How does treatment coverage and proportion never treated influence the success of Schistosoma mansoni elimination as a public health problem by 2030?

BackgroundThe 2030 target for schistosomiasis is elimination as a public health problem (EPHP), achieved when the prevalence of heavy intensity infection among school-aged children (SAC) reduces to <1%. To achieve this, the new World Health Organization (WHO) guidelines recommend a broader target of population to include pre-school (pre-SAC) and adults. However, the probability of achieving EPHP should be expected to depend on patterns in repeated uptake of mass drug administration (MDA) by individuals. MethodsWe employed two individual-based stochastic models to evaluate the impact of school-based and community-wide treatment and calculated the number of rounds required to achieve EPHP for Schistosoma. mansoni by considering various levels of the population never treated (NT). We also considered two age intensity profiles, corresponding to a low and high burden of infection in adults. ResultsThe number of rounds needed to achieve this target depends on the baseline prevalence and the coverage used. For low and moderate transmission areas, EPHP can be achieved within seven years if NT [&le;]10% and NT <5%, respectively. In high transmission areas, community wide treatment with NT<1% is required to achieve EPHP. ConclusionsThe higher the intensity of transmission, and the lower the treatment coverage, the lower the acceptable value of NT becomes. Using more efficacious treatment regimens would permit NT values to be marginally higher. A balance between target treatment coverage and NT values may be an adequate treatment strategy depending on the epidemiological setting, but striving to increase coverage and/or minimise NT can shorten programme duration.