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Diseases of Aquatic Organisms

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DAO 51:187-201 (2002)  -  doi:10.3354/dao051187

Comparison of in vitro-cultured and wild-type Perkinsus marinus. I. Pathogen virulence

Susan E. Ford1,*, Marnita M. Chintala2, David Bushek3

1Haskin Shellfish Research Laboratory, Institute of Marine and Coastal Sciences, Rutgers University, 6959 Miller Avenue, Port Norris, New Jersey 08349, USA
2United 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
3Baruch 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

ABSTRACT: Perkinsus marinus is a highly contagious pathogen of the eastern oyster Crassostrea virginica. Until recently, transmission studies have employed wild-type parasites isolated directly from infected oysters. Newly developed methods to propagate P. marinus in vitro have led to using cultured parasites for infection studies, but results suggest that cultured parasites are less virulent than wild-type parasites. In this paper, we report results of experiments designed to quantify differences between wild-type and cultured P. marinus virulence and to test the following hypotheses: (1) in vitro-cultured parasites are less virulent than wild-type parasites; (2) virulence decreases gradually during in vitro culture; (3) virulence of in vitro cultures can be restored by in vivo passage; (4) virulence changes with culture phase. Our results demonstrate that parasites freshly isolated from infected hosts are much more virulent than those propagated in culture, indicating a potential deficiency in the culture medium used. Virulence was lost immediately in culture and, for that reason, the practice of repassing cultured cells through the host to restore virulence does not work for P. marinus. Virulence was also associated with culture phase: log-phase parasites were significantly more virulent than those obtained from lag- or stationary-phase cultures.

KEY WORDS: Disease · Parasite · Oyster · Crassostrea virginica · Loss of virulence · Culture phase

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