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==Introduction==

==Introduction==

Cryptobia species are '''bi-flagellated [[Protozoa|protozoan]] pathogens''' that infect a range of vertebrate and invertebrate hosts but are known for causing disease as both '''endoparasites and ectoparasites of fish'''. ''C. branchialis'' is the only '''ectoparasite''' of the five pathogenic species listed above. They may be found on the '''body surface or gills''' of host fish while endoparasitic species may reside within the '''intestine or the blood'''. Blood parasites have ectoparasitic life stages on the external body surface.

Cryptobia species are '''bi-flagellated [[Protozoa|protozoan]]''' that infect a range of vertebrate and invertebrate hosts. A few species are known for causing disease as both '''endoparasites and ectoparasites of fish'''. ''C. branchialis'' is the only '''ectoparasite''' of the five pathogenic species listed above. They may be found on the '''body surface or gills''' of host fish while endoparasitic species may reside within the '''intestine or the blood'''. A couple of blood parasites have ectoparasitic life stages on the external body surface.

The parasites are '''oval or ribbon-like''' in shape with both flagellae attached to their anterior end. One flagellum is '''recurrent''' and ends freely at the posterior end of the cell. They also have a very prominent kinetoplast. Replication is by binary fission.<ref>Woo, P. T. K (1987) '''Cryptobia and cryptobiosis in fishes'''. ''Advances in Parasitology'', 26:199-237</ref>

The parasites are '''oval or ribbon-like''' in shape with both flagellae attached to their anterior end. One flagellum is '''recurrent''' and ends freely at the posterior end of the cell. They also have a very prominent kinetoplast. Replication is by binary fission.<ref>Woo, P. T. K (1987) '''Cryptobia and cryptobiosis in fishes'''. ''Advances in Parasitology'', 26:199-237</ref>

''C. bullocki'' is isolated in marine fish in the '''USA and Northern Gulf of Mexico'''.

''C. bullocki'' is isolated in marine fish in the '''USA and Northern Gulf of Mexico'''.

''C. iubilans'' is associated with the '''intestine''' and therefore transmitted '''faecally''', while ''C. salmositica, C. bullocki'' and ''C. borreli'' are '''haematozoic species''' and therefore '''transmitted by bloodfeeding leeches'''. Some are also excreted in '''mucus'''. ''C. salmositica'' has been diagnosed where no leeches were found so is more poorly understood<ref> Becker, C. D., Katz, M (1965) '''Distribution, ecology, and biology of the salmonid leech, Piscicola salmositica (Rhynchobdellae: Piscicolidae)'''. ''J Fisheries Research Board of Canada'', 22:1175-1195</ref>. Parasites enter the recipient fish via '''surface lesions or the gills'''. Transmission via the water in shared tanks is efficient and is only slightly reduced when fish are separated by wire screens.

''C. iubilans'' is associated with the '''intestine''' and therefore transmitted '''faecally''', while ''C. salmositica, C. bullocki'' and ''C. borreli'' are '''haematozoic species''' and therefore '''transmitted by bloodfeeding leeches'''. Some are also found in surface '''mucus'''. ''C. salmositica'' has been diagnosed where no leeches were found so transmission is poorly understood<ref> Becker, C. D., Katz, M (1965) '''Distribution, ecology, and biology of the salmonid leech, Piscicola salmositica (Rhynchobdellae: Piscicolidae)'''. ''J Fisheries Research Board of Canada'', 22:1175-1195</ref>. It has been suggested that parasites enter the recipient fish via '''surface lesions or the gills'''. Transmission via the water in shared tanks is efficient and is only slightly reduced when infected and non-infected fish are separated by wire screens.

==Signalment==

==Signalment==

Many species of both '''marine and freshwater''' fish are infected. Although salmonids are often of prime concern, resident fish, such as flatfish in Chesapeake Bay are also affected. Interestingly, these native fish survive the disease if kept in water maintained at 10-13⁰C after infection but die if water is 5⁰ or below.

Many species of both '''marine and freshwater''' fish are infected. Although salmonids are often of prime concern, resident fish, such as flatfish in Chesapeake Bay are also affected. Interestingly, these native fish survive the disease if kept in water maintained at 10-13⁰C after infection but die if water is 5⁰ or below.

''C. bullocki'' causes disease and mortality in '''marine''' fish. ''C. salmositica'' has also been found on fish in sea water. The rest of the pathogenic species are '''usually parasitic to freshwater species'''.

''C. bullocki'' causes disease and mortality in '''marine''' fish. ''C. salmositica'' has also been found on fish in sea water. The remaining pathogenic species are '''parasitic to freshwater fish'''.

Leech numbers increase in '''November''' and so prevalence and severity of parasitaemia are higher in haematozoic infections during the northern hemisphere Winter.<ref>Bower, S. M., Margolis, L (1984) '''Detection of infection and susceptibility of different Pacific salmon stocks (Oncorhynchus spp.) to the haemoflagellate Cryptobia salmositica'''. ''J Parasitology'', 70(2):273-278</ref>

Leech numbers increase in '''November''' and so prevalence and severity of parasitaemia are higher in haematozoic infections during late Autumn and Winter in the northern hemisphere.<ref>Bower, S. M., Margolis, L (1984) '''Detection of infection and susceptibility of different Pacific salmon stocks (Oncorhynchus spp.) to the haemoflagellate Cryptobia salmositica'''. ''J Parasitology'', 70(2):273-278</ref>

==Clinical Signs and Pathology==

==Clinical Signs and Pathology==

=== ''C. salmositica'' – Haematozoic Endoparasite ===

=== ''C. salmositica'' – Haematozoic Endoparasite ===

'''Exophthalmia, splenomegaly, hepatomegaly, oedema, ascites, [[Anaemia|anaemia]] and marked emaciation''' are signs of infection with the blood-borne ''C. salmositica''. Anaemia is usually '''microcytic and hypochromic''', caused by '''haemolytic action of parasitic secretions (haemolysin)''' and '''antigen release''' after immune destruction (immune complex driven). Obvious lesions are present in '''haematopoietic tissues''' of infected fish. '''Immunosuppression''' is also marked. Anorexia can be an important contributor to immunosuppression.

'''Exophthalmia, splenomegaly, hepatomegaly, oedema, ascites, [[Anaemia|anaemia]] and marked emaciation''' are signs of infection with the blood-borne ''C. salmositica''. Anaemia is usually '''microcytic and hypochromic''', caused by '''haemolytic action of parasitic secretions (haemolysin, subsequently identified as a metalloprotease)''' and '''antigen release''' after immune destruction (immune complex driven). Obvious lesions are present in '''haematopoietic tissues''' of infected fish. '''Immunosuppression''' is also marked. Anorexia can be an important contributor to immunosuppression.

Infected fish are also '''more sensitive to environmental hypoxia''' due to occlusion of blood vessels by parasites and consequently impaired perfusion. This can be an important exacerbating factor of mortality when oxygen supply is already restricted due to overcrowding, slow flow or algal blooms.<ref>Woo, P. T. K., Wehnert, S. D (1986) '''Cryptobia salmositica: susceptibility of infected rainbow trout, Salmo gairdneri, to environmental hypoxia'''. ''Journal of Parasitology'', 72(3):392-396</ref>

Infected fish are also '''more sensitive to environmental hypoxia''' due to the anaemia and occlusion of blood vessels by parasites and consequently impaired perfusion. This can be an important exacerbating factor of mortality when oxygen supply is already restricted due to overcrowding, slow flow or algal blooms.<ref>Woo, P. T. K., Wehnert, S. D (1986) '''Cryptobia salmositica: susceptibility of infected rainbow trout, Salmo gairdneri, to environmental hypoxia'''. ''Journal of Parasitology'', 72(3):392-396</ref>

Histopathological features include '''focal haemorrhages, vascular congestion and occlusion and oedematous changes''' in the renal glomeruli. Lesions can be present in the liver, gills and spleen also, and generalised inflammation progresses to mononuclear infiltration after 3 weeks. After this point, '''parasites are found extravascularly where they cause tissue necrosis.'''

Histopathological features include '''focal haemorrhages, vascular congestion and occlusion and oedematous changes''' in the renal glomeruli. Lesions can be present in the liver, gills and spleen also, and generalised inflammation progresses to mononuclear infiltration after 3 weeks. After this point, '''parasites are found extravascularly where they cause tissue necrosis.'''

'''Isometamidium chloride''' is effective against ''C. salmositica'' in Chinook salmon and can also be used prophylactically. It has also been used against other species.

'''Isometamidium chloride''' is effective against ''C. salmositica'' in Chinook salmon and can also be used prophylactically. It has also been used against other species.

A '''live vaccine''' is available which provides protection against ''C. bullocki'' and ''C. salmositica'' for 2 years.  

A '''live vaccine''' is available which provides protection against ''C. salmositica'' for 2 years.  

'''Selective breeding''' from resistant or asymptomatic breeds is also sensible.

'''Selective breeding''' from resistant or asymptomatic breeds is also sensible.

==References==

==References==

<references/>

<references/>

Woo, P. T. K (2001) '''Cryptobiosis and its control in North American fishes'''. International Journal for Parasitology, 31(5/6):566-574.

Woo, P. T. K (2001) '''Cryptobiosis and its control in North American fishes'''. ''International Journal for Parasitology'', 31(5/6):566-574.

 

Woo, P.T.K. (2006) '''Diplomonadida (Phylum Parabasalia) and Kinetoplastea (Phylum Euglenozoa)'''. In: '''Fish Diseases and Disorders Volume 1''': Protozoan and Metazoan Infections (ed. P.T.K. Woo), ''CABI'', Walingford, UK, pp. 46-115.

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[[Category:Fish Diseases]]

[[Category:Fish Diseases]]

[[Category:CABI Expert Review]]

[[Category:CABI Expert Review]]