Morphology and morphogenesis of infectious salmon anaemia virus replicating in the endothelium of Atlantic salmon Salmo salar

Abstract

Thin section electron microscopy of tissues from farmed Atlantic salmon Salmo salar L. with clinical infectious salmon anaemia revealed virus budding from endothelial cells. The typical enveloped virus particle showed a regularly arranged filamentous nucleocapsid and a matrix protein-like structure. Virus was budding from the plasma membrane, mainly at the luminal side, and also from certain intracellular membranes. Morphology and morphogenesis resembled orthomyxoviruses. In addition to the typical spherical particles (diameter 100 nm), defective particles, filamentous particles, tubular membrane projections and cytoplasmic nucleocapsid inclusions were observed. Lysis of virus producing cells was infrequently found and was associated with excessive formation of viral structures.