A VIRUS likened to the human Ebola virus because it makes fish bleed to death has been identified as the mystery agent that caused thousands of dead fish to clog up Milwaukee harbour last month.
Fish virologists at the DNR say that after regularly causing die-offs in at least 25 species in the Great Lakes since it first hit in 2003, the disease hadn’t struck since 2008.
They believe VHS vanished because fish that survived the first outbreaks became immune to it. But fish born more recently would not have had any exposure and would therefore lack immunity, causing another die-off. The DNR researchers think this is what happened in Milwaukee.
“The gizzard shad infected with VHS in March were hatched in the summer of 2010, and so were naive to the virus,” says Susan Marcquenski of the DNR. Because the lakes are so large, die-offs may occur undetected, but the spectacular and unexpected deaths in the harbour made it easier to identify and diagnose.
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