Patrick T.K. Woo
Axelrod Institute of Ichthyology and Department of Zoology, University of Guelph, Ontario, Canada. E-mail: [email protected]
References.
Cryptobia salmositica is an elongated haemoflagellate with a prominent kinetoplast either anterior to, or beside, its round nucleus. It has two flagella which originate from the anterior end; one is free while the recurrent flagellum is attached to the body and ends as a posterior free flagellum. The parasite has been found in all species of Pacific salmon (Oncorhynchus spp.) in freshwater streams and rivers along the west coast of North America. It is normally transmitted by a blood sucking freshwater leech, Piscicola salmositica (see Woo, 1987; 1994); however, it can also be transmitted directly (in the absence of leeches) between fish under certain laboratory (Woo and Wehnert, 1983) and hatchery conditions (Bower and Margolis, 1983).
The parasite multiplies rapidly in the blood and causes disease and mortality in experimentally and naturally infected salmon. It is recognized as a lethal pathogen in semi-natural and intensive salmon culture facilities, and there is no chemotherapy against the disease (Woo and Poynton, 1995). The clinical signs of acute cryptobiosis include exophthalmia, splenomegaly, general edema, abdominal distension with ascites, a microcytic and hypochromic anemia (Woo, 1979), anorexia (Li and Woo, 1991), and their red cells give a positive antiglobulin reaction (Thomas and Woo, 1988). The immune system is depressed during acute cryptobiosis (Jones et al., 1986), and anorexia contributes to the immunodepression (Thomas and Woo, 1992). Infected fish are highly susceptible to environmental hypoxia (Woo and Wehnert, 1986), and their metabolism and swimming performance are also significantly reduced during acute cryptobiosis (Kumaraguru et al., 1995).
Some hatchery raised brook charr, Salvelinus fontinalis are susceptible to C. salmositica infection while others cannot be infected with the parasite (Ardelli et al., 1994). We can now selectively breed Cryptobia-resistant charr because this innate resistance to infection is controlled by a dominant gene. The gene is inherited in a simple Mendelian pattern by progenies of innately resistant fish (Forward et al., 1995). The parasite is lysed via the alternative pathway of complement activation in the blood of Cryptobia-resistant charr (Forward and Woo, 1996).
Rainbow trout Oncorhynchus mykiss, that survive the disease are resistant to disease (Jones and Woo, 1987), but this is at considerable bioenergetic cost to the fish (Beamish et al., 1996). We have attenuated C. salmositica and have used it sucessfully as a live vaccine; the avirulent strain does not cause disease but confers protection to vaccinated fish (Woo and Li, 1990). Vaccination does not affect growth of juvenile trout and it has no detectable bioenergetic cost to the fish (Beamish et al., 1996). The attenuated strain has remained avirulent for eight years; it has lost a few polypeptides (Woo and Thomas, 1991), and this includes its metallo-protease (Zuo and Woo, 1997). A single dose of the live vaccine protects both juvenile (Sitja-Bobadilla and Woo, 1994) and adult trout (Woo and Li, 1990; Li and Woo, 1995) from disease, and the protection lasts for at least 24 months. The efficacy of the vaccine is not affected when vaccinated trout are transferred from fresh water to sea water (Li and Woo, 1997). In vaccinated fish the production of complement-fixing antibodies increases rapidly after parasite challenge. Under in vitro conditions, activated macrophages from kidneys of vaccinated fish are very efficient in engulfing living parasites. The protective mechanism also involves antibody independent, and antibody dependent cell-mediated cytotoxicity (Li and Woo, 1995).
We have also produced an IgG 1 monoclonal antibody (MAb-001) against an exposed surface membrane glycoprotein (about 200 kDa) on C. salmositica. Mab-001 agglutinates the parasite but it does not fix complement to lyse the parasite under in vitro conditions. C. salmositica exposed to MAb-001 do not multiply and die within three weeks in tissue culture; this indicates that the antibody may interfere with the metabolism of the parasite. Also, Mab-001 coated parasites are not infective when injected into fish (Feng and Woo, 1996). When MAb-001 is injected into fish with acute cryptobiosis the antibody is therapeutic; it significantly lowers their parasitaemias by 60-80% in 48 hours (Feng and Woo, 1997).
Ardelli, B, F., Forward, G., M., and Woo P.T.K., 1994. Brook charr Salvelinus fontinalis) and cryptobiosis: A potential salmonid reservoir host for Crytobia salmositica Katz, 1951. J. Fish Dis, 17: 567-577.
Beamish, F.W.H., Sitja-Bobadilla, A., Jebbink, J.A, and Woo, P.T.K. 1996. Bioennergetic cost of cryptobiosis in fish: rainbow trout (Oncorynchus mykiss) infected with Cryptobia salmositica and with an attenuated live vaccine. Dis. Aquat. Org., 25: 1-8.
Bower, S. and Margolis, L., 1983. Direct transmission of the haemoflagellate Cryptobia salmositica among Pacific salmon (Oncorhynchus spp.). Can. J. Zool., 61: 1242-1250.
Feng, S. and Woo, P.T.K., 1996. Biological characterization of a monoclonal antibody againt a surface menbrane antigen on Cryptobia salmositica Katz, 1951. J. Fish Dis., 19: 137-143.
Feng, S. and Woo, P.T.K., 1997. The therapeutic and prophylactic effects of a protective monoclonal antibody Mab-001 against the pathogenic haemoflagellate Cryptobia salmositica Katz, 1951. Dis. Aquat. Org., 28: 211-219.
Forward, G. M., Ferguson, M.M. and Woo, P.T.K., 1995. Susceptibily of brook charr, Salvelinus fontinalis to the pathogenic haemoflagellate, Cryptobia salmosistica, and the inheritance of innate resistance by progenies of resistant fish. Parasitology, 111: 337-345.
Forward, G.M., and Woo, P.T.K., 1996. An in vitro study on the mechanism of innate immunity in Cryptobia-resistant brook charr Salvelinus fontinalis against Criptobia salmositica. Parasitol. Res., 82: 238-241.
Jones, S.R.M. and Woo, P.T.K., 1987. The immune repouse of rainbow trout Salmo gairdneri Richardson to the haemoflagellate Cryptobia salmositica Katz 1951. J. Fish. Dis., 10: 395- 402.
Jones, S.R.M., Woo, P.T.K., and Stevenson, R.M.W., 1986. Immunosuppression in Salmo gairdneri caused by the haemoflagellate, Cryptobia salmositica. J. Fish Dis., 9: 431.438.
Kumaraguru, A.K., Beamish, F.W.H., and Woo, P.T.K., 1995. Impact of a pathogenic haemoflagellate, Cryptobia salmositica on the metabolism and swimming performance of rainbow trout, Oncorhynchus mykiss (Walbaum). J. Fish Dis., 18: 297-305.
Li, S. and Woo, P.T.K., 1997. Vaccination of raibow trout, Oncorhynchus mykiss (Walbaum) against cryptobiosis: efficacy of the vaccine in fresh and sea water. J. Fish Dis., (in press).
Li, S. and Woo, P.T.K. 1995. Efficacy of a live Cryptobia salmositica vaccine, and the mechanism of protection in vaccinated Oncorhynchus mykiss (Walbaum) against cryptobiosis. Vet. Immunol. & Immunopathol., 48: 343 -353.
Li, S. and Woo, P.T.K., 1991. Anorexia reduces the severity of cryotobiosis in Oncorhynchus mykiss. J. Parasit, 77: 467-471.
Sitja - Bobadilla, A., and Woo, P.T.K. 1994. An enzyme-linked immunosorbent assay (ELISA) for the detection of antibodies against the pathogenic haemoflagellate, Cryptobia salmositica Katz and protection against cryptobiosis in juvenile Oncorhynchus mykiss (Walbaum) inoculated with a live Cryptobia vaccine. J. Fish Dis., 17: 399-408.
Thomas, P.T. and Woo, P.T.K., 1988. Cryptobia salmositica: in vitro and in vivo study on the mechanism of anaemia in infected rainbow trout, Salmo gairdneri. J. Fish Dis., 11: 425 - 431.
Thomas, P.T., and Woo, P.T.K. 1992. Anorexia in Oncorhynchus mykiss infeted with Crytobia salmositica (Sarcomastigophora: Kinetoplastida): Its onset and contribution to the immunodepression. J. Fish Dis., 15: 443-447.
Woo, P.T.K. and Li, S., 1990. In vitro attenuation of Cryptobia salmositica and its use as a live vaccine against criptobiosis in Oncorhynchus mykiss. J. Parasitol., 76: 752-755.
Woo, P.T.K. and Wehnert, S. D., 1986. Cryptobia salmositica: susceptibility of infected trout, Salmo gairdneri, to environmental hypoxia. J. Parasitol. 72: 392 - 396.
Woo, P.T.K. and Poynton, S., 1995. Diplomonadida, Kinetoplastida and Amoebida. In: P.T.K. Woo (Editor) Fish Diseases and Disorders I. Protozoan and Metazoan Infections. CAB International, Oxon, U.K. pp. 27-96.
Woo, P.T.K., 1987. Cryptobia and cryptobiosis in fishes. In J.R. Baker and R. Muller (Editors) Advances in Parasitology, Vol. 26. Academic Press, London, U.K. pp. 199-237.
Woo, P.T.K., 1994. Flagellate Parasites of Fish. In J.P. Kreier (Editor) Parasitic Protozoa, 2nd edition, Vol. VIII. Academic Press, New York. U.S.A. pp. 1-8.
Woo, P.T.K., 1979. Trypanoplasma salmositica: Experimental infections in rainbow troout, Saimo gairdneri. Exptl. Parasitol., 47: 36 - 48.
Woo, P.T.K., and Thomas, P.T. 1991. Polyptide and antigen profiles of Cryptobia salmositica, C. bullocki, and C. catostomi (Kineplastida: Sarcomastigophors) isolated from fishes. Dis. Aquat. Org., 11:201.205.
Woo, P.T.K., and Wehnert, S. 1983. Direct transmission of a haemoflagellate, Cryptobia salmositica Katz, 1951 (Kinetoplastida: Bodonina) between rainbow trout under laboratory conditions. J. Protozool., 39: 334-337.
Zuo, X., and Woo, P.T.K., 1997. Proteasis in pathogenic and nonpathogenic haemoflagellates, Cryptobia spp. (Sarcomastigophora: Kinetoplastida) fishes. Dis. Aquat. Org., (in press).
