temperatures are >15
C, while clinical disease and peak
mortality typically occurs between September and February.
The diagnosis is based upon demonstration of spores in
histological sections and supported by PCR.
8.5
Sarcomastigophora
8.5.1 Cryptobia salmositica
Cryptobia salmositica is a haemoflagellate that causes disease
in freshwater fish. The infected fish are typical cold-water
species occurring in streams with gravel beds and moderate
to swift flowing currents. Among salmonids, it has been
described from the gills, body surface and digestive system of
coho and pink salmon in fresh water. Brook trout can also
become infected but they do not appear to develop cryptobiasis,
and therefore, may act as a reservoir host. C. salmositica is
normally transmitted by the leech, Piscicola salmositica,
although direct transmission has also been demonstrated.
The first clinical sign is anaemia, followed by exophthalmia,
oedema, splenomegaly, hepatomegaly and abdominal distension resulting from ascites. Microcytic and hypochromic
anaemia is correlated with increasing parasitaemia and extravascular localization of the parasite. Histologically, the initial
lesions occur in the liver, gills and spleen, and comprise focal
haemorrhage with congestion of blood vessels and oedema in
the glomeruli. In addition, there is dilatation and oedematous
swelling of the glomeruli followed by endovasculitis and
mononuclear infiltration. Necrosis in the liver and kidney
with depletion of haematopoietic tissue in the acute phase
causes the mortality. A mucosal and submucosal granulomatous gastritis has also been reported.
C. salmositica measures 6–25 Â 2–4 μm, and possesses a
prominent kinetoplast either anterior to, or beside the round
nucleus, with both an anterior and posterior flagella.
Diagnosis can be achieved using stained blood films where
(Fig. 8.23). Additionally, a monoclonal antibody against
the 47- kDa antigen has been used in an antigen-capture
enzyme-linked immunosorbant assay.
8.5.2 Ichthyobodo spp.
Ichthyobodo necator (‘Costia’) is an important, obligate
parasite, capable of infecting a broad range of wild and
farmed fresh water fish. The parasite is associated with
skin epithelium, gills and in cavities, within hyperplastic
interlamellar tissue. Affected fish become emaciated, lethargic with flared opercula and they rub against the walls or
bottom of the tank. The fish may appear greyish due to
excessive skin mucous, and show focal skin haemorrhage.
Infestation are often associated with poor husbandry and
mortality may be high if the fish are left untreated.
A free-living and an attached form can be observed, the
first measures 10–15 μm in length and is usually oval or
kidney shaped, while the attached stage is cuneiform or pearlike. I. necator has two pairs of flagella and swims in a jerky
spiral manner.
Histologically, there is a reduction of mucous cells early
in the infection, while lamellar hyperplasia occurs in the
recovery phase (Figs. 8.24 and 8.25). Other lesions include
erosive and ulcerative dermatitis. Gill lesions include
exhaustion of the goblet cells, diffuse hyperplasia, sometimes with characteristic cavitation, and degeneration of
epithelial and mucous cells, fusion of adjacent lamellae
Fig. 8.23 Cryptobia salmositica in blood smear from Chinook
salmon. Erythrocytes are red, parasites are blue. Diff Quick stain.
Bar ¼ 20 μm
Fig. 8.22 Candidatus Paranucleospora theridon (¼Desmozoon
lepeophtheiri) in gill epithelium from Atlantic salmon. Gram stain.
Bar ¼ 20 μm
8.5 Sarcomastigophora
117
C, while clinical disease and peak
mortality typically occurs between September and February.
The diagnosis is based upon demonstration of spores in
histological sections and supported by PCR.
8.5
Sarcomastigophora
8.5.1 Cryptobia salmositica
Cryptobia salmositica is a haemoflagellate that causes disease
in freshwater fish. The infected fish are typical cold-water
species occurring in streams with gravel beds and moderate
to swift flowing currents. Among salmonids, it has been
described from the gills, body surface and digestive system of
coho and pink salmon in fresh water. Brook trout can also
become infected but they do not appear to develop cryptobiasis,
and therefore, may act as a reservoir host. C. salmositica is
normally transmitted by the leech, Piscicola salmositica,
although direct transmission has also been demonstrated.
The first clinical sign is anaemia, followed by exophthalmia,
oedema, splenomegaly, hepatomegaly and abdominal distension resulting from ascites. Microcytic and hypochromic
anaemia is correlated with increasing parasitaemia and extravascular localization of the parasite. Histologically, the initial
lesions occur in the liver, gills and spleen, and comprise focal
haemorrhage with congestion of blood vessels and oedema in
the glomeruli. In addition, there is dilatation and oedematous
swelling of the glomeruli followed by endovasculitis and
mononuclear infiltration. Necrosis in the liver and kidney
with depletion of haematopoietic tissue in the acute phase
causes the mortality. A mucosal and submucosal granulomatous gastritis has also been reported.
C. salmositica measures 6–25 Â 2–4 μm, and possesses a
prominent kinetoplast either anterior to, or beside the round
nucleus, with both an anterior and posterior flagella.
Diagnosis can be achieved using stained blood films where
(Fig. 8.23). Additionally, a monoclonal antibody against
the 47- kDa antigen has been used in an antigen-capture
enzyme-linked immunosorbant assay.
8.5.2 Ichthyobodo spp.
Ichthyobodo necator (‘Costia’) is an important, obligate
parasite, capable of infecting a broad range of wild and
farmed fresh water fish. The parasite is associated with
skin epithelium, gills and in cavities, within hyperplastic
interlamellar tissue. Affected fish become emaciated, lethargic with flared opercula and they rub against the walls or
bottom of the tank. The fish may appear greyish due to
excessive skin mucous, and show focal skin haemorrhage.
Infestation are often associated with poor husbandry and
mortality may be high if the fish are left untreated.
A free-living and an attached form can be observed, the
first measures 10–15 μm in length and is usually oval or
kidney shaped, while the attached stage is cuneiform or pearlike. I. necator has two pairs of flagella and swims in a jerky
spiral manner.
Histologically, there is a reduction of mucous cells early
in the infection, while lamellar hyperplasia occurs in the
recovery phase (Figs. 8.24 and 8.25). Other lesions include
erosive and ulcerative dermatitis. Gill lesions include
exhaustion of the goblet cells, diffuse hyperplasia, sometimes with characteristic cavitation, and degeneration of
epithelial and mucous cells, fusion of adjacent lamellae
Fig. 8.23 Cryptobia salmositica in blood smear from Chinook
salmon. Erythrocytes are red, parasites are blue. Diff Quick stain.
Bar ¼ 20 μm
Fig. 8.22 Candidatus Paranucleospora theridon (¼Desmozoon
lepeophtheiri) in gill epithelium from Atlantic salmon. Gram stain.
Bar ¼ 20 μm
8.5 Sarcomastigophora
117