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.