Pilchard Orthomyxovirus

Pilchard Orthomyxovirus was first discovered in Australia in 1998 in pilchards (Sardinops sagax) in South Australia[1]. At that time, there were largescale deaths of pilchards caused by a herpes virus and, while testing, Pilchard Orthomyxovirus was also found to be present in these fish. Infected pilchards are usually just show subclinical symptoms, but signs of disease and mortalities in salmons have been recorded.

However, this was simply an accidental finding by diagnostic tests as these pilchard weren't dying from Pilchard Orthomyxovirus. This virus probably has been in pilchards for a very long time.

Pilchard Orthomyxovirus has been detected in pilchards and Atlantic salmon in Australia in 1998 and then went off the radar. It was rediscovered in 2006 in Tasmanian waters in Atlantic salmon on the Tamar River. The first outbreak of Pilchard Orthomyxovirus in Atlantic salmon occured  in 2012 in the south east of Tasmania.

As pilchards are small enough to swim through the nets on salmon farms, and salmon are susceptible to the virus, it can be passed from pilchards to salmon, salmon to salmon, and potentially salmon to pilchards.

Pilchard Orthomyxovirus is distantly related to the Infectious Salmon Anaemia Virus, which causes disease in Atlantic salmon on both sides of the Atlantic Ocean. However, as a result of the observed differences, Pilchard Orthomyxovirus is the first virus to be characterised from a new genus within the Orthomyxoviridae[2].

As is the case with Pilchard Orthomyxovirus, Infectious Salmon Anaemia virus causes disease in Atlantic salmon, but does not cause disease in herring, brown trout, or other fish species.

[1] Pilchard Orthomyxovirus (POMV) fact sheet. See here.
[2] Mohr et al: Pilchard Orthomyxovirus (POMV). I. Characterisation of an Emerging Virus Isolated From Pilchards Sardinops Sagax and Atlantic Salmon Salmo Salar in Diseases of Aquatic Origin - 2020