Viral hemorrhagic septicemia (VHS) is a virus-induced disease that causes hemorrhaging in fish.
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Wildlife at risk
Viral hemorrhagic septicemia affects more than 65species of saltwater and freshwater fish in several Northern Hemisphere countries. It affects fish of all ages and sizes.
There are four groups of viral hemorrhagic septicemia virus (I, II, III, IV). These are located in distinct geographic areas. GroupsI, II and III are found mainly in Europe, while group IV is present in North America and Asia. The susceptibility of fish species to the virus differs in each group.
In Canada, the virus has been found on the Pacific coast, the Atlantic coast and in the Great Lakes. It has never been recorded in Québec.
In the Great Lakes, at least 28species of fish are known to be susceptible to this virus. The species that are most affected are muskellunge (in French only), largemouth bass (in French only) and yellow perch (in French only). Salmonids (trout and salmon) should be less susceptible to the virus group present in this region.
Signs of the disease’s presence
Fish infected with viral hemorrhagic septicemia may have several symptoms:
bulging eyes;
bleeding around the eyes and at the base of the fins;
discoloured gills;
darkening of the body;
protruding belly due to fluid accumulation in the abdominal cavity;
corkscrew swimming behaviour.
Fish can also carry the disease without having any physical manifestations.
Viral hemorrhagic septicemia is a systemic (generalized) disease, as the virus spreads through the blood throughout the fish's body and affects a multitude of organs. This makes it difficult to distinguish it from other systemic diseases, whether of viral or bacterial origin.
Transmission and persistence in the environment
Viral hemorrhagic septicemia is transmitted between fish through direct contact, predation of infected prey, or contact with contaminated water, including urine and sexual secretions. Depending on the temperature, the virus can survive in water for several days. Cold water from 2°C to 15°C is particularly good for survival. It enters fish through the gills and possibly through injuries on the body’s surface.
Several elements contribute to the spread of the virus:
the natural movement of fish;
the transfer of infected fish (bait fish, stocking, etc.);
the transfer of contaminated water (ballast water, fish transport water, etc.);
the use of contaminated equipment.
Fish-eating birds can also transport infected fish to uncontaminated sites. However, there is no transmission through their feces due to their high body temperature and acidity of their digestive system.
Treatment
There is no cure for this contagious disease that causes the death of infected fish.
Protection and prevention
Québec’s bodies of water are environments conducive to the introduction and spread of the viral hemorrhagic septicemia virus. Cold temperatures during most of the year and the presence of vulnerable species are ideal conditions for its establishment. You can prevent its introduction and spread by applying several simple measures such as:
Not moving live or dead fish from one body of water to another.
Disposing of unused bait fish and carcasses of harvested fish in the trash.
In the Great Lakes region, the viral hemorrhagic septicemia virus has been associated with several episodes of mass fish die-offs affecting at least 14species.
Risk for human health
Viral hemorrhagic septicemia has no impact on human health. However, it should be noted that the consumption of fish that appear ill, dying or that are found dead should be avoided, since this could entail other health risks. Furthermore, adopting some safe practices when preparing and cooking wild fish always remains relevant.
Surveillance and control
To date, no cases of viral hemorrhagic septicemia have been reported in Québec. In the years following episodes of fish mortalities caused by the virus in the Great Lakes, targeted monitoring campaigns were conducted in Québec. Details are available in the following documents (in French only):