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Abstracts
Workgroup: Frontiers in Disease Research
Relationships between disseminated Perkinsus marinus cell abundance, water temperature, salinity, host oyster mortality rate, and dermo disease transmission rate, in Chesapeake Bay waters
Principal Investigator(s):
Christopher F. Dungan, Maryland Dept. of Natural Resources, Oxford Laboratory, Oxford, MD, cdungan@dnr.state.md.us
Co-Investigator(s):
Dr. Bob S. Roberson, University of Maryland, College Park, MD
Dr. Eugene M. Burreson, Virginia Institute of Marine Science, Gloucester Point, VA
Dr. Eugene M. Burreson, Virginia Institute of Marine Science, Gloucester Point, VA
Funding Period: 4/1/95 - 12/31/95
Employed new flow cytometric immunoassays of high-frequency water samples collected in dermo disease-endemic Chesapeake Bay waters at Oxford, MD and Gloucester Point, VA to estimate seasonal disseminated Perkinsus marinus cell abundances in environmental waters, and inter-annual variability in timing and magnitudes of dermo disease infection pressure peaks.
Found that conservatively estimated peak disseminated parasite cell abundances varied from 3,000 - 12,000 cells/liter between sampling sites, and between years at each sampling site.
Found that peak parasite abundance timing varied annually during July and August at the VIMS site, and between June and August at the Oxford site.
Found that peak host oyster mortality rates both closely preceded and closely followed peak parasite abundances at the VIMS site, but consistently followed peak parasite abundances at the Oxford site, suggesting that significant parasite dissemination regularly precedes peak mortality of infected hosts, and may also follow mortality peaks.
Found that maximum new infection acquisition rates by uninfected sentinel oysters deployed and retrieved biweekly at the VIMS site coincided temporally with periods of high measured parasite abundances, but that infection incidences and parasite abundances were not statistically correlated due to infrequent infection of sentinel oysters during periods of low parasite abundance. Highest dermo disease transmission rates occurred during periods of high disseminated parasite abundances, and low transmission rates persisted during periods of low parasite abundances.
Found that earliest lesions in newly infected laboratory and environmentally exposed oysters, occurred most frequently in external epithelia and connective tissues of the gills and mantle, and less frequently in gut epithelia. The importance former
IMPACTS and/or BENEFITS:
Results validated a new technical method that was developed for estimating real-time dermo disease infection pressure, by analysis of environmental water samples.
The proposed mechanism for dermo disease transmission as following death and decomposition of infected oysters was supported, and was expanded by evidence suggesting that significant parasite dissemination also precedes host mortality.
Oyster resource management strategies for avoidance of dermo disease transmission were informed by direct measurements of the seasonality and relative intensities of infection pressures in high- and moderate-salinity environments, and of interannual variations in both timing and intensity of infection pressures at individual sites.
Known avenues through which P. marinus infects oyster hosts were expanded to include non-gut portals that do not require pathogen ingestion, as significant invasion sites.
PROJECT PUBLICATIONS:
Ragone Calvo L.M., Dungan C.F., Roberson B.S., and Burreson, E.M. submitted A systematic evaluation of factors controlling Perkinsus marinus transmission dynamics in the lower Chesapeake Bay. Dis. Aquat. Org.
Ragone Calvo L.M., Burreson, E.M., Dungan C.F., and Roberson B.S. 1996. Perkinsus marinus transmission dynamics in Chesapeake Bay. J. Shellfish Res. 15:496 (abstract)
Dungan C.F., Hamilton R.M., Ragone Calvo L.M., and Burreson E.M. 1996. Identification of Perkinsus marinus portals of entry by histochemical immunoassays of challenged oysters. J. Shellfish Res. 15:500 (abstract)
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