L.-H. Johansen & A.-I. Sommer, Fiskeriforskning, Tromsø, Norway
Challenge models are important tools in fish health research. Development of vaccines or other prophylactic treatment and studies of effects of intensive rearing conditions are examples of areas where challenge models are essential. In nature the interaction between the host, the pathogen and the environment is decisive for the outcome of an infection. Thus, factors that need to be considered to obtain a reliable model with adequate mortality levels are:
-The susceptibility of the host to the pathogen – often defined by host age, size and genetic background
-The virulence of the pathogen – its ability to cause mortality and the concentration needed to give required mortality levels.
-Environmental factors – temperature, fish density in the tank, water flow, etc.
-Procedures of infection - bath or injection, duration time, number of tanks, number of fish in each group.
Also, when designing a new model it may be necessary to compromise between scientific reliability, statistical significance, ethical considerations and cost.
At Fiskeriforskning we have designed an IPN (infectious pancreatic necrosis) virus challenge model in Atlantic salmon smolts, initially as a research tool. Later it proved to be useful for testing efficacy of vaccines and thus have contributed to the development of more efficient vaccines. The making and maintenance of this model is a good example of all the challenges one meets when designing models for infectious diseases in general. Results will be presented from experiments conducted during its development and from research projects where the model has been used.