Transmission of Piscirickettsia salmonis among salt water salmonid farms in Chile

Salmon Rickettsia Syndrome (SRS), also known as Salmon Rickettsia Septicemia, caused by Piscirickettsia salmonis is the most common bacterial disease in the Chilean salmon aquaculture industry. The epidemiology of this pathogen is relatively unknown. Using the Chilean salmon aquaculture industry monthly diagnostic data collected between January 2009 and December 2012, we assessed the spatial and environmental factors associated with the reporting of SRS on Atlantic salmon, coho salmon, and rainbow trout farms. Crops of fish were on average 60% likely to report SRS during our study time period. The probability of a farm reporting SRS was positively associated with temperature, time in salt water, and the number of SRS infected neighbors. The distance effect from infected neighboring farms that best fit the model for predicting SRS on a farm varied by species but ranged between 7.5 and 10 km. Our study suggests reducing disease on farms will not only benefit the producer but also reduce the probability that P. salmonis is transferred to neighboring farms.