Event Abstract

Back to Event

Risk factors for treatment failure in antibiotic treatments against Piscirickettsiosis in farmed Atlantic salmon in Chile

Derek Price1*, Henrik Stryhn1, Javier Sanchez1, Alfredo Tello2, Rolando Ibarra2 and Sophie St-Hilaire1
  • 1 University of Prince Edward Island, Department of Health Management, Atlantic Veterinary College, Canada
  • 2 Instituto Tecnológico del Salmón, Intesal-SalmonChile, Chile

Piscirickettsiosis remains the most prevalent infectious disease in Chilean salmon farming (Sernapesca 2015a), and treatments against Piscirickettsia salmonis, the causative agent of the disease, accounted for 90% of the antimicrobials used in the aquaculture industry in 2014 (Sernapesca 2015b). A recent study on the susceptibility of P. salmonis to the antimicrobials oxytetracycline and florfenicol, found only a few resistant isolates (Henríquez et al. 2016), which is not consistent with the high proportion of treatments reported as unsuccessful by farmers. This difference suggests that factors other than resistance may be driving treatment failures under field conditions. Using retrospective treatment and weekly production data, from 2014 pens on 118 farms from 14 companies, the objective of this study was to assess the role of fish weight, water temperature, and pre-treatment mortality on the effectiveness of antimicrobial treatments against piscirickettsiosis. We defined failure when the average weekly mortality in a 3-week period post-treatment was above 0.1%, a cut-off consistent with other studies (Rees et al. 2014; Jakob et al. 2014) and within the baseline mortality level observed in Chile during our study period. We modeled the probability of failure for each pen using a mixed-effects logistic regression model with random effects for company and farm. We found that as pre-treatment mortality increased so did the probability of treatment failure. The relationship between pre-treatment mortality levels and probability of treatment failure may be related to the stage of the disease in the population, assuming pens of fish with higher mortalities had more animals infected with the pathogen, and the pathogen load in the tissues of individual fish was higher. We also found that when using florfenicol, weight was negatively associated with treatment outcome. As fish grow, feeding frequency is usually reduced to minimize competition and keep feed conversion rates low. Maintaining therapeutic levels of antibiotics while reducing feeding frequency depends on the half-life of the product. Our results suggest that under these husbandry conditions, maintaining therapeutic tissue concentrations would be most difficult for florfenicol, as this product has a short half-life. Preliminary examination of fish treated with florfenicol suggests a wide range of tissue concentrations within populations with a high proportion of fish below the epidemiological cut-off values for Chilean isolates described by Henriquez et al 2015. Our results highlight the importance of early detection and timely treatment, and explore the potential relationship between pharmacokinetic properties of antimicrobials and their role in treatment success.

Acknowledgements

This research was funded by the Canada Excellence Research Chair Program. We thank Intesal-SalmonChile for the insightful discussions and providing access to Industry data.

References

Henríquez, P., Kaiser, M., Bohle, H., Bustos, P., and Mancilla, M. (2016) Comprehensive Antibiotic Susceptibility Profiling of Chilean Piscirickettsia Salmonis Field Isolates Journal of Fish Diseases 4:441–48. doi:10.1111/jfd.12427.
Jakob, E., Stryhn, H., Yu, j., Medina, M.H., Rees, E.E., Sanchez, J., and St-Hilaire, S. (2014) Epidemiology of Piscirickettsiosis on Selected Atlantic Salmon (Salmo Salar) and Rainbow Trout (Oncorhynchus Mykiss) Salt Water Aquaculture Farms in Chile. Aquaculture 433. doi:10.1016/j.aquaculture.2014.06.018.
Rees, E.E., Ibarra, R., Medina, M., Sanchez, J., Jakob, E., Vanderstichel, R., and St-Hilaire, S. (2014) Transmission of Piscirickettsia Salmonis Among Salt Water Salmonid Farms in Chile. Aquaculture 428: 189–94. doi:10.1016/j.aquaculture.2014.03.031.
Sernapesca (2015a) Informe Sanitario de Salmonicultura En Centros Marinos Año 2015. Departamento de salud animal, Servicio Nacional de Pesca y Acuicultura.
Sernapesca (2015b) Informe Sobre Uso de Antimicrobianos En La Salmonicultura Nacional. Departamento de salud animal, Servicio Nacional de Pesca y Acuicultura.

Keywords: Piscirickettsia salmonis, Pisciricketsiosis, Salmonid rickettsial septicemia, Treatment effectivenes, Atlantic salmon

Conference: AquaEpi I - 2016, Oslo, Norway, 20 Sep - 22 Sep, 2016.

Presentation Type: Oral

Topic: Aquatic Animal Epidemiology

Citation: Price D, Stryhn H, Sanchez J, Tello A, Ibarra R and St-Hilaire S (2016). Risk factors for treatment failure in antibiotic treatments against Piscirickettsiosis in farmed Atlantic salmon in Chile. Front. Vet. Sci. Conference Abstract: AquaEpi I - 2016. doi: 10.3389/conf.FVETS.2016.02.00051

Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters.

The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated.

Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed.

For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions.

Received: 29 Apr 2016; Published Online: 14 Sep 2016.

* Correspondence: Mr. Derek Price, University of Prince Edward Island, Department of Health Management, Atlantic Veterinary College, Charlottetown, Prince Edward Island, C1A 4P3, Canada, dprice@upei.ca