Seasonality in live fish movements and its effects on epidemic dynamics

Abstract

Live fish movements between salmon farms risk spreading pathogens, and movements between freshwater farms (FW–FW) or from freshwater to seawater (FW–SW) show clear seasonality. In this study, we quantify the effects of seasonality of live fish movements on epidemic dynamics, using a network model populated with data from live fish movements between Scottish salmon farms from 2002 to 2004. We used three types of networks: A) timing and pair-wise movements between farms were as observed; B) as network A, but with a random reordering of FW–FW and FW–SW movements; and C) number of movements were kept the same as in the data, but connection between nodes was random. We compared the time-course of simulated epidemics in a stochastic model for all three networks. We showed that seasonality had the strongest effect in networks B and C, especially when local transmission was high, and this effect was stronger in SW farms compared with FW farms.