Viral hemorrhagic septicemia ; Deadly fish virus lurks off Oregon Coast
Initial Article From : Henry Miller; Statesman Journal (edited)
“Officials in the Pacific Northwest are worried that a fish virus that causes fish kills in the Great Lakes could get here.
In a sense, it's already here and has been for quite a while. Viral hemorrhagic septicemia, better known as VHS, has been found in ocean fish (mostly salmonids) from Coos Bay north to the Gulf of Alaska.
The seagoing strain of the virus, which does not affect humans, has devastated herring schools in Puget Sound near Seattle and Prince William Sound. And an apparently new mutated freshwater strain has done the same in the Great Lakes, killing fish from minnows to muskies.
"What seems to be the case is these marine strains don't seem to come ashore very readily. And they've had plenty of opportunity with migrating salmon," said Jim Winton, the chief of the Fish Health Section of the USGS Western Fisheries Research Center in Seattle."We occasionally find the marine strain of VHS in a spawning salmon, mostly coho," he added. "But it doesn't seem to have spread to freshwater species."
The species that VHS infects that are shared by the Great Lakes and the Pacific Northwest include yellow perch, small mouth bass, walleye, bluegill, crappie, lake trout, steelhead and Chinook salmon.
It takes a week to 15 days of incubation in infected fish. Symptoms can range from no outward appearance to pale gills, bulging eyes, bleeding around the eyes, fins and sides of the head and behavioral changes such as swimming in a spiral.
Internally, the liver, spleen and intestines can be clotted with bleeding sores, the signs of which can include a bloated-looking, fluid-filled abdomen. It kills in days. And fish that survive become viral carriers for the rest of their lives. Stress is one factor that can trigger outbreaks, which is why hatchery, net-pen and fish-transport crowding can accelerate the spread.
Fish (most commonly salmonids such as Salmon & Trout) that become infected will often be anorexic and show hemorrhaging of their internal organs, skin, and muscle; however they may be no external symptoms, while other fish show signs of infection that include bulging eyes, bloated abdomens, bruised-looking reddish tints to the eyes, skin, gills and fins. External signs may include dark coloration, “pop eye” (exophthalmia), pale or red-dotted gills, sunken eyes, and bleeding around the eye sockets and at base of fins
While still alive, fish with Viral hemorrhagic septicemia (VHS) may appear listless or limp, hang just beneath the surface, or swim very abnormally, such as constant flashing circling due to the growth or turning movement (tropism) of the virus in the brain.
Septicemia is a symptom of different pathogens with basically the same result: a poisoning of the blood. It is common in aquariums where the usual cause is the very common anaerobic gram negative bacteria, Aeromonas. In aquariums and pond Septicemia is more common when conditions are poor with overabundance of decomposition and decay along with poor circulation, low oxygen levels and low GH/electrolyte levels
* Viral hemorrhagic septicemia; pdf
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