Prototype of simulation models for epizootics in domestic animals

Based on the Reed-Frost model (Model I), the authors conducted computer simulation of an epizootic model (Model II) constructed on the assumption that any infected animal in a group, after a given time-period of infectivity, would be removed from the group at the beginning of the next time-period. Models I and II were simulated 100 times for each of the different conditions, viz. the initial size of group, 100 and 1,000, the five steps of contact rate or contact size, and the five more steps of contact rate for the group of 1,000 animals in Model I. From the results obtained, it is believed that as a constant parameter, contact size may be preferably used instead of contact rate in these models. Model II mostly gave higher morbidities than Model I, and earlier termination of epizootics, except the simulation with the smallest contact size. This fact may be due to the effect of herd immunity involved only in Model I. The long duration of epizootic was demonstrated in two of the 100 simulations of Model II with 1,000 individuals and contact size 1. This is characteristic of probabilistic models which are really instructive to studying the flow of epizootic.