Estimating and comparing the risk of infectious salmon Anaemia virus (ISAv) spread between Atlantic salmon farms in southwestern New Brunswick

Principal Investigator: Raju Gautam
Co-Investigators: Kim Klotins (CFIA), Ian Gardner, Crawford Revie, & Raphael Vanderstichel

Atlantic Canada has previously experienced outbreaks of infectious salmon anaemia virus (ISAv). Should it reoccur, a well-planned response strategy would help control spread of the virus. Although disease modelling and simulation have been used to guide preparedness planning for diseases of terrestrial animals, such tools are lacking for the marine environment. A major challenge in adapting tools developed for terrestrial animals to aquatic animals is related to measurement of distances between farms. In terrestrial systems, the distance between farms is often measured using Euclidian (straight line) distance, while distances in aquatic systems are measured with seaway distance, which may or may not be a straight line. Modelling tools developed for terrestrial systems have not yet been systematically evaluated for use in the marine environment.

The main goal of this project was to estimate and compare risk of ISAv spread using seaway distances and adjusted seaway distances (which include water movement information) for each farm location. We compared models of the spread of a hypothetical introduction of ISAv to a farm in the Bay of Fundy area, New Brunswick. To assess model accuracy, the 5 farms predicted to be at highest risk of infection were compared to farms that became infected in the next time period, using outbreak data for that area from 2004. Overall accuracy of the seaway distance-based model was 65.8%, compared to 57.5% for the adjusted seaway distance-based method, and the accuracy of prediction for virus spread at individual time points ranged from 0% to 100%. This project will resume in September 2017 and try to explain why the adjusted seaway distance model predicted disease spread with lower accuracy than the model using unadjusted seaway distance.