Pacific Salmon Paramyxovirus

VIRUSES Pacific Salmon Paramyxovirus

I. Causative Agent and Disease This virus has the unique characteristic Pacific salmon paramyxovirus among fish viruses of hemagglutinating (PSPV) is a large, irregular shaped, erythrocytes from fish, some mammals enveloped, single-stranded RNA virus (human, rabbit, horse, guinea pig and about 125-250 nm in diameter belonging swine), and birds. Hemagglutination in the family Paramyxoviridae and the allows viral placement in the Paramyxo- genus Aquaparamyxovirus. The virus is viridae and confirmation of a para- of low virulence and not associated with myxovirus along with other procedures disease or mortality. The viral agent is including ultrastructural morphology generally isolated from asymptomatic by electron microscopy, fluorescent an- carrier fish during routine viral screen- tibody testing (FAT), PCR and sequenc- ing. ing.

II. Host Species VI. Prognosis for Host The most common host in North The prognosis for the host is good America is adult Chinook salmon from regarding the non-pathogenic nature of Alaska, Oregon and Washington. Un- the North American isolates of PSPV. confirmed isolates have been reported The role of Norwegian ASPV in causing from other salmonids. In Norway, At- PGI is questionable since other agents lantic salmon paramyxovirus (ASPV) have been present confounding the has been isolated from seawater reared true etiology of fish mortality. In this Atlantic salmon. case perhaps corrective therapy would include optimizing the environment and III. Clinical Signs avoidance. Further study is warranted. No clinical signs of disease are associated with fish infected by PSPV. VII. Human Health Signifcance The ASPV paramyxovirus in Norway is There are no human health concerns reportedly associated with the disease associated with paramyxoviruses in fish. syndrome, proliferative gill inflamma- tion (PGI).

IV. Transmission The mode of transmission is hori- zontal by water or fish to fish. A marine reservoir for the virus is suspected.

V. Diagnosis Detection of paramyxovirus is by isolation in cultures of susceptible fish cell lines inoculated with infected tissue. The virus causes a cytopathic effect (CPE) characterized by retracted and rounded cells after an extensive incuba- tion period. Presumptive identifications are made by observing the typical CPE.

VIRUSES 

Chinook salmon, Ninilchik River, AK. Falsely colorized ultrastructure of PSPV in cultured infected CHSE-214 cell with three virus particles in diferent stages of budding from cell membrane (arrow = center particle); blue (B) = spiked envelope; purple (P) = nucleocapsid within particles from pool of subsurface nucleocapsid material in the cytoplasm. Inset: Same image not colorized. (From Meyers and Batts 2016).

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Cytopathic efect of PSPV from Chinook salmon, Ninilchik River, AK in CHSE-214 cells at 14°C demonstrating clustered rounding and refractility of cells (Right) at 9 days post- inoculation of previously passaged material. Normal cell culture (Left). Phase contrast (From Meyers and Batts 2016).