The infectious salmon anemia virus esterase prunes erythrocyte surfaces in infected Atlantic salmon and exposes terminal sialic acids to lectin recognition

Many sialic acid-binding viruses express a receptor-destroying enzyme (RDE) that removes the virus-targeted receptor and limits viral interactions with the host cell surface. Despite a growing appreciation of how the viral RDE promotes viral fitness, little is known about its direct effects on the host. Infectious salmon anemia virus (ISAV) attaches to 4-O-acetylated sialic acids on Atlantic salmon epithelial, endothelial, and red blood cell surfaces. ISAV receptor binding and destruction are effectuated by the same molecule, the haemagglutinin esterase (HE). We recently discovered a global loss of vascular 4-O-acetylated sialic acids in ISAV-infected fish. The loss correlated with the expression of viral proteins, giving rise to the hypothesis that it was mediated by the HE. Here, we report that the ISAV receptor is also progressively lost from circulating erythrocytes in infected fish. Furthermore, salmon erythrocytes exposed to ISAV ex vivo lost their capacity to bind new ISAV particles. The loss of ISAV binding was not associated with receptor saturation. Moreover, upon loss of the ISAV receptor, erythrocyte surfaces became more available to the lectin wheat germ agglutinin, suggesting a potential to alter interactions with endogenous lectins of similar specificity. The pruning of erythrocyte surfaces was inhibited by an antibody that prevented ISAV attachment. Furthermore, recombinant HE, but not an esterase-silenced mutant, was sufficient to induce the observed surface modulation. This links the ISAV-induced erythrocyte modulation to the hydrolytic activity of the HE and shows that the observed effects are not mediated by endogenous esterases. Our findings are the first to directly link a viral RDE to extensive cell surface modulation in infected individuals. This raises the questions of whether other sialic acid-binding viruses that express RDEs affect host cells to a similar extent, and if such RDE-mediated cell surface modulation influences host biological functions with relevance to viral disease

Infeksjoner med parasitten Nucleospora cyclopteri (Microsporidia) i rognkjeks, Cyclopterus lumpus

Source at https://www.vetinst.no/rapporter-og-publikasjoner/rapporter/2019/infeksjoner-med-parasitten-nucleospora-cyclopteri-microsporidia-i-rognkjeks-cyclopterus-lumpus.Nucleospora cyclopteri (Microsporidia) is one of many parasites infecting lumpfish, Cyclopterus lumpus, and has been shown to cause disease and mortality in lumpfish. Infections in fish are often multifactorial and the impact of one agent on the development of disease can be difficult to elucidate. In addition to mortality, infections in lumpfish can lead to diseases with subsequently lowered appetite. This is of particular importance since lumpfish are used as a biological control agent, eating salmon lice, Lepeophtherius salmonis, off the salmon. Knowledge on the different disease agents of lumpfish is therefore of utmost importance. The main aim of this project was to identify how to obtain an infection-free lumpfish in land-based hatcheries and to study the impact that N. cyclopteri has on the health of the lumpfish and thereby its effect as a biological control agent. The project therefore aimed to map the presence of N. cyclopteri and other disease agents in wild caught lumpfish and in eggs/sperm, in fry and in farmed lumpfish stocked in the sea. In addition, we wanted to study the transmission pathways and clinical significance of the parasite. Unfortunately, we were not able to obtain a group of lumpfish fry infected with N. cyclopteri that we intended to follow through the land phase. The study of pathogenesis, infection dynamics, or whether an infection with N. cyclopteri pre-disposes for secondary infections, was therefore abandoned. We studied the presence of co-infections, methods for optimal sampling and tissue tropism in wild caught lumpfish in this project. Nucleospora cyclopteri was present in 60% of the sampled individuals from the waters around Averøy, in county Møre og Romsdal. The fish were analysed with regard to a range of infectious agents (viruses, bacteria and parasites) commonly found in other fish species, or previously recorded in lumpfish. No viral agents or other important pathogens were detected, but supposedly nonpathogenic microparasites, like Kudoa islandica (Myxozoa) in the muscle tissue and coccidians in the intestine, were frequently found. Nucleospora cyclopteri was detected in all tissues examined: anterior, mid and posterior kidney, spleen, heart, gills, brain, muscle liver and blood, thus indicating that the infection is systemic. The density of N. cyclopteri was highest in the anterior kidney, followed by mid and posterior kidney, spleen and gills, while the prevalence was highest in the ventricle of the heart. Observations from this study indicate that the parasite is released through urine and bile. We also show that N. cyclopteri can be detected using swabs from the skin, gill and vent, and by blood samples and gill biopsies, thus demonstrating the possibility of non-lethal detection of N. cyclopteri in lumpfish. Amongst these, the most promising non-lethal samples for detection were gill biopsies and leukocyte fractions from blood samples. Images normal histology and pathological agents from this project is included in an openly available online image database. This image database can be accessed by diagnosticians and researchers and used when evaluating pathological findings in lumpfish. While vertical transmission cannot be excluded, the results from this project indicate that this is not the dominant route. It is in any case advisable to routinely screen broodfish for N. cyclopteri to avoid using positive individuals for the production of eggs and fry. Given that N. cyclopteri undoubtedly destroys leukocytes in high numbers and over large areas of tissue, it is reasonable to assume that the parasite has an effect on the immune competence of the fish

Development and characterization of two cell lines from gills of Atlantic salmon

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Development and evaluation of a method for concentration and detection of salmonid alphavirus from seawater

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