Prediction of schistosome cercarial shedding with a physiological - time model.

While making longitudinal observations on schistosome cercarial shedding, Pitchford and Visser found that there is an annual fluctuation in the minimum time for cercarial development, which is apparently related to temperature (1). Schistosome control strategy could be designed to take advantage of this fluctuation if it were predictable. Inspired by the successes of physiological time models ('heat-unit models') in predicting life-stage durations of various agricultural pests (2,3), we have developed a model of this type for the schistosomes. This model fits the data of Pitchford and Visser quite well. Coupled with recent temperature history and short term temperature forecast, it could be a useful tool for predicting the onset of cercarial shedding.