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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

Categories of infection intensity in untreated 6yr olds.The comparison between model outputs (dashed lines) and observed values (solid lines) with respect to the frequency of infection intensity categories in previously untreated 6-yr olds entering the cohort each year: A) high intensity areas; B) medium intensity areas; C) low intensity areas, as defined in Figure 1. BL, F1, F2 and F3 as in Figure 3. Red lines indicate heavy intensity of infection (≥400 epg), and blue lines indicate moderate intensity of infection (100–399 epg). Note the differences in the y-axis scales between the three endemicity levels.
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pntd-0000897-g006: Categories of infection intensity in untreated 6yr olds.The comparison between model outputs (dashed lines) and observed values (solid lines) with respect to the frequency of infection intensity categories in previously untreated 6-yr olds entering the cohort each year: A) high intensity areas; B) medium intensity areas; C) low intensity areas, as defined in Figure 1. BL, F1, F2 and F3 as in Figure 3. Red lines indicate heavy intensity of infection (≥400 epg), and blue lines indicate moderate intensity of infection (100–399 epg). Note the differences in the y-axis scales between the three endemicity levels.

Mentions: Figures 5 and 6 compare with model predictions and for untreated 6-year olds, the observed parasite load and the percentage of children within each intensity category, respectively. There is a statistically significant reduction in infection intensity (P<0.001) in the 6-year olds between baseline and follow-up year 2 (F2) in areas which were classified as of high intensity at baseline, and non-significant declines for moderate (P = 0.324) and low intensity areas (P = 0.142). Conversely, the intensity of infection in 6-year old children is higher at F3 than at F2 in both the high (P = 0.051) and low (P = 0.093) intensity schools. Such a result may be interpreted as a reduction in population MDA coverage in the last round of treatment. However, our analysis indicates that this was not reflected in the rate of parasite reinfection in older age groups (Table 2). In high intensity areas the observed data and predicted outcomes match relatively well though in medium and low intensity areas the model over- and underestimates parasite intensity respectively. We derive a reasonable fit to the data for the change in frequency of heavy and moderate infection categories (light and non-infected are omitted for clarity).


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)

Categories of infection intensity in untreated 6yr olds.The comparison between model outputs (dashed lines) and observed values (solid lines) with respect to the frequency of infection intensity categories in previously untreated 6-yr olds entering the cohort each year: A) high intensity areas; B) medium intensity areas; C) low intensity areas, as defined in Figure 1. BL, F1, F2 and F3 as in Figure 3. Red lines indicate heavy intensity of infection (≥400 epg), and blue lines indicate moderate intensity of infection (100–399 epg). Note the differences in the y-axis scales between the three endemicity levels.
© Copyright Policy
Related In: Results  -  Collection

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

pntd-0000897-g006: Categories of infection intensity in untreated 6yr olds.The comparison between model outputs (dashed lines) and observed values (solid lines) with respect to the frequency of infection intensity categories in previously untreated 6-yr olds entering the cohort each year: A) high intensity areas; B) medium intensity areas; C) low intensity areas, as defined in Figure 1. BL, F1, F2 and F3 as in Figure 3. Red lines indicate heavy intensity of infection (≥400 epg), and blue lines indicate moderate intensity of infection (100–399 epg). Note the differences in the y-axis scales between the three endemicity levels.
Mentions: Figures 5 and 6 compare with model predictions and for untreated 6-year olds, the observed parasite load and the percentage of children within each intensity category, respectively. There is a statistically significant reduction in infection intensity (P<0.001) in the 6-year olds between baseline and follow-up year 2 (F2) in areas which were classified as of high intensity at baseline, and non-significant declines for moderate (P = 0.324) and low intensity areas (P = 0.142). Conversely, the intensity of infection in 6-year old children is higher at F3 than at F2 in both the high (P = 0.051) and low (P = 0.093) intensity schools. Such a result may be interpreted as a reduction in population MDA coverage in the last round of treatment. However, our analysis indicates that this was not reflected in the rate of parasite reinfection in older age groups (Table 2). In high intensity areas the observed data and predicted outcomes match relatively well though in medium and low intensity areas the model over- and underestimates parasite intensity respectively. We derive a reasonable fit to the data for the change in frequency of heavy and moderate infection categories (light and non-infected are omitted for clarity).

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