A New Furunculosis Challenge Method for Evaluation of Vaccine Efficacy in Rainbow Trout

Abstract

Experimental infection of fish for vaccine efficacy studies is associated with several limitations. Administration of live bacteria with the purpose of causing disease in fish can be performed by co-habitation, immersion or injection. We have developed a new Aeromonas salmonicida challenge method for rainbow trout and have applied it for evaluation of furunculosis vaccine efficacy. The method reveals development of systemic immunity in fish as live bacteria are introduced in the tail fin epidermis distant from the vaccine injection site (peritoneal cavity). This method seeks to mimic natural infection in fish farms where tail biting and therefore bacterial exposure to tail fin ulcers is widespread. By use of a multi-needle device ten epidermal perforations were introduced in the dorsal part of the tail fin of anaesthetized rainbow trout (vaccinated or naive). Subsequently 100 µL (3.4 × 10 8 colony-forming units (CFU) mL −1) of a 48 hour culture of Aeromonas salmonicida subsp. salmonicida strain 090710-1/23 was placed at the perforation site for 60 sec whereafter fish were allowed to regain consciousness in clean freshwater. Immunohistochemistry and scanning electron microscopy illustrated the spread of bacteria from the injection site. Classical furunculosis symptoms associated with a high morbidity rate were observed in control fish whereas vaccinated fish exhibited a significantly higher survival.

Experimental anal infection of rainbow trout with Flavobacterium psychrophilum: A novel challenge model

“…injection (1.4 × 10 7 cfu/fish), (b) anal intubation (1.4 × 10 7 cfu/fish), (c) co‐habitation challenge (using 10 infected donor fish [i.p. injected 1.4 × 10 7 cfu/fish] kept with 15 recipient fish), (d) pre‐exposure to hydrogen peroxide (H 2 O 2 ) 200 mg/L for 1 hr before bacterial bath exposure (1.3 × 10 8 cfu/ml for 1 hr), (e) tail‐fin injury using a multi‐puncture device (Marana et al., ) before 1 hr bacterial bath exposure as described above, (f) bath exposure (1.3 × 10 8 cfu/ml) for 1 hr without any external intervention, (g) i.p. injection using sterile broth (uninfected control), (h) anal intubation using sterile broth (uninfected control).…”

“…injected fish was probably due to accidental injury of internal organs as no infection was recorded in this group. In the present study, we applied a tail‐fin puncture method which was successfully tested and established against Aeromonas salmonicida challenge (Marana et al., ), but when using this method for F. psychrophilum merely 6% mortality (in only one tank) was achieved. The anal intubation method produced mortality (43%) comparable to that of i.p.…”