A deterministic model for the dynamics of furunculosis in chinook salmon Oncorhynchus tshawytscha

Studies were undertaken to determine the parameters of transmission of Aeromonas salmonicida in chinook salmon Oncorhynchus tshawytscha, and to develop a deterministic model of the dynamics of experimental furunculosis. For determination of disease transmission coefficient (beta), disease-related mortality rate (alpha) and natural mortality rate (gamma), fish in 70 tanks (approximately 42 fish tank(-1)) were each exposed to a single infectious donor fish, 7 tanks were randomly selected daily and all individuals were examined for the presence of A. salmonicida in the kidney. The proportion of susceptible (S), infected (I) and removed (R, dead) individuals were determined daily. The parameters beta, alpha, gamma, reproductive ratio (R0) and threshold density were estimated to be 0.0214 infected ind. d(-1), 0.29 infected ind. d(-1), 0.00015 ind. d(-1), 3.23 and 13.56 ind., respectively. Using these parameters, a deterministic disease model of A. salmonicida infection as a cause of furunculosis was constructed. The net rate at which new individuals became infected (the incidence rate) per unit time was proportional to S x I x beta. The model-produced data for S were significantly associated with experimental data (r2 = 0.92). In brief, a simple SIR (susceptible-infected-removed) model was successfully utilized to simulate observed data