Heart and skeletal muscle inflammation (HSMI) and cardiomyopathy syndrome (CMS) are putative viral cardiac diseases of Atlantic salmon. This study examined the levels and correlated the serum enzymes creatine kinase (CK) and lactate dehydrogenase (LDH) to the histopathology of clinical outbreaks of HSMI and chronic CMS in farmed Atlantic salmon. A total of 75 fish from 3 different HSMI outbreaks, 30 chronic CMS fish, and 68 fish from 3 nondiseased fish groups were used as the study population (N = 173). Serum CK and LDH levels correlated significantly with the total inflammation and total necrosis scores for HSMI fish (P = 0.001). However, no correlation was identified for enzyme levels and histopathology scores for chronic CMS fish. The significantly increased CK and LDH levels and their positive correlations to histopathology differentiate HSMI from CMS clinically suggesting the potential use of enzymes for screening for HSMI is promising.
Salmonid alphavirus (SAV) is the most divergent member of the family Togaviridae and constitutes a threat to farming of salmonid fish in Europe. Here, we report cloning, expression and preliminary functional analysis of the capsid protein of SAV, confirming it to be expressed as an approximately 31-kDa protein in infected cells. The protein localizes strictly to the cytoplasm in Chinook salmon embryo cells, and either to the nucleus or cytoplasm in bluegill fry cells. An expression study of full-length and different truncated versions of the SAV capsid fused to the enhanced green fluorescent protein demonstrated that the localization is independent of other viral components in both cell lines, and controlled by the N-terminal 82 aa, which include a conserved, predicted helix and a downstream positively charged region. Thus, the results suggest that the SAV capsid possesses a cell-type-dependent potential for nuclear import and export. Moreover, the SAV capsid and its N-terminal 82 aa were shown to be associated with inhibition of cellular proliferation, a hallmark of the cytopathic effect caused by SAV. These results highlight that the SAV capsid is a multifunctional protein with possible importance for pathogenesis.
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