Schistosomiasis control in Mali – or not
Geostatistical maps are increasingly being used to plan neglected tropical disease control programmes. A decade after the conclusion of a schistosomiasis control program in Mali, prevalence of the disease has regressed to pre-intervention levels. New research finds that clusters of schistosomiasis infections occur generally in the same areas ten years after the end of a donor-funded control program, conducted between 1982 and 1992.
Schistosomiasis is a parasitic disease caused by several species of fluke of the genus Schistosoma. Although it has a low mortality rate, schistosomiasis often is a chronic illness that can damage internal organs and, in children, impair growth and cognitive development. Mali is one of the first countries in sub-Saharan Africa to have initiated a national schistosomiasis control program. Lack of government funding curtailed the program’s activities after 1998, until a new program, backed by the Schistosomiasis Control Initiative, began in 2004.
The authors undertook a comparative study of the spatial distribution of schistosomiasis in Mali between 1984-1989 and 2004-2006. They show that the spatial distribution of schistosomiasis was similar in both time periods, even in the face of large-scale control program based on mass distribution of anti-parasitic drugs. Long-term stability in the spatial distribution of schistosomiasis means that reviewing historic data can provide a useful, initial source of evidence for planning targeted contemporary control program. However, if these control program are to have a sustainable impact on the burden of schistosomiasis they must be delivered over a very long time period, or supplementary methods need to be implemented, such as improvement in water sanitation and hygiene.
This work has two main implications: that historic data can be used, in the first instance, to plan contemporary control programmes due to the stability of the spatial distribution of schistosomiasis; and that a decade of donor-funded mass distribution of praziquantel has had no discernable impact on the burden of schistosomiasis in subsequent generations of Malians, probably due to rapid reinfection.
A Comparative Study of the Spatial Distribution of Schistosomiasis in Mali in 1984–1989 and 2004–2006. 2009 PLoS Negl Trop Dis 3(5): e431
We investigated changes in the spatial distribution of schistosomiasis in Mali following a decade of donorfunded control and a further 12 years without control. National pre-intervention cross-sectional schistosomiasis surveys were conducted in Mali in 1984–1989 (in communities) and again in 2004–2006 (in schools). Bayesian geostatistical models were built separately for each time period and on the datasets combined across time periods. In the former, data from one period were used to predict prevalence of schistosome infections for the other period, and in the latter, the models were used to determine whether spatial autocorrelation and covariate effects were consistent across periods. Schistosoma haematobium prevalence was 25.7% in 1984–1989 and 38.3% in 2004–2006; S. mansoni prevalence was 7.4% in 1984–1989 and 6.7% in 2004–2006 (note the models showed no significant difference in mean prevalence of either infection between time periods). Prevalence of both infections showed a focal spatial pattern and negative associations with distance from perennial waterbodies, which was consistent across time periods. Spatial models developed using 1984–1989 data were able to predict the distributions of both schistosome species in 2004–2006 (area under the receiver operating characteristic curve was typically >0.7) and vice versa. A decade after the apparently successful conclusion of a donor-funded schistosomiasis control programme from 1982–1992, national prevalence of schistosomiasis had rebounded to pre-intervention levels. Clusters of schistosome infections occurred in generally the same areas accross time periods, although the precise locations varied. To achieve long-term control, it is essential to plan for sustainability of ongoing interventions, including stengthening endemic country health systems.
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Tags: Africa, Biology, Environment, Health, Medicine, Microbiology, Parasitology, Schistosomiasis, Science
