Fish Virus In The Great Lakes Causing Concern

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Main Category: Veterinary
Also Included In: Water - Air Quality / Agriculture;  Infectious Diseases / Bacteria / Viruses
Article Date: 15 May 2007 - 5:00 PDT

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Media reports coming in from towns in and around the Great Lakes in North America are expressing concern about the spread of a deadly fish virus called viral hemorrhagic septicemia (VHS) that is thought to have killed large numbers of fish in the past few years. The virus is not harmful to humans.

Fish experts from the Department of Natural Resources in Wisconsin have conducted tests on two fish found from Little Lake Butte des Morts near Oskosh that suggest the virus is beginning to spread to inland waters.

VHS is a highly contagious pathogen that infects fresh and saltwater fish and causes them to bleed to death internally.

It has been found in several of the Great Lakes and tributaries and is thought to be behind the large scale die offs of fish populations in those waters in recent years. As well as the worrying impact on wildlife and ecosystems of millions of fish dying from the dreadful disease, it is feared that if the virus spreads it could do significant damage to the local economy and leisure industry.

The authorities are urging people fishing and boating in the area to be extra careful with equipment cleanliness, bait disposal and movement of live fish. For instance, these points were made by the Sheboygan Press in Wisconsin earlier today:

• Never move fish eggs or live fish to other waters.
• Buy bait only from recognized local dealers.
• Clear aquatic plants, animals and mud from your boat, trailer and equipment before you leave.
• Drain the water from your boat, motor, bilges, live wells and bait containers before you leave.
• Don't throw left over unwanted bait in the water.
• Rinse your boat and any other equipment that has been in the water with hot water, or dry it for at least five days.
• If you see large numbers of dead fish or find any with blood spots, report it to the local DNR representative or conservation warden.

it is not known how the disease arrived in the Great Lakes. It was first detected in Lake Ontario in 2005 although research suggests it was in Lake St Clair two years before that. Before being detected in the Great Lakes it was believed that VHS was confined to saltwater finfish in the Atlantic and Pacific. It is likely that the virus in the Great Lakes is a new strain of VHS.

In October last year the US Department of Agriculture's (USDA) Animal and Plant Health Inspection Service (APHIS) issued a federal order banning the importation into the US of 37 species of live fish from two provinces in Canada. The order also banned the movement of the same types of fishes among the 8 US states that surround the Great Lakes.

This month the federal order was revised to allow "catch and release" of the 37 species of fish in waters that traverse the state and national boundaries because it is now thought that this activity does not significantly increase the spread of the virus. Catch and release fishing does not involve moving VHS vulnerable fish from place to place; the fish are returned to the water they are caught in. Neither are they used as live bait.

The relaxation of the order will now allow many recreational activities that are very popular in the region to proceed, such as tournaments, fishing derbies, competitions, and anglers who just want to do some catch and release fishing.

VHS causes hemorraghing and death in over 37 species of fish including various kinds of trout, cod, herring, salmon, perch and pike. Some fish show little external signs of infection, while others develop bulging eyes and bloated abdomens, while hemorrhaging from the eyes, gills and base of the fins may also occur.

Fish with VHS can also develop lesions that can be misread as symptoms of other infections, so the only definitive way to diagnose the disease is through testing.

The virus spreads from fish to fish through urine and other fluids that are released into the water where it can survive for two weeks. It can also spread as fish eat other infected fish. Also, the water-borne virus invades a new host through the gills and within 48 hours is being shed again. Even fish that survive the infection and have developed antibodies can shed the virus and spread it to other fish.

Click here for more information about VHS in fish and the details behind the Federal Order (from USDA, requires PDF reader).

Written by: Catharine Paddock
Writer: Medical News Today
Copyright: Medical News Today
Not to be reproduced without permission of Medical News Today

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