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Epidemiology of amoebic gill disease

Douglas-Helders, Greetje Marianne 2002 , 'Epidemiology of amoebic gill disease', PhD thesis, University of Tasmania.

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Amoebic gill disease (AGD) is the main disease affecting the salmon industry in
Australia, however inadequate information is available on the epidemiology of
amoebic gill disease (AGD) and the biology of the pathogen, Neoparamoeba
pemaquidensis (Page, 1987). Thus far no convenient mass screening test was
available. In this project a pathogen specific and non-lethal dot blot test was
developed and validated against indirect fluorescence antibody testing (IFAT), the
'gold standard'. The agreement between the 300 paired gill mucus samples that
were analysed using both tests was high, with a corrected kappa value of 0.88. The
overall aim of this project was to investigate distributions and seasonal patterns of
the pathogen, identify risk factors for the disease and reservoirs of N.
pemaquidensis, and develop and review husbandry methods in order to reduce
AGD prevalence.
Results of an infection trial implied that transmission of AGD infections in the field
do not only occur from fish to fish, but also from water to fish. Therefore
distribution of paramoebae in the water column and seasonal patterns were
investigated. The spatial and temporal distribution of paramoebae was determined
using the dot blot test and most probable number techniques for the identification
and quantification respectively. Associations between paramoebae densities and
environmental conditions were also explored.
Potential reservoirs were investigated in both field and laboratory trials. In a
laboratory study it was determined that dead AGD infected fish may be a reservoir
of N. pemaquidensis when left in sea cages. In the laboratory trial, N.
pemaquidensis remained on infected gills for at least 30 hours after death of the host, and these protozoa from dead infected fish could colonise gills of previously
uninfected dead fish. This would potentially increase the bio-burden of N.
pemaquidensis on infected farms. AGD was not detected in wild fish and wild fish
did not seem to be a reservoir of the pathogen.
Five different husbandry options were evaluated in extensive field trials with the
aim to minimise the impact of AGD. Three of the husbandry options seemed
beneficial in reducing either cost due to the disease and/or AGD prevalence on
Tasmanian salmon farms. All three options could easily be incorporated into
existing management plans.

Item Type: Thesis - PhD
Authors/Creators:Douglas-Helders, Greetje Marianne
Keywords: Neoparamoeba pemaquidensis, Fishes, Paramoebidae
Copyright Holders: The Author
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Copyright 2002 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D )--University of Tasmania, 2002. Includes bibliographical references

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