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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