Download Gills from Atlantic salmon with experimentally induced amoebic gill

Ultrastructural examination of the host cellular response in the gills of Atlantic Salmon, Salmo
salar, with amoebic gill disease
Exotic/fish
Immunology/infectious disease
Vet Path 44:663-671 (’07)
Abstract. Gills from Atlantic salmon with experimentally induced amoebic gill disease (Neoparamoeba spp.) were
examined with transmission electron microscopy to assess pathology and host-cell responses. Amoebae were found
either on the surface epithelium or with pseudopodia extending deeply into invaginations of epithelial cells. The
amoebae had various densities along the plasma membrane and contained electron-dense deposits within their
cytoplasm. Surface epithelial cells sloughed from the gills and had features consistent with apoptosis, including
rounded shape, loss of surface microridges, and hypercondensation of nuclear chromatin. Affected areas of gills had
fusion of secondary lamellae with interlamellar spaces occupied by mitotic epithelial cells and eosinophils.
Eosinophils contained abundant fusiform-shaped granules that measured approximately 1 mm long and 360 nm
wide. The granule consisted of an electron-dense matrix with a central inclusion that was less electron-dense,
consisting of particulate and fibrillar material. In many instances, the central inclusion appeared empty and 90% of
the eosinophils had morphology suggestive of piecemeal degranulation. Also observed within affected areas were a
few neutrophils, mucous cells releasing mucus, and a small number of dendritic-like cells.

Amoebic gill disease is common problem for cultured Atlantic salmon within seawater net pens in Tasmania,
Australia
 AGD associated with colonization of amphizoic amoeba Neoparamoeba spp.
 Distinguishing feature of Neoparamoeba genus is presence of Perkinsiella amoebae-like organism, also referred
to as the parasome
 Affects Atlantic salmon and rainbow trout, as well as: turbot (Scophthalmus maximus), sea bream (Sparus
aurata), and sea bass (Dicentrarchus labrax)
 Clnical signs and problems with AGD: raised white mucoid patches on gill filaments, lethargy, and flared
opercula, and respiratory and acid-base disturbances and systemic hypertension
 Outbreaks associated with water temperatures between 12-20 C
o Other risk factors identified are: algae, site characteristics, and water chemistry
 Most prominent change in infected gills is degeneration of surface epithelium with hyperplasia of underlying
epithelial cells expressing proliferating cell nuclear antigen histologically, as well as down-regulation of tumorsuppressor protein p53 in affected gills
 Early attachment of amoebae caused hypertrophy and desquamation of epithelium, followed by hyperplasia
leading to fusion of the secondary lamellae
o Affected areas infiltrated with predominantly neutrophils
o Large numbers of eosinophilic granule cells reported surroundeing primary filament cartilage of
infected fish
o Inflammatory response may be more detrimental than curative
 Gross and histopathology
o Hyperplasia of epithelium with fusion of secondary lamellae with amoebae on secondary lamellae
o Heavy infiltrate of inflammatory cells
 Predominantly of cells resembling eosinophils
 Cells measured between 6 and 15mm along their axis
 Nuclei rounded in most cells, and occasionally indentation on one side
 Contained abundance of unique granules
o Fusiform
o Along long axis of granules is density composed of particulate and fibrillar
material, which is less electron-dense than rest of granules
o Granules were spheric and electron-lucent inclusion seen in center or offcenter
 Neutrophils also present, and goblet cells observed releasing contents in lesional areas
 Eosinophilic granular cells determined to be most likely eosinophils
 Piecemeal degranulation – selective release of granule proteins, characterized by increase in vesicles within
cytoplasm of cell and loss of material from granules without granule-granule or granule-plasma membrane fusion
 Also, a small number of dendritic-like cells with rod shaped granules containing square-latticed structured
material, which occasionally vacuolated on one end
o Contain granules similar to Birbeck granules found in mammalian Langerhans cells
Ultrastructural examination of the host cellular response in the gills of Atlantic Salmon, Salmo
salar, with amoebic gill disease
Exotic/fish
Immunology/infectious disease
Vet Path 44:663-671 (’07)
o
o
Granules are rod-shaped, containing square-lattice structured material and commonly vacuolated at one
end
Role in disease is unknown at this time
Board question – What is the primary cell type involved in immunity with amoebic gill disease
Ultrastructural examination of the host cellular response in the gills of Atlantic Salmon, Salmo
salar, with amoebic gill disease
Exotic/fish
Immunology/infectious disease
Vet Path 44:663-671 (’07)
Gill; Atlantic salmon. Amoeba (A) has
pseudopodia within the surface epithelial layer (E),
where the epithelial cells affected by the amoeba have a
distorted shape and loss of surface microridges. Uranyl
acetate and lead citrate. Bar = 3 m.
Gill; Atlantic salmon. Amoeba (A) are
located near the surface epithelium (E) of the gills. Bar = 2
m. Inset: An area of the amoeba near the
epithelium where the amoeba plasma membrane is
increasingly electron-dense (arrow) and electron-dense
deposits are seen within the amoeba (arrowheads). Uranyl
acetate and lead citrate. Bar = 700 nm.
Gill; Atlantic salmon. Eosinophil-containing
electron-dense fusiform granules (arrow) have
fibrillar inclusions that are less electron-dense.
Arrowheads indicate plasma membrane. N = nucleus.
Uranyl acetate and lead citrate. Bar = 1 m.
Gill; Atlantic salmon. The cytoplasm of
eosinophil-containing granules has electron-lucent crystalloid
inclusions (arrows) and an abundance of cytoplasmic vesicles
(arrowheads). Uranyl acetate and lead citrate. Bar = 500 nm.