Abstract
All viruses infecting fish must cross the surface mucosal barrier to successfully enter a host. Infectious salmon anaemia virus (ISAV), the causative agent of the economically important infectious salmon anaemia (ISA) in Atlantic salmon, Salmo salar L., has been shown to use the gills as its entry point. However, other entry ports have not been investigated despite the expression of virus receptors on the surface of epithelial cells in the skin, the gastrointestinal (GI) tract and the conjunctiva. Here we investigate the ISAV mucosal infection in Atlantic salmon after experimental immersion (bath) challenge and in farmed fish collected from a confirmed outbreak of ISA in Norway. We show for the first time evidence of early replication in several mucosal surfaces in addition to the gills, including the pectoral fin, skin and GI tract suggesting several potential entry points for the virus. Initially, the infection is localized and primarily infecting epithelial cells, however at later stages it becomes systemic, infecting the endothelial cells lining the circulatory system. Viruses of low and high virulence used in the challenge revealed possible variation in virus progression during infection at the mucosal surfaces.Electronic supplementary materialThe online version of this article (doi:10.1186/s13567-015-0265-1) contains supplementary material, which is available to authorized users.
Highlights
Infectious salmon anaemia (ISA), caused by the ISA virus (ISAV) [1] is an important disease of farmed Atlantic salmon, Salmo salar L., and listed as notifiable by the OIE
The present study investigated the significance of mucosal infection for ISA pathogenesis by revealing alternative entry routes and sites of early viral replication other than the gills
We demonstrate for the first time that Infectious salmon anaemia virus (ISAV) was taken up and replicated in mucosal surfaces other than gills, such as the pectoral fin, skin and GI tract
Summary
Infectious salmon anaemia (ISA), caused by the ISA virus (ISAV) [1] is an important disease of farmed Atlantic salmon, Salmo salar L., and listed as notifiable by the OIE. First reported in Norway in 1984, the prevalence peaked in the 90s, resulting in the implementation of strict biosecurity measures to combat the disease [2]. ISA has caused significant problems in Scotland, the Faroe Islands, Chile, and on the east coast of Canada and USA. Without any intervention, accumulated fish mortality may reach 80% over several months [3]. Anaemia, haemorrhaging in the eyes and skin, pale gills, ascites, dark liver and swollen spleen are common signs in diseased fish suggesting circulatory failure as a major mechanism of pathogenesis (reviewed in [4])
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