Cryptobiosis and Spironucleosis:
Cryptobiosis and Spironucleosis

Salmonid Cryptobiosis [Figs. 1 - 4]
Complete list of papers on
Cryptobia and cryptobiosis

Fig. 1: Cryptobia (T.) salmositica with a red cell from an anemic fish Fig. 2: Bilateral exophthalmia in acute salmonid cryptobiosis
Fig. 3: Splenomegaly (6 - 8 times by volume) Fig. 4: General edema and abdominal distension with ascites
Salmonid cryptobiosis is caused by the hemoflagellate, Cryptobia salmositica (Figs. 1; Woo, 2003). The parasite is transmitted by leeches (Piscicola salmositica) in streams and rivers on the Pacific coast of North America; however, direct transmission can also occur when infected and uninfected fish are held for prolonged periods in the same tank or under certain hatchery conditions.Clinical signs include anorexia, exophthalmia (Fig. 2), splenomegaly (Fig. 3), hepatomegaly, general edema and abdominal distention with ascites (Fig. 4), a microcytic and hypochromic anemia,and red cells are antiglobulin positive. Infected salmonids are susceptible to hypoxia, and their metabolism and swimming performance are reduced. Also, the lytic activities of complement in sera of infected fish are reduced, and the ability of infected fish to mount a protective response against a secondary pathogen and/or antigen is depressed. The anemia and anorexia in infected fish contribute to the immunodepression. The pathogen has at least two proteases - the cysteine protease is a metabolic enzyme while metalloprotease (a histolytic enzyme) is the main virulent factor.

The program on cryptobiosis is a multidisciplinary study. It is on the biology of the pathogen, diagnosis of infection, pathobiology in cryptobiosis including elucidation of the disease mechanism, host immune responses, and the development of 'proof-of-concept' strategies against the parasite and disease (Woo, 2003). Preventive strategies include exploiting innate and adaptive immunity, chemotherapy and immunochemotherapy (Woo, 2010).

Gene Sequences of Cryptobia salmositica in GENBANK
(1) Jesudhasan, P.R.R. & P.T.K. Woo (2004) Methionine adenosyltransferase gene. GENBANK No. AY603961.
(2) Jesudhasan, P.R.R. & P.T.K. Woo (2004) Major surface glycoprotein metalloproteinase gene - key gene involved in pathogensis. GENBANK No. AY632692.
(3) Jesudhasan, P.R.R. & P.T.K. Woo (2004) Cysteine proteinase gene. GENBANK No. AY713477.

Salmonid Spironucleosis [Figs. 4 - 8]
Systemic spironucleosis is caused by Spironucleus (
Fig. 4) - the parasite is in the blood and internal organs of salmonids. The parasite causes morbidity and mortality in fishes and there have been outbreaks of the disease in salmon cultured in sea cages - in chinook salmon on the west coast of Canada and in Atlantic salmon in Norway. Fish mortality was high and some infected chinook salmon had abdominal distensions and were anemic while infected Atlantic salmon were significantly smaller than healthy fish and they behaved'abnormally' prior to death. Little is known about the biology of the pathogen nor factors that precipitated the outbreaks, and there are at present no preventive nor control strategies against the parasite and the disease. (Woo, 2006. Chapter 3. In:
Fish Diseases and Disorders, Vol. 1: Protozoan and Metazoan Infections, 2nd edition, pages 46-114).


Spironucleus barkhanus has a blood and a tissue phase in experimentally infected Atlantic salmon. It first appears in the blood about a week after infection in some fish and the parasitaemia peaks at about 6 weeks. The parasite is not detectable in the blood at about 8 weeks after infection but it occurs in high numbers in the spleen, liver, eye socket, and muscles.Thirty eight out of 40 infected fish died in one experiment, and mortality was equally high (29 out of 30 infected fish) in another experiment with Atlantic salmon from 3 families of fish. Clinical signs of spironucleosis include unilateral exophthalmia (Fig. 6), skin blisters and ulcerations (Fig. 7), enlarged and globulated spleens (Fig. 8), livers with whitish to yellowish nodules,and haemorrhaging in organs. The parasite can be experimentally transmitted by inoculation of infected blood or through co-habition of infected and uninfected fish (Guo & Woo, 2004).

Fig. 5: Spironucleus in salmon Fig. 6: Unilateral exophthalmia Fig. 7: Ulceration on body surface Fig. 8: Globulated and enlarged spleen