Brachylaime microti: A mechanistic simulation model of the parasite, its intermediate snail host, Oreohelix strigosa, and its definitive rodent hosts, Peromyscus maniculatus and Microtus montanus

Abstract

A mechanistic simulation model was developed to predict the responses of parasite populations to variation in host population levels and environmental conditions. The parasite life cycle selected for the model was that of Brachylaime microti, a trematode utilizing a terrestrial snail, Oreohelix strigosa, as intermediate host, and rodents, Peromyscus maniculatus and Microtus montanus, as definitive hosts. A mechanistic compartment-flow representation was employed in modeling the system. The system parameters to be predicted were represented by compartment levels, with flows between compartments governed by rate processes, using mathematical functions to simulate the biological mechanisms involved. The compartments were the levels in terms of numbers of each parasite life stage, including sporocyst, cercariae, metacercariae, adult, and egg. The rate processes included infection, grazing, nutrition, reproduction, and mortality. The external driving variables were the weather parameters and host population levels. A system of difference equations was developed to to describe these processes for computer simulation. The model was tested statistically, using a confidence interval approach to compare actual field data with model predictions. The model passed this statistical test and tests of weather stress, indicating that it was consistent with observations and knowledge of the system.