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Diseases of Aquatic Organisms

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DAO 51:203-216 (2002)  -  doi:10.3354/dao051203

Comparison of in vitro-cultured and wild-type Perkinsus marinus. II. Dosing methods and host response

Marnita M. Chintala1,*, David Bushek2, Susan E. Ford3

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

ABSTRACT: Endoparasites must breach host barriers to establish infection and then must survive host internal defenses to cause disease. Such barriers may frustrate attempts to experimentally transmit parasites by Œnatural¹ methods. In addition, the host¹s condition may affect a study¹s outcome. The experiments reported here examined the effect of dosing method and host metabolic condition on measures of virulence for the oyster parasite Perkinsus marinus. Oysters, Crassostrea virginica, were challenged with wild-type and cultured forms of P. marinus via feeding, shell-cavity injection, gut intubation and adductor-muscle injection. For both parasite types, adductor-muscle injections produced the heaviest infections followed by shell-cavity injection, gut intubation, and feeding. There was no difference in parasite burdens between oysters fed cultured cells by acute vs chronic dosing, and parasite loads stabilized over time, suggesting a dynamic equilibrium between invasion and elimination. P. marinus distribution among tissues of challenged oysters indicated that parasites invaded the mantle and gill, as well as the gut, which has been considered the primary portal of entry. Frequency distributions of P. marinus in oysters challenged with 3 different culture phases indicated an aggregated distribution among hosts and suggested that stationary-phase parasites were easiest for the oyster to control or eliminate and log-phase parasites were the most difficult. Host metabolic condition also affected experimental outcomes, as indicated by increased infection levels in oysters undergoing spawning and/or exposed to low oxygen stress.

KEY WORDS: Disease · Parasite · Oyster · Crassostrea virginica · Portal of entry · Metabolic condition

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