A novel totivirus and piscine reovirus (PRV) in Atlantic salmon (Salmo salar) with cardiomyopathy syndrome (CMS)

<p>Abstract</p> <p>Background</p> <p>Cardiomyopathy syndrome (CMS) is a severe disease affecting large farmed Atlantic salmon. Mortality often appears without prior clinical signs, typically shortly prior to slaughter. We recently reported the finding and the complete genomic sequence of a novel piscine reovirus (PRV), which is associated with another cardiac disease in Atlantic salmon; heart and skeletal muscle inflammation (HSMI). In the present work we have studied whether PRV or other infectious agents may be involved in the etiology of CMS.</p> <p>Results</p> <p>Using high throughput sequencing on heart samples from natural outbreaks of CMS and from fish experimentally challenged with material from fish diagnosed with CMS a high number of sequence reads identical to the PRV genome were identified. In addition, a sequence contig from a novel totivirus could also be constructed. Using RT-qPCR, levels of PRV in tissue samples were quantified and the totivirus was detected in all samples tested from CMS fish but not in controls. <it>In situ </it>hybridization supported this pattern indicating a possible association between CMS and the novel piscine totivirus.</p> <p>Conclusions</p> <p>Although causality for CMS in Atlantic salmon could not be proven for either of the two viruses, our results are compatible with a hypothesis where, in the experimental challenge studied, PRV behaves as an opportunist whereas the totivirus might be more directly linked with the development of CMS.</p

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

First detection of piscine reovirus (PRV) in marine fish species

Heart and skeletal muscle inflammation (HSMI) is a disease that affects farmed Atlantic salmon Salmo salar L. several months after the fish have been transferred to seawater. Recently, a new virus called piscine reovirus (PRV) was identified in Atlantic salmon from an outbreak of HSMI and in experimentally challenged fish. PRV is associated with the development of HSMI, and has until now only been detected in Atlantic salmon. This study investigates whether the virus is also present in wild fish populations that may serve as vectors for the virus. The virus was found in few of the analyzed samples so there is probably a more complex relationship that involves several carriers and virus reservoirs

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

publishedVersio

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

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

publishedVersio