DAO 51:217-225 (2002)  -  doi:10.3354/dao051217

Comparison of in vitro-cultured and wild-type Perkinsus marinus. III. Fecal elimination and its role in transmission

David Bushek1,*, Susan E. Ford2, Marnita M. Chintala3

1Baruch Marine Field Laboratory, Belle W. Baruch Institute for Marine Biology and Coastal Research, University of South Carolina, PO Box 1630, Georgetown, South Carolina 29442, USA
2Haskin Shellfish Research Laboratory, Institute of Marine and Coastal Sciences, Rutgers University, 6959 Miller Avenue, Port Norris, New Jersey 08349, USA
3United States Environmental Protection Agency (US EPA), Office of Research and Development (ORD), National Health and Environmental Effects Laboratory (NHEERL), Atlantic Ecology Division, 27 Tarzwell Drive, Narragansett, Rhode Island 02882, USA

ABSTRACT: Perkinsus marinus, a pathogen of the eastern oyster Crassostrea virginica, is transmitted directly among oysters. Previous studies found viable P. marinus parasites in the feces and pseudofeces of oysters within hours of injection with parasites, suggesting that the parasite may be voided from live oysters and subsequently dispersed in the water column. The experiments described here were designed to quantify P. marinus shed in the feces and pseudofeces of experimentally infected oysters. The results indicated that parasites were shed in 2 phases. A Œdecreasing¹ phase occurred within 2 wk of challenge and before net parasite proliferation began in the host. An Œincreasing¹ phase occurred after P. marinus had begun replicating. The quantity of P. marinus recovered in the feces and pseudofeces of exposed oysters was only about 5% of the dose administered. In vitro-cultured P. marinus were eliminated at a greater rate than wild-type P. marinus and the fraction discharged was not associated with culture phase. Oysters that were continuously dosed with P. marinus in their food gradually lost the ability to discard the parasite in pseudofeces. The quantity of P. marinus shed in feces of infected oysters was correlated with both the P. marinus body burden and subsequent survival time, suggesting that noninvasive fecal counts could predict infection intensity and survival. The results indicate that in an epizootic, shedding of P. marinus via feces is relatively small compared to the potential number released by cadavers of heavily infected oysters, but that fecal discharge may be important in transmission before infections become lethal.

KEY WORDS: Disease · Parasite · Oyster · Crassostrea virginica · Infection · Modes of transmission

Full text in pdf format