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.

Ryan Carnegie received a B.A. degree from Rutgers University and M.A. from the College of William & Mary (Virginia Institute of Marine Science) before completing a Ph.D. at the University of Maine and post-doctoral appointments at the Pacific Biological Station (Nanaimo, British Columbia) and the Medical University of South Carolina. He has been on the faculty of the Virginia Institute of Marine Science since 2010, where is he now a Research Associate Professor. He is a marine parasitologist and pathologist whose research focuses primarily on the evolutionary ecology of marine diseases and the phylogenetics and phylogeography of protozoan parasites.

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