Furunculosis Injection Model for Drug Efficacy Testing of Seawater-Adapted Atlantic Salmon

Abstract

We describe an injection model for creating furunculosis, caused by Aeromonas salmonicida, in seawater-adapted Atlantic salmon Salnw salar and for testing the efficacy of chemotherapeutants. An injection model was most appropriate for chemotherapcutant studies. Isolate selection was based on determination of drug resistance and the pathogenicity of the isolate, both of which can vary widely. Fish were handled without anesthesia with minimal handling stress; their feeding behavior was normal. Preliminary challenge trials demonstrated highly variable pathogenicity for different isolates of A. salmonicida. In the main four-dose challenge of 30. 90. 300, and 900 bacteria per fish, cumulative 16-d mortality rates ranged from 28% to 38%. Onset of deaths was earlier for the two higher doses, and these doses resulted in greater cumulative mortality than did the lower two doses. Power analysis of the data showed that with a tive-replicale study, a 12.1% difference in cumulative mortality rate between the control and treatment would be required to show statistical significance at the P = 0.05 level and that with four-, three-, and two-replicate studies, cumulative mortality rate differences between treatment and control of 13.6%, 15.7%, and 19.1%, respectively, would be required. The data generated can be used to define the parameters for definitive challenges used to establish drug dose-efficacy relationships.

Efficacy of orally administered oxolinic acid and Vetoquinol, an oxolinic acid ester, for the treatment of furunculosis in Atlantic salmon Salmo salar held in seawater

“…To test the efficacy of chemotherapeutants, different challenge models have been used to experimentally induce furunculosis in fish (Elston et al 1995, Samuelsen et al 1997, Nordmo et al 1998. To mimic natural infection the disease was induced in this investigation by introduction of cohabitant fish previously infected by a n intraperitoneal injection with the pathogen.…”

Efficacy of Orally Administered Difloxacin for the Treatment of Furunculosis in Atlantic Salmon Held in Seawater

“…Difloxacin is a prom-scribed b * Elslon el aL (I995 ' lnis issue) ' ising fluoroquinolone that may have therapeutic use for control of diseases of coldwater fish such Methods as Atlantic salmon Salmo salar. The bioavailability Experimental fish.-Juvenile Atlantic salmon of difloxacin to Atlantic salmon in seawater and were obtained, maintained, and monitored as defresh water was recently tested (Elston et al 1994), scribed by Elston et al (1995), who also estab- u Color codes were assigned by Ronald Hardy during teed preparation it) provide a blind feed administration procedure for the experiment. The identity of the coded feed was not provided to the investigators until after the completion of the in life phase.…”

“…Aeromonas salwonicida isolates.-The isolate of Aeromonas sahnonicida (designated B-2) used in this study was maintained, cultured, and quantified as descrihed hy Elston et al (1995). Several isolates were initially screened tor their sensitivity to difloxacin at concentrations less than 1 jxg/L.…”

“…The challenge dose was cultured and later verified to equal 327 organisms/fish in trial 1 and 284 organisms/fish in trial 2. Fish were injected intramuscularly, as described previously (Elston et al 1995), and placed into the experimental tank. The bacteria were injected within 3.5 h of harvest of the bacteriological cultures in both trials.…”