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Intensification Breeds Infection
Image: Salmon by smalljude CC BY 2.0
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Pilchard Orthomyxovirus (POMV) = Herpes
One of the worst diseases that can infect farmed salmon is what is known as Pilchard Orthomyxovirus (POMV). It is a type of Herpes virus [1]. Don't worry, there is no indication that you may catch herpes from eating salmon that have it. (Whether you want your salmon to have herpes is another issue.)
POMV is one nasty virus. In late May 2018, a report came to light that more than 1.35 million farmed salmon had died in the previous six months due to POMV [2]. So then, you may be wondering, what the heck is POMV, where did it come from, can it hurt people, and what is being done about it. Let's unpack that.
What is POMV?
POMV is a type of virus that is highly lethal to fish. It is passed between wild fish and farmed salmon, and while incubating and potentially mutating in the fertile cauldron of opportunity that salmon farms offer, may then be passed back to wild fish [3].
Where did POMV come from?
POMV first came to light in two unprecedented pilchard mortality events in 1995 and 1998-1999 across southern Australia [4]. The causative agent in these two events was a herpes virus, which infected the gills and led to asphyxiation.
Pilchards are a type of small, silvery, oily fish known as 'forage fish' or 'small pelagic fish'. They are in the herring family variously interchangeable with sardines.
Can people catch POMV or Herpes from eating salmon?
No. There is no evidence that we can catch this disease from eating salmon. However, it is a virulent disease and it is possible that it could affect the quality of the fish we buy if infected fish are sold to market.
How do fish catch POMV?
Recent research led by CSIRO found that POMV can be caught from virus-contaminated seawater, and that fish do not need to be in direct contact with diseased fish to become infected [5].
What is being done to protect fish from POMV?
Currently there is no vaccine and no treatment for POMV in salmon. This is an active area of research.
Protecting fish from POMV is about more than just salmon. The threat of disease transfer from salmon to pilchards reverberates well beyond pilchards. Because of the ubiquity of pilchards as a food source, their absence can impact up the food chain. Pilchards are a commonly available, high-energy food source for marine mammals and seabirds. While many predator species naturally have a varied diet, in the absence of pilchards they may nonetheless have to exert greater foraging effort to compensate for catching lower-energy prey. Pilchards are also an economically important fishery in Australia, so any downturn in their population will almost invariably impact on fishermen's livelihoods.
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