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MARI/CCPO Seminar Series

Rise of a Marine Superbug: Understanding the Origins of Perkinsus marinus as the East Coast's Most Significant Oyster Pathogen

Ryan Carnegie, Virginia Institute of Marine Science

Marine diseases are increasing in significance as anthropogenic pressures on the marine environment intensify, yet the factors underlying these disease increases are seldom fully understood. Dermo disease caused by protozoan parasite Perkinsus marinus in the eastern oyster Crassostrea virginica is the unusual case of an established disease that was relatively innocuous but which became markedly worse in a short period of time. Dermo historically was a chronic disease of oysters from southern estuaries, but one causing only modest damage to oyster populations. The situation changed suddenly in the mid-1980s, when dermo greatly intensified in Chesapeake Bay before spreading to Delaware Bay and northeastern systems beginning in 1990. The worsening of dermo disease in Chesapeake Bay was attributed to the effects of multi-year drought creating conditions increasingly favorable for the parasite; the migration north, to warming seawater temperatures. Emerging evidence, however, suggests than an entirely different factor may have been critical: the appearance of a hypervirulent parasite phenotype that caused far higher levels of infection and disease than the parasite form that was originally present. Carnegie will explore the evidence for rapid evolution of hypervirulence in this important oyster pathogen that was uncovered by reopening the "cold case" of dermo disease, and consider some unexpected influences that could well be behind this parasite's rise.