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[[Category:To Do - CABI]]
Also Known As – '''''AGD - Amoebiasis – Amoebic Gill Infection – Amoebosis - Paramoebiasis'''''
Caused By – ''Neoparamoeba pemaguidensis''
==Introduction==
Amoebic gill disease is caused by '''''Neoparamoeba pemaguidensis''''', the '''most important pathogenic amoeba in fish'''. The disease causes large economic losses in '''marine cultured salmonids'''.<ref> Munday, B. L., Zilberg, D., Findlay, V (2001) '''Gill disease of marine fish caused by infection with Neoparamoeba pemaquidensis'''. J Fish Diseases, 24(9):497-507</ref> It can also affect turbots.
==Distribution==
Tasmania, Asutralia, Ireland, France, North America and Spain suffer the most significant losses due to AGD.
Although small numbers of the amoeba have been found on the gills of wild fish, it is unknown if they can be source of infection in cage-cultured salmonids.
==Signalment==
'''Atlantic salmon and rainbow trout''' are most susceptible to disease.
Turbot, brown trout, bass, bream, sea urchins<ref> Jones, G. M., Scheibling, R. E (1985) '''Paramoeba sp. (Amoebida, Paramoebidae) as the possible causative agent of sea urchin mass mortality in Nova Scotia'''. J Parasitology, 71:559-565</ref> and crabs<ref> Johnson, P. T (1977) '''Paramoebiasis in the blue crab, Callinectes sapidus.''' J Invertebrate Pathology, 29(3):308-320</ref> can also be infected, causing morbidity and mortality.
The amoeba will also readily colonise severe injuries such as jellyfish stings, clubbed lamellae and necrotic gill syndrome lesions.
Clinical AGD is always associated with '''water temperatures of 12-20⁰ and high salinities of ≥32 ppt'''. <ref> Rodger, H. D., McArdle, J. F (1996) '''An outbreak of amoebic gill disease in Ireland'''. Veterinary Record, 139(14):348-349</ref> Amoeba numbers also rise in the Summer.
==Clinical Signs==
AGD causes '''mucus to build up on the gills''' of infected fish and '''hyperplasia of the gill tissues''' to occur. The '''secondary lamellae may fuse together'''. Fish often '''swim close to the surface and gulp air''' as they become dyspnoeic. '''Opercular movements will increase'''. They may swim '''belly upwards''' in the terminal stages. Diseased fish usually stop feeding become lethargic and '''mortalities''' are common.
==Diagnosis==
Finding ''N. pemaguidensisis'' not always pathological and it is important to distinguish in which cases it is the aetiological agent. The presence of '''multiple, typical mucoid patches on the gills''' is highly suggestive of AGD.
Wet mounts of gill tissue can be tested with '''Immunofluorescent Antibody Testing(IFAT), Quick Dip®'''<ref> Zilberg, D., Nowak, B., Carson, J., Wagner, T (1999) '''Simple gill smear staining for diagnosis of amoebic gill disease.''' Bulletin of the European Association of Fish Pathologists, 19(5):186-189</ref> and '''dot-blot techniques'''<ref>Douglas-Helders, M., Carson, J., Howard, T., Nowak, B (2001) '''Development and validation of a new dot blot test for the detection of Paramoeba pemaquidensis (Page) in fish'''. J Fish Diseases, 24(5):273-280</ref> which is used for mass screening.
Histologically, '''amoebae can be seen attaching to the gill epithelium''' with haematoxylin & eosin stain. '''PCR''' is also available.
On necropsy, multifocal patches of '''white to grey swollen gill tissue''' with excessive mucus associated is characteristic of AGD. This is particularly evident in the dorsal gill arches.<ref> Adams, M. B., Nowak, B. F (2001) '''Lesion distribution and structure in the gills of Atlantic salmon (Salmo salar L.) affected with amoebic gill disease'''. In: Battaglene SC, Cobcoft JM, eds. '''The First Scientific Conference of the Atlantic Salmon Subprogram Handbook.''' ''Hobart, Tasmania, Australia: CSIRO Marine Laboratories'', 28-29</ref> These changes tend to be more diffuse in rainbow trout than in salmon.
Histopathological features are similar in all species affected and feature essentially '''hyperplasia and hypertrophy of the gill epithelium'''.<ref>Zilberg, D., Munday, B. L (2000) '''Pathology of experimental amoebic gill disease in Atlantic salmon, Salmo salar L., and the effect of pre-maintenance of fish in sea water on the infection'''. J Fish Diseases, 23(6):401-407</ref> Gill '''lamellae are often fused and tissues spongiotic'''.
==Treatment==
'''Freshwater baths''' are the only proven therapy but are very stressful for the fish.
'''Chloramine, chlorine dioxide and levamisole''' have also been used.
==Control==
Lack of information about transmission and carriers of the disease has made control difficult to design and implement.
{{Learning
|flashcards = [[Amoebic Gill Disease Flashcards]]
}}
==References==
<references/>
Animal Health & Production Compendium, '''Amoebic Gill Disease datasheet''', accessed 07/07/2011 @ http://www.cabi.org/ahpc/
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