Fletcher et al. (1997) suggest that the size of the outbreak in 1995 are consistent with infection of a naïve Australian pilchard population by an exotic herpes virus to which they had never previously been exposed. The use of imported pilchards to feed caged southern bluefin tuna in South Australian waters provides a potential source of such a virus. This is one explanation that highlights the need for a panel of diagnostic reagents and tests to screen imported pilchards for the presence of the herpes virus.
Herpes viruses are well-known to cause latent infections whose existence remains unknown until a predisposing environmental factor leads to their recrudescence. The factor most commonly recognised in virus reactivation is stress tha tcan itself be induced by a variety of stimuli including infection by another, unrelated microorganism. Fletcher et al. (1997) suggest that the severity of the disease observed in Australian pilchards and its emanation from a single geographic locality are not consistent with reactivation of a latent infection. However, we can not at this time rule out the possibility that the herpes virus is endemic and present in a latent state in Australian pilchards and is activated following infection by and, as yet, unidententified microorganism that spreads from a point source in South Australia. Imported pilchards may or may not be the source of such microorganism. There is a need to rule out involvement of other microorganisms in the death of the pilchards and to use the panel of diagnostic reagients and tools mentioned above to determine if Australian pilchards are latently infected by a herpes virus. Mortalities observed in the juvenile fish populuation in 1998 but not in 1995 raise questions about the role of herpes virus in the recent outbreak. There is a need to determine if herpes virus is present in dead juvenile fish.
Fletcher. W.J., Jones, B., Pearce, A.F. and Hosja (1997). Environmental and biological aspects of the mass mortality of pilchards (Autumn 1995) in Western Australia. Fisheries Research Report No 106, Fisheries Department of Western Australia.
