Comparison of different challenge methods to evaluate the efficacy of furunculosis vaccines in Atlantic salmon, Salmo salar L.

Abstract

Four challenge methods, intraperitoneal (i.p.) and intramuscular (i.m.) inoculation, bath and cohabitation exposure, were evaluated as methods for testing the efficacy of furunculosis vaccines in Atlantic salmon, Salmo salar L. Groups of fish vaccinated with one of two different vaccines containing aluminium phosphate or animal/vegetable oil as an adjuvant were challenged with Aeromonas salmonicida 6 and 12 weeks after vaccination. Relative per cent survival (RPS) was calculated daily during a 3‐week observation period post‐challenge. A large variation in protection measured by RPS, both between methods and between different time points for each method, was found. Towards the end of the observation period, RPS tended to be similar in the i.p. and cohabitation challenge groups. A high degree of protection was demonstrated for the oil adjuvanted vaccine. The i.m. challenge produced very low RPS numbers for both vaccines, but this was most marked for the aluminium‐phosphate‐adjuvanted vaccine. The bath exposure resulted in RPS values intermediate to the cohabitation and injection methods. The study also demonstrated that, after i.p. and i.m. challenges, the initial peak mortality caused by the inoculation was followed by a secondary increase in mortality, probably because of shedding of bacteria into the water during the first mortality phase and hence contributing to a superinfection state.

Contribution of the type III secretion system (TTSS) to virulence of Aeromonas salmonicida subsp. salmonicida

“…However, the challenge data suggest strongly that the TTSS of A. salmonicida is required for host invasion. By immersion, a route of administration that requires host invasion to establish an overt disease state (Cardella & Eimers, 1990;Nordmo & Ramsted, 1997), an inactive secretory complex completely abolished virulence. The level of overt disease caused by DaopH was significantly reduced and DaexT was also attenuated.…”

A vaccination and challenge model using calcein marked fish

“…Nordmo [1,27] reviewed the strengths and weakness of different challenge methods used to determine the efficacy of fish vaccines. Immersion and cohabitation routes were considered the challenge methods that most closely mimic natural routes of infection [28].…”

“…Immersion and cohabitation routes were considered the challenge methods that most closely mimic natural routes of infection [28]. However, Nordmo [1,27] indicated that ip challenge was a reproducible and reliable means for the determination of vaccine efficacy. In addition, the ip route ensures that each individual fish receives a uniform challenge; however, it is generally considered to be the least natural route of infection, unless the fish are subject to skin puncture by infected fish [1,27].…”

“…However, Nordmo [1,27] indicated that ip challenge was a reproducible and reliable means for the determination of vaccine efficacy. In addition, the ip route ensures that each individual fish receives a uniform challenge; however, it is generally considered to be the least natural route of infection, unless the fish are subject to skin puncture by infected fish [1,27]. Nordmo [1] also suggested that ip injection is acceptable where it is the primary cause of mortality (i.e., no secondary peaks of mortality caused by waterborne infection).…”

Adjuvant activities of aVibrio salmonicidabacterin on T-dependent and T-independent antigens in rainbow trout (Oncorhynchus mykiss)

“…V. salmonicida (VI 94/09/ 550) was grown in brain heart infusion broth (Difco, U.S.A.) containing 2% NaCl at 15 C, until the cell concentration reached 10 8 ml 1 , measured by a photometric method described by Nordmo & Ramstad (1997). The culture was inactivated with 0·5% v/v formalin (37%), and is henceforth referred to as V. salmonicida bacterin.…”