Risk Factors Associated With Tenacibaculosis-Related Mortality in Farmed Salmon in Chile From 2018 to 2021

Tenacibaculosis, caused by bacteria of the genus Tenacibaculum (Family Flavobacteriaceae, Phylum Bacteroidota), has emerged as a major health concern in Chilean marine salmon farming and is among the leading causes of mortality in recent years. We conducted descriptive epidemiological analyses, time-series decomposition, and survival analysis, together with a case-control study of 1192 Chilean marine production cycles (2018-2021), using official surveillance data. Of these, 777 cycles (65.2%) reported mortality associated with tenacibaculosis. The disease affects Atlantic salmon (Salmo salar), Coho salmon (Oncorhynchus kisutch), and rainbow trout (O. mykiss), and is widely distributed across the main marine farming regions (Los Lagos, Aysén, and Magallanes). Mortality rates exhibited a clear seasonal pattern, occurring predominantly during periods of low water temperature (6°C-12.7°C, depending on the region), with substantially higher mortality compared to warmer periods, indicating a strong temperature-associated effect. The median time from stocking to the onset of tenacibaculosis-related mortalities was shortest in Magallanes (9 weeks), followed by Aysén (13 weeks) and Los Lagos (26 weeks). By species, onset occurred earlier in Atlantic salmon (12 weeks) and rainbow trout (15 weeks) than in Coho salmon (33 weeks). Median cumulative mortality per production cycle varied by species and region. For Atlantic salmon, median values were 0.09% in Los Lagos, 0.27% in Aysén, and 0.14% in Magallanes. For rainbow trout, the corresponding values were 0.01%, 0.04%, and 0.31%, while for Coho salmon they were 0.003%, 0.01%, and 0.003%, respectively. Logistic regression was used to assess risk factors for tenacibaculosis reporting. Univariate logistic regressions identified significant associations with region, species, mechanical injuries, piscirickettsiosis, and caligidosis (p < 0.05). In the multivariable model, infestation with Caligus rogercresseyi (Odds Ratio [OR] = 3.23; 95% Confidence Interval [CI]: 1.77-6.02) and Atlantic salmon farming in Aysén (OR = 5.41; 95% CI: 1.32-36.83) remained significantly associated with tenacibaculosis. These findings provide new insights into the epidemiology and risk factors of tenacibaculosis in Chilean salmon farming, informing strategies for disease prevention and management.