How improvements to drug effectiveness impact mass drug administration for control and elimination of schistosomiasis

Objectives

The study investigated the impact of drug profile improvements to the current practice of using praziquantel (PZQ) in MDA, employing an individual based stochastic mathematical model of the transmission and mass drug treatment of S. mansoni and S. haematobium.

Methods

Using a stochastic individual based model developed at Imperial College London (the Imperial model) that is based on the deterministic model that has been described in previous publications. The study also replicated some of the simulations with the SCHISTOX model, developed at the University of Oxford. These two models are similar but differ in how egg production is modelled: SCHISTOX assumes that the number of eggs produced is proportional to the number of worm pairs, whereas the Imperial model assumes egg production is density-dependent so that the higher the burden of infection, the less productive each individual worm is.

Results

Study results show that increased efficacy against juvenile worms can only result in modest benefits, but the development of a new drug formulation with higher efficacy against adult worms or long-lasting efficacy would create an improvement to the community impact over the currently used formulation.

Conclusions

The study findings reveal that with good coverage, an improved drug efficacy is best at reducing prevalence and achieving interruption of transmission. However, when MDA quality is compromised due to low coverage, infrequent treatment or high rates of non-adherence, then a long-lasting efficacy performs best. There is only a modest benefit of improved drug efficacy against juvenile schistosomes. These results highlight the importance of providing frequent treatment at high coverage levels in the population and inform future drug development aims.