinfection following annual mass drug administration (MDA) with praziquantel in Uganda over four years (2003-2006). In doing this we aim to elucidate the benefits of MDA in reducing community transmission.

Methods: Age-structured models were fitted to a longitudinal cohort followed up across successive rounds of annual treatment for four years (Baseline: 2003, TREATMENT: 2004-2006; n = 1,764). Instead of modelling contamination, infection and immunity processes separately, these functions were combined in order to estimate a composite force of infection (FOI), i.e., the rate of parasite acquisition by hosts.

Results: MDA achieved substantial and statistically significant reductions in the FOI following one round of treatment in areas of low baseline infection intensity, and following two rounds in areas with high and medium intensities. In all areas, the FOI remained suppressed following a third round of treatment.

Conclusions/significance: This study represents one of the first attempts to monitor reductions in the FOI within a large-scale MDA schistosomiasis morbidity control programme in sub-Saharan Africa. The results indicate that the Schistosomiasis Control Initiative, as a model for other MDA programmes, is likely exerting a significant ancillary impact on reducing transmission within the community, and may provide health benefits to those who do not receive treatment. The results obtained will have implications for evaluating the cost-effectiveness of schistosomiasis control programmes and the design of monitoring and evaluation approaches in general.

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Related in: MedlinePlus

Impact of treatment on categories of infection intensity in treated and untreated populations.This shows the change in the proportion of people within each infection intensity category following praziquantel treatment. The left-hand column shows the observed figures from the baseline longitudinal and cross-sectional cohorts (data points and error bars representing 95% confidence intervals derived from 100,000 bootstrap repetitions with replacement) compared to the model-derived values (shaded areas). The right-hand column shows the predicted reduction in categories of infection intensity in those school-age children who do not receive treatment, using Uganda-specific demographic structure. Thus, any reduction in the prevalence of heavy infection in the latter will be due to changes in the FOI. Red = heavy infection (≥400 epg); dark orange = moderate infection (100–399 epg); light orange = light infection (1–99 epg), pale yellow = uninfected (0 epg). The upper, middle, and bottom rows refer, respectively, to areas of high, medium, and low intensity at baseline, as defined in Figure 1. The years correspond to: 2002–2003: baseline; 2004: follow up year 1; 2005: follow up year 2; 2006: follow up year 3.
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pntd-0000897-g004: Impact of treatment on categories of infection intensity in treated and untreated populations.This shows the change in the proportion of people within each infection intensity category following praziquantel treatment. The left-hand column shows the observed figures from the baseline longitudinal and cross-sectional cohorts (data points and error bars representing 95% confidence intervals derived from 100,000 bootstrap repetitions with replacement) compared to the model-derived values (shaded areas). The right-hand column shows the predicted reduction in categories of infection intensity in those school-age children who do not receive treatment, using Uganda-specific demographic structure. Thus, any reduction in the prevalence of heavy infection in the latter will be due to changes in the FOI. Red = heavy infection (≥400 epg); dark orange = moderate infection (100–399 epg); light orange = light infection (1–99 epg), pale yellow = uninfected (0 epg). The upper, middle, and bottom rows refer, respectively, to areas of high, medium, and low intensity at baseline, as defined in Figure 1. The years correspond to: 2002–2003: baseline; 2004: follow up year 1; 2005: follow up year 2; 2006: follow up year 3.

Mentions: A reduction in the numbers of people harbouring heavy infection (and who will thus be most likely to suffer from current and future morbidity) is clearly paramount from a morbidity control programme perspective. In high intensity areas the prevalence of heavy infection (proportion of individuals excreting ≥400 epg) fell from 47% (95%CI: 43–51) at baseline to 8% (95%CI: 0–19) after 3 rounds of treatment (a reduction of 83%, P<0.001). Similarly in areas with an average moderate intensity at baseline (100–399 epg), the percentage of individuals harbouring heavy intensity infections fell from 17% (95%CI: 13–22%) to 3% (95%CI: 0–15%) (a reduction of 83%, P<0.001). In areas of low intensity at baseline (<100 epg), the prevalence of those harbouring heavy infection fell from 1.91% (95%CI: 0–6.0%) to 0.33% (95%CI: 0–8.3%); a fall of 82.5% (P = 0.01). Figure 4 shows the reductions in the frequency of infection category in the different areas. The left-hand column demonstrates the fit of the model to observed frequencies of infection category in the longitudinal cohort. Parameter values obtained from fitting the model were then used to make predictions regarding the effect of MDA on the untreated human population. Using Uganda-specific demography, the impact of treatment on those school-age children (aged 6–15 yr) who did not receive treatment is shown in the right-hand column. Any changes here are caused purely by reductions in FOI.


Observed reductions in Schistosoma mansoni transmission from large-scale administration of praziquantel in Uganda: a mathematical modelling study.

French MD, Churcher TS, Gambhir M, Fenwick A, Webster JP, Kabatereine NB, Basáñez MG - PLoS Negl Trop Dis (2010)

Impact of treatment on categories of infection intensity in treated and untreated populations.This shows the change in the proportion of people within each infection intensity category following praziquantel treatment. The left-hand column shows the observed figures from the baseline longitudinal and cross-sectional cohorts (data points and error bars representing 95% confidence intervals derived from 100,000 bootstrap repetitions with replacement) compared to the model-derived values (shaded areas). The right-hand column shows the predicted reduction in categories of infection intensity in those school-age children who do not receive treatment, using Uganda-specific demographic structure. Thus, any reduction in the prevalence of heavy infection in the latter will be due to changes in the FOI. Red = heavy infection (≥400 epg); dark orange = moderate infection (100–399 epg); light orange = light infection (1–99 epg), pale yellow = uninfected (0 epg). The upper, middle, and bottom rows refer, respectively, to areas of high, medium, and low intensity at baseline, as defined in Figure 1. The years correspond to: 2002–2003: baseline; 2004: follow up year 1; 2005: follow up year 2; 2006: follow up year 3.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2990705&req=5

pntd-0000897-g004: Impact of treatment on categories of infection intensity in treated and untreated populations.This shows the change in the proportion of people within each infection intensity category following praziquantel treatment. The left-hand column shows the observed figures from the baseline longitudinal and cross-sectional cohorts (data points and error bars representing 95% confidence intervals derived from 100,000 bootstrap repetitions with replacement) compared to the model-derived values (shaded areas). The right-hand column shows the predicted reduction in categories of infection intensity in those school-age children who do not receive treatment, using Uganda-specific demographic structure. Thus, any reduction in the prevalence of heavy infection in the latter will be due to changes in the FOI. Red = heavy infection (≥400 epg); dark orange = moderate infection (100–399 epg); light orange = light infection (1–99 epg), pale yellow = uninfected (0 epg). The upper, middle, and bottom rows refer, respectively, to areas of high, medium, and low intensity at baseline, as defined in Figure 1. The years correspond to: 2002–2003: baseline; 2004: follow up year 1; 2005: follow up year 2; 2006: follow up year 3.
Mentions: A reduction in the numbers of people harbouring heavy infection (and who will thus be most likely to suffer from current and future morbidity) is clearly paramount from a morbidity control programme perspective. In high intensity areas the prevalence of heavy infection (proportion of individuals excreting ≥400 epg) fell from 47% (95%CI: 43–51) at baseline to 8% (95%CI: 0–19) after 3 rounds of treatment (a reduction of 83%, P<0.001). Similarly in areas with an average moderate intensity at baseline (100–399 epg), the percentage of individuals harbouring heavy intensity infections fell from 17% (95%CI: 13–22%) to 3% (95%CI: 0–15%) (a reduction of 83%, P<0.001). In areas of low intensity at baseline (<100 epg), the prevalence of those harbouring heavy infection fell from 1.91% (95%CI: 0–6.0%) to 0.33% (95%CI: 0–8.3%); a fall of 82.5% (P = 0.01). Figure 4 shows the reductions in the frequency of infection category in the different areas. The left-hand column demonstrates the fit of the model to observed frequencies of infection category in the longitudinal cohort. Parameter values obtained from fitting the model were then used to make predictions regarding the effect of MDA on the untreated human population. Using Uganda-specific demography, the impact of treatment on those school-age children (aged 6–15 yr) who did not receive treatment is shown in the right-hand column. Any changes here are caused purely by reductions in FOI.

Bottom Line: In this study, a mathematical modelling approach was used to estimate reductions in the rate of Schistosoma mansoni reinfection following annual mass drug administration (MDA) with praziquantel in Uganda over four years (2003-2006).MDA achieved substantial and statistically significant reductions in the FOI following one round of treatment in areas of low baseline infection intensity, and following two rounds in areas with high and medium intensities.The results indicate that the Schistosomiasis Control Initiative, as a model for other MDA programmes, is likely exerting a significant ancillary impact on reducing transmission within the community, and may provide health benefits to those who do not receive treatment.

View Article: PubMed Central - PubMed

Affiliation: Schistosomiasis Control Initiative, Imperial College London, London, United Kingdom. michael.french05@imperial.ac.uk

ABSTRACT

Background: To date schistosomiasis control programmes based on chemotherapy have largely aimed at controlling morbidity in treated individuals rather than at suppressing transmission. In this study, a mathematical modelling approach was used to estimate reductions in the rate of Schistosoma mansoni reinfection following annual mass drug administration (MDA) with praziquantel in Uganda over four years (2003-2006). In doing this we aim to elucidate the benefits of MDA in reducing community transmission.

Methods: Age-structured models were fitted to a longitudinal cohort followed up across successive rounds of annual treatment for four years (Baseline: 2003, TREATMENT: 2004-2006; n = 1,764). Instead of modelling contamination, infection and immunity processes separately, these functions were combined in order to estimate a composite force of infection (FOI), i.e., the rate of parasite acquisition by hosts.

Results: MDA achieved substantial and statistically significant reductions in the FOI following one round of treatment in areas of low baseline infection intensity, and following two rounds in areas with high and medium intensities. In all areas, the FOI remained suppressed following a third round of treatment.

Conclusions/significance: This study represents one of the first attempts to monitor reductions in the FOI within a large-scale MDA schistosomiasis morbidity control programme in sub-Saharan Africa. The results indicate that the Schistosomiasis Control Initiative, as a model for other MDA programmes, is likely exerting a significant ancillary impact on reducing transmission within the community, and may provide health benefits to those who do not receive treatment. The results obtained will have implications for evaluating the cost-effectiveness of schistosomiasis control programmes and the design of monitoring and evaluation approaches in general.

Show MeSH
Related in: MedlinePlus