Discussion

There is clear empirical evidence that environmental conditions can influence Ascaris lumbricoides free-living stage development and host reinfection, but the impact of these difference on human infections, and public health intervention, is variable. A new model framework reflecting four key stages of the A. lumbricoides life cycle, incorporating the effects of rainfall and temperature, is used to describe the level of infection in the human population alongside the environmental egg dynamics. Using data from South Korea and Nigeria, we conclude that settings with extreme fluctuations in rainfall or temperature could exhibit strong seasonal transmission patterns that may be partially masked by the longevity of A. lumbricoides infections in hosts; we go on to demonstrate how seasonally timed mass drug administration (MDA) could impact the outcomes of control strategies. For the South Korean setting the results predict a comparative decrease of 74.5% in mean worm days (the number of days the average individual spends infected with worms across a 12 month period) between the best and worst MDA timings after four years of annual treatment. The model found so significant seasonal effect on MDA in the Nigerian setting due to a narrower annual temperature range and no evidence of rainfall dependence. Our results suggest that seasonal variation in egg survival and maturation could be exploited to maximise the impact of MDA in certain settings.