Observed reductions in Schistosoma mansoni transmission from large-scale administration of praziquantel in Uganda: a mathematical modelling study.
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
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.
Schistosomiasis Control Initiative, Imperial College London, London, United Kingdom. michael.french05@imperial.ac.uk
Michael D
MD
French
Thomas S
TS
Churcher
Manoj
M
Gambhir
Alan
A
Fenwick
Joanne P
JP
Webster
Narcis B
NB
Kabatereine
Maria-Gloria
MG
Basáñez
D000293:Adolescent; D000328:Adult; D000818:Animals; D000871:Anthelmintics / Q000008:administration & dosage*; D002648:Child; D002675:Child, Preschool; D005243:Feces / Q000469:parasitology; D005260:Female; D006801:Humans; D007223:Infant; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D008962:Models, Theoretical; D011223:Praziquantel / Q000008:administration & dosage*; D012550:Schistosoma mansoni / Q000187:drug effects / Q000502:physiology; D012555:Schistosomiasis mansoni / Q000188:drug therapy* / Q000469:parasitology / Q000517:prevention & control / Q000635:transmission*; D014454:Uganda; D055815:Young Adult
D000871:Anthelmintics; D011223:Praziquantel