Bulletin of the Aquaculture Association of Canada 104 2 71 78 St. Andrews, Canada: Aquaculture Association of Canada.

Infectious salmon anaemia (ISA) virus (ISAV) is currently one of the most important viral pathogens threatening commercial aquaculture in the northern hemisphere. The virus is classified in the family Orthomyxoviridae, genus Isavirus. The virus offers a significant challenge to fish biologists interested in diagnosis and control of ISA, and to molecular virologists because of its evolutionary relationship with influenza viruses. Being an orthomyxovirus, ISAV is expected to be prone to genetic and antigenic variation. However, while the ISAV genome, like the influenza A virus genome, encodes at least nine structural proteins, the gene order and putative functional identities of the ISAV proteins are significantly different from those of influenza viruses. Although the virulence of influenza A viruses is a polygenic trait, one virulence factor is correlated with the haemagglutinin cleavage site. It remains to be shown which genetic variations in ISAV are associated with the virulence of the virus. The ability of ISAV to kill rainbow trout is a correlate of ISAV pathogenicity that might facilitate the identification of ISAV virulence genes.

Avian Diseases 31 3 654 657 UNITED STATES

The lesions and etiologic agents associated with 13 outbreaks of respiratory disease in commercial chickens were investigated. Adenoviruses were isolated from tracheal and lung tissues of affected chickens in all 13 outbreaks. Escherichia coli was isolated from the lung of an occasional bird. The tracheal specimens were consistently negative for Bordetella avium, but E. coli and occasionally Staphylococcus aureus were isolated. There was also serological evidence in one outbreak, and pathological evidence in another, of a concurrent infectious bursal disease virus (IBDV) infection of chickens affected with the disease. Gross and microscopic alterations in the tracheas and lungs of affected chickens were similar in all outbreaks and consisted of catarrhal tracheitis and occasionally multifocal pneumonia with mononuclear cell infiltrates. Hepatitis and splenitis with heterophil infiltrates occasionally were seen in birds with coliform septicemia. The tracheal and lung lesions in the present investigation were considered primarily of adenovirus etiology, complicated by secondary bacterial infection

Antibodies to infectious salmon anaemia virus (ISAV) augment virus entry in macrophage-like fish cell lines

Infectious salmon anaemia virus (ISAV), a member of the family Orthomyxoviridae, is an important fish pathogen in marine aquaculture in the Northern Hemisphere. The pathogenesis of ISAV infection at the cellular level is not well studied. We investigated three permissive cell lines for ISAV, (SHK-1, TO and CHSE-214) as indicator systems for virus neutralization (VN) with anti-ISAV polyclonal antibodies of rabbit or fish (Atlantic salmon) origin. It was shown that the rabbit antiserum showed higher VN antibody titres in the CHSE-214 cell line than in macrophage-like fish cell lines SHK-1 and TO. With the fish antiserum, VN was observed only on CHSE-214 cells. The input virus used in the CHSE-214 cell system (i.e., 100TCID50) was found to be 1000 and 2000 times more than that used in the SHK-1 and TO cell systems, respectively, indicating that the true VN antibody titres of the antisera used were higher than the titres obtained on CHSE-214 cells. Neutralization of infectious pancreatic necrosis virus (IPNV) by rabbit anti-IPNV polyclonal serum in both CHSE-214 and TO cells demonstrated that effective virus neutralization is possible in TO cells. The VN antibody titre of rabbit anti-ISAV serum was increased 48-fold in TO cells when the assay was performed in presence of staphylococcal Protein A, which binds to the Fc moiety of immunoglobulins. Antibody-facilitated entry of ISAV in TO cells was confirmed using fluoresceine isothiocyanate (FITC)-labelled ISAV and rabbit anti-ISAV serum. These findings indicate that antibodies to ISAV augment the virus infection of macrophage-like fish cells. In conclusion, this study has demonstrated, for the first time, possible Fc receptor-mediated infection of macrophage-like fish cell lines by a fish virus, ISAV.

Bulletin of the Aquaculture Association of Canada 104 2 90 96 St. Andrews, Canada: Aquaculture Association of Canada.

The current understanding on the pathogenesis and the mechanism of persistence of ISAV in fish is limited. Three permissive fish cell lines SHK-1, CHSE-214 and TO were used to determine if the cytopathic effect (CPE) observed in ISAV isolate NBISA01 and U5575-1 infection is due to apoptosis or necrosis. Apoptosis was observed only in SHK-1 and CHSE-214 infected cells with both isolates. TO cells infected by both isolates did not undergo apoptosis but showed damage characteristic of necrosis. These findings suggest that the mechanism of cell death during ISAV infection is dependent on the cell type. The TO cells were used to study the gene expression of ISAV using New Brunswick isolate-RPC-01-0593-01, Nova Scotia isolate-U5575-1 and Norwegian isolate 810/9/99 and in situ hybridization with ISAV segments 7 and 8 riboprobes. The difference in the frequency of hybridization signals between U5575-1 and the other two isolates was statistically significant (P=0.004), indicating that the pathology associated with ISAV infection in vivo may depend not only on infected cell types but also on the infecting ISAV isolate.