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Abstracts
Workgroup: Frontiers in Disease Research
Life Cycle Studies Of Haplosporidium nelsoni (MSX): Spores And Non-Oyster Hosts
Principal Investigator(s):
Susan E. Ford, Rutgers University, Haskin Shellfish Research Laboratory, susan@hsrl.rutgers.edu
Funding Period: January 1, 1993 - March 31, 1995
Since its identification as the cause of devastating mortalities of eastern oysters, Crassostrea virginica, in the mid-Atlantic beginning in the late 1950s, the causative agent, Haplosporidium nelsoni, has been under intensive investigation. Early efforst at defining the life cycle were inconclusive, but suggested the possibility of another host. A group of outside experts attending an ODR-funded workshop on the "Life Cycle and Transmission of H. nelsoni " in 1992 urged that a renewed effort be made to search for potential non-oyster hosts and made some suggested as to how to go about this.
The primary objective of this project was to initiate a methodical, but restricted, search for potential alternate or intermediate hosts of H. nelsoni by collecting and screening at selected periods and locations a) zooplankters (intermediate host dissimilar to oysters, which could act as a dispersal mechanism for the parasite) and b) a number small bivalve species (alternate host similar to oyster spat in which H. nelsoni spores are produced). We also continued our sampling of oyster spat for H. nelsoni spores and our attempts to identify the ingested haplosporidan spores.
Over 1200 individual bivalves and other benthic organisms, and thousands of zooplankters, were collect and examined histologically during the study. Although the species representation was far from equal (e.g., 586 Tellina sp. vs 2 Lyonsia sp.), it did represent the relative frequency as well as the total abundance of these species at the collection site. Trematodes and cestodes were common in the bivalves and were also found in Diopatra sp. and Balanus sp. No recognizable protozoans were found in the bivalves and only one copepod and one polychaete were found to have microsporidian infections.
No H. nelsoni spores were found in any of the 1500 oyster spat or yearlings examined and, for the most part, total infection prevalence was very low, as it was in other oysters examined during the study period (0 - 30%). We continued to find ingested haplosporidan spores in both fresh and fixed material, but in much lower abundance than in earlier years.
Despite histological examination of several thousand individual potential non-oyster hosts, we did not find any parasites that we could link to H. nelsoni. The extraordinarily low prevalence of H. nelsoni in oysters in Delaware Bay during the study, even in susceptible groups, indicated that infection pressure (i.e., abundance of infective stages) was minimal. Consequently, interpretation of our negative results is very difficult. A number of scenarios are possible:
1) A non-oyster host was among the species examined, but the low H. nelsoni prevalence during the study (as measured in oysters) precluded finding the parasite in this host.
2) A non-oyster host was among the groups (i.e., small bivalves or zooplankters) examined, but was scarce or absent during the study.
3) A non-oyster host exists, but is not among the organisms that we examined.
4) The life cycle is direct, with oyster spat providing the infective stages (spores).
Because our study was not able to verify or eliminate any of the above possibilities, continued efforts must be made to evaluate potential intermediate or alternate hosts for H. nelsoni. Zooplankton and small bivalves remain strong candidates. Additionally, the potential role of oyster spat in the parasite's life cycle must be kept in mind.
PROJECT PUBLICATIONS:
Barber, R.D., S.A. Kanaley, and S.E. Ford. 1991. Evidence for regular sporulation by Haplosporidium nelsoni (=MSX) (Ascetospora: Haplosporidiidae) in spat of the American oyster, Crassostrea virginica . J. Protozool. 38(4):305-306.
Littlewood, D. T. J., S. E. Ford, and D. Fong. 1991. Small subunit rRNA gene sequence of Crassostrea virginica (Gmelin) and a comparison with similar sequences from other bivalve molluscs. Nucleic Acids Research 19(21):6048.
Barber, R. D. and S. E. Ford. 1992. Occurrence and significance of haplosporidan spores in the digestive tract of the eastern oyster, Crassostrea virginica. J. Shellfish Res. 11(2):371-376.
Ford, S. E., K. A. Alcox, and S. A. Kanaley. 1993. In vitro interactions between bivalve hemocytes and the oyster pathogen Haplosporidium nelsoni. J. Parasitol. 79 (2):255-265.
Fong, D., M. M. Chan, R. Rodrigues, C. C. Chen, Y. Liang, D. T. J. Littlewood, and S. E. Ford. 1993. Small subunit ribosomal RNA gene sequence of the parasitic protozoan Haplosporidium nelsoni provides a molecular probe for the oyster MSX disease. Mol. Biochem. Parasitol. 62:139-142.
Fong, D., R. Rodriguez, K. Koo, J. Sun, M. L. Sogin, D. Bushek, T. D. J. Littlewood, and S. E. Ford. 1993. Small subunit ribosomal RNA gene sequence of the oyster parasite Perkinsus marinus. Mol. Mar. Biol. Biotech. 2(6):346-350.
Ford, S. E., K. A. Ashton-Alcox, and S. A. Kanaley. 1994. Comparative cytometric and microscopic analyses of oyster hemocytes J. Invertebr. Pathol. 64:114-122
Ko, Y.-T., S. E. Ford, and D. Fong. 1995. Characterization of the small subunit ribosomal RNA gene of the oyster parasite Haplosporidium costale. Mol. Mar. Biol. Biotech. 4(3):236-242.
Bushek, D., S. K. Allen Jr, K. A. Alcox, R. Gustafson, and S. E. Ford. 1997. Response of Crassostrea virginica to in vitro cultured Perkinsus marinus: preliminary comparisons of three inoculation methods J. Shellfish Res. 16: 479-485.
Ford, S. E., R. D. Barber, and E. Marks. 1997. Disseminated neoplasia in juvenile eastern oysters, Crassostrea virginica, and its relationship to the reproductive cycle. Dis. Aquat. Org. 28:73-77.
Ashton-Alcox, K.A. and S.E. Ford. 1998. Variability in molluscan hemocytes: a flow cytometric study. Tissue & Cell, 30 (2) 195-204.
Ford, S.E. and K. A. Ashton-Alcox. 1998. Altered response of oyster hemocytes to Haplosporidium nelsoni (MSX) plasmodia treated with enzymes or metabolic inhibitors. J. Invertebr. Pathol. 72(2):160-166.
Ford, S.E., A. Schotthoefer, and C. Spruck. 1999. in vivo dynamics of the microparasite Perkinsus marinus during progression and regression of infections in eastern oysters. J. Parasitol. 85(2):273-282.
Ko, Y-T., M. M-Y. Chan, S. E. Ford, and D. Fong. 1999. A PCR-ELISA method for direct detection of the oyster pathogen Haplosporidium nelsoni. Marine Biotechnol. 1:147-154.
Ford, S. E., E. N. Powell, J. M. Klinck, and E. E. Hofmann. 1999. Modeling the MSX parasite in the eastern oyster (Crassostrea virginica). I. Model development, implementation and verification. J. Shellfish Res. 18 (2):475-500.
Paraso, M. C., S. E. Ford, E. N. Powell, E. E. Hofmann, and J. M. Klinck,. 1999. Modeling the MSX parasite in the eastern oyster (Crassostrea virginica). II. Salinity effects J. Shellfish Res. 18 (2):501-516.
Powell, E. N., S. E. Ford, J. M. Klinck, and E. E. Hofmann and S. Jordan. 1999. Modeling the MSX parasite in the eastern oyster (Crassostrea virginica). III. Delaware and Chesapeake Bay comparisons and the question of transmission. J. Shellfish Res. 18 (2):517-537.
Ford, S.E., Xu, Z. and DeBrosse, G. 2001. Use of particle filtration and UV irradiation to prevent infection by Haplosporidium nelsoni (MSX) and Perkinsus marinus (Dermo) in hatchery-reared larval and juvenile oysters. Aquaculture 194:37-49.
Hofmann, E., S. Ford, E. Powell, J. Klinck. (2001). Modeling studies of the effect of climate variability on MSX disease in eastern oyster (Crassostrea virginica) populations. Hydrobiologia 460:195-212
Ford, S. E., M.M. Chintala and D. Bushek. 2002. Comparison of in vitro cultured and natural Perkinsus marinus I. Pathogen virulence. Dis. Aquat. Org. 51:187-201.
Chintala, M.M., D. Bushek and S. E. Ford. Comparison of in vitro cultured and natural Perkinsus marinus I.I Dosing methods and host response. Dis. Aquat. Org. 51:203-216.
Bushek, D., S. E. Ford and M.M. Chintala. 2002. Comparison of in vitro cultured and natural Perkinsus marinus III. Fecal elimination and its role in transmission. Dis. Aquat. Org. 51:217-225.
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