First detection, isolation and molecular characterization of infectious salmon anaemia virus associated with clinical disease in farmed Atlantic salmon (Salmo salar) in Chile

<p>Abstract</p> <p>Background</p> <p>Infectious salmon anaemia (ISA) is a viral disease of marine-farmed Atlantic salmon (<it>Salmo salar</it>) caused by ISA virus (ISAV), which belongs to the genus <it>Isavirus</it>, family <it>Orthomyxoviridae</it>. The virus is considered to be carried by marine wild fish and for over 25 years has caused major disease outbreaks in marine-farmed Atlantic salmon in the Northern hemisphere. In the Southern hemisphere, ISAV was first detected in Chile in 1999 in marine-farmed Coho salmon (<it>Oncorhynchus kisutch</it>). In contrast to the classical presentation of ISA in Atlantic salmon, the presence of ISAV in Chile until now has only been associated with a clinical condition called Icterus Syndrome in Coho salmon and virus isolation has not always been possible. During the winter of 2007, unexplained mortalities were registered in market-size Atlantic salmon in a grow-out site located in Chiloé in Region X of Chile. We report here the diagnostic findings of the first significant clinical outbreak of ISA in marine-farmed Atlantic salmon in Chile and the first characterization of the ISAV isolated from the affected fish.</p> <p>Results</p> <p>In mid-June 2007, an Atlantic salmon marine farm site located in central Chiloé Island in Region X of Chile registered a sudden increase in mortality following recovery from an outbreak of Pisciricketsiosis, which rose to a cumulative mortality of 13.6% by harvest time. Based on the clinical signs and lesions in the affected fish, and laboratory tests performed on the fish tissues, a confirmatory diagnosis of ISA was made; the first time ISA in its classical presentation and for the first time affecting farmed Atlantic salmon in Chile. Rapid sequencing of the virus-specific RT-PCR products amplified from the fish tissues identified the virus to belong to the European genotype (Genotype I) of the highly polymorphic region (HPR) group HPR 7b, but with an 11-amino acid insert in the fusion glycoprotein, and ability to cause cytopathic effects (CPE) in CHSE-214 cell line, characteristics which make it distinct from common European Genotype ISAV isolates from Europe and North America.</p> <p>Conclusion</p> <p>In conclusion, the present work constitutes the first report of a case of ISA in farmed Atlantic salmon in Chile. The clinical signs and lesions are consistent with the classical descriptions of the disease in marine-farmed Atlantic salmon in the Northern hemisphere. The outbreak was caused by ISAV of European genotype (or Genotype I) of HPR 7b but distinct from common European Genotype ISAV isolates.</p

Finfish and aquatic invertebrate pathology resources for now and the future

Utilization of finfish and aquatic invertebrates in biomedical research and as environmental sentinels has grown dramatically in recent decades. Likewise the aquaculture of finfish and invertebrates has expanded rapidly worldwide as populations of some aquatic food species and threatened or endangered aquatic species have plummeted due to overharvesting or habitat degradation. This increasing intensive culture and use of aquatic species has heightened the importance of maintaining a sophisticated understanding of pathology of various organ systems of these diverse species. Yet, except for selected species long cultivated in aquaculture, pathology databases and the workforce of highly trained pathologists lag behind those available for most laboratory animals and domestic mammalian and avian species. Several factors must change to maximize the use, understanding, and protection of important aquatic species: 1) improvements in databases of abnormalities across species; 2) standardization of diagnostic criteria for proliferative and nonproliferative lesions; and 3) more uniform and rigorous training in aquatic morphologic pathology

Finfish and aquatic invertebrate pathology resources for now and the future

Utilization of finfish and aquatic invertebrates in biomedical research and as environmental sentinels has grown dramatically in recent decades. Likewise the aquaculture of finfish and invertebrates has expanded rapidly worldwide as populations of some aquatic food species and threatened or endangered aquatic species have plummeted due to overharvesting or habitat degradation. This increasing intensive culture and use of aquatic species has heightened the importance of maintaining a sophisticated understanding of pathology of various organ systems of these diverse species. Yet, except for selected species long cultivated in aquaculture, pathology databases and the workforce of highly trained pathologists lag behind those available for most laboratory animals and domestic mammalian and avian species. Several factors must change to maximize the use, understanding, and protection of important aquatic species: 1) improvements in databases of abnormalities across species; 2) standardization of diagnostic criteria for proliferative and nonproliferative lesions; and 3) more uniform and rigorous training in aquatic morphologic pathology

Vaccine-Induced Protection Against Furunculosis Involves Pre-emptive Priming of Humoral Immunity in Arctic Charr

With respect to salmonid aquaculture, one of the most important bacterial pathogens due to high mortality and antibiotic usage is the causative agent of typical furunculosis, Aeromonas salmonicida spp. salmonicida (Asal). In Atlantic salmon, Salmo salar, the host response during infections with Asal is well-documented, with furunculosis outbreaks resulting in significant mortality in commercial settings. However, less is known about the host-pathogen interactions in the emerging aquaculture species, Arctic charr Salvelinus alpinus. Furthermore, there is no data on the efficacy or response of this species after vaccination with commonly administered vaccines against furunculosis. To this end, we examined the immunological response of S. alpinus during infection with Asal, with or without administration of vaccines (Forte Micro®, Forte Micro® + Renogen®, Elanco Animal Health). Artic charr (vaccinated or unvaccinated) were i.p.-injected with a virulent strain of Asal (106 CFUs/mL) and tissues were collected pre-infection/post-vaccination, 8, and 29 days post-infection. Unvaccinated Arctic charr were susceptible to Asal with 72% mortalities observed after 31 days. However, there was 72–82% protection in fish vaccinated with either the single or dual-vaccine, respectively. Protection in vaccinated fish was concordant with significantly higher serum IgM concentrations, and following RNA sequencing and transcriptome assembly, differential expression analysis revealed several patterns and pathways associated with the improved survival of vaccinated fish. Most striking was the dramatically higher basal expression of complement/coagulation factors, acute phase-proteins, and iron hemostasis proteins in pre-challenged, vaccinated fish. Remarkably, following Asal infection, this response was abrogated and instead the transcriptome was characterized by a lack of immune-stimulation compared to that of unvaccinated fish. Furthermore, where pathways of actin assembly and FcγR-mediated phagocytosis were significantly differentially regulated in unvaccinated fish, vaccinated fish showed either the opposite regulation (ForteMicro®), or no impact at all (ForteMicro®Renogen®). The present data indicates that vaccine-induced protection against Asal relies on the pre-activation and immediate control of humoral immune parameters that is coincident with reduced activation of apoptotic (e.g., NF-κB) and actin-associated pathways

Journal of Aquatic Animal Health 13 4 340 346 Bethesda, USA: American Fisheries Society.

The factors affecting the horizontal transmission of infectious salmon anaemia virus (ISAV) among naive Atlantic salmon Salmo salar maintained in freshwater were examined. The ratio of injected to naive cohabitants was varied and mortality was monitored. Whether ISAV transmission in freshwater required contact among salmon was also examined. Pathognomonic histological lesions in fishes infected by injection or cohabitation were compared. In trial 1, duplicate tanks containing 0+25, 2+23, 4+21, 6+19, or 8+17 fishes (injected+naive, respectively) were established. Mean days to onset of mortality and mean days to death (mdd) were significantly less among injected fish (16.9 and 18.8 days, respectively) than in fishes infected by cohabitation (33.4 and 43.8 days). Cumulative mortality in naive cohabitants in trial 1 was significantly greater in groups containing 6 injected fishes compared with those containing either 2 or 8 injected fishes. In trial 2, triplicate tanks of 0+25, 4+21, and 6+19 fish were established. Mean days to onset of mortality and mdd were similar to those in trial 1. Mean cumulative mortalities among naive cohabitants were 93.7 and 93.0% in groups containing 4 and 6 injected fishes, respectively. In trial 3, salmon exposed to water draining from tanks containing infected fishes suffered mortality, and ISAV was detected by reverse transcriptase polymerase chain reaction. Pathognomonic lesions in the gut (stomach, caeca, upper intestine) were significantly more frequent in fishes infected by cohabitation than in those infected by injection. Lesion scores of gut histology were significantly greater in cohabitation-infected fishes than in injected fishes, whereas those of the liver were significantly greater in injected fishes. This study confirmed that ISAV was transmissible among freshwater-reared salmon and that contact among fishes was not required for transmission. The reduced frequency and severity of microscopic gut lesions in fishes infected by injection may have been related to the more rapid pathogenesis associated with this route of infection.

Bulletin of the European Association of Fish Pathologists 18 4 110 114

This report describes the clinical and histopathological features of infectious salmon anaemia virus infection in salt water farmed Atlantic salmon in the Bay of Fundy, New Brunswick, in the late summer of 1997. The virus was isolated from several sites by culture on SHK-1 cells and confirmed by monoclonal indirect fluorescent antibody technique. Gross examination revealed branchial pallor, exophthalmos, external ventral petechial haemorrhage, ascites and congested pyloric caecae, lower intestines and spleens. Microscopic examination was characterized by renal interstitial haemorrhage and tubular necrosis, branchial lamellar and filamental congestion and congestion of the intestine and pyloric caecae. Perivascular inflammation was a common finding in the livers examined. The lesions in the kidney were consistent with haemorrhagic kidney syndrome and were reproduced experimentally. This appears to be the first case report of infectious salmon anaemia in New Brunswick.

Journal of Applied Ichthyology 20 6 525 529 Berlin, Germany: Blackwell Publishing.

A systemic infection of a Rickettsia-like organism (RLO) in cultured sea bass is described for the first time. In hatcheries, clinical signs were lethargy, inappetence and discoloration. Twenty days after transfer to sea cages from hatcheries where the disease existed, fish showed erratic and abnormal swimming behaviour, loss of orientation, and lethargy. Cumulative mortality in colder months of the year reached 30% in hatcheries and 80% in cages. Surviving fish in cages did not show any clinical signs of RLO infection in the subsequent year. Evidence for a systemic distribution of RLO was supported by histolopathological lesions in both infected hatchery and caged fish, where the lesion profile included cranial sensory, central nervous, integumental and alimentary organ systems. Intracranial lesions were primarily characterized by an ascending histiocytic perineuritis and necrotizing congestive meningoencephalitis, with evidence for transfer of infective agents across the blood-brain barrier confirmed by the presence of RLOs within capillary endothelium and histiocytes in inflamed regions of the optic tectum and the cerebellum. In the most severe cases, infection spread to the statoacoustical (semicircular) canal system and the ependymal lining of ventricles, with marked rickettsial-laden histiocytic infiltration of the canal lumen. Integumental lesions were restricted to the oral submucosa, nares and integumental dermis of the cranium. Alimentary lesions were noted in both the liver parenchyma and mucosa/submucosa of the stomach. In all affected organs the RLOs were found by immunohistochemistry to be related to Piscirickettsia salmonis.

Journal of Aquatic Animal Health 11 4 400 405

Infectious salmon anaemia virus (ISAV) was isolated from farmed Atlantic salmon (Salmo salar) associated with an outbreak of haemorrhagic kidney syndrome in the Bay of Fundy, Canada. The virus induced cytopathic effects in salmon head kidney cell line SHK-1 from Atlantic salmon and was positively confirmed as ISAV by an indirect fluorescent antibody test and by reverse transcriptase polymerase chain reaction. Atlantic salmon parr injected with ISAV from the SHK-1 line experienced significant reductions in haematocrits as early as 5 days postinfection (DPI). Mortality began 17 DPI and reached 76% by 24 DPI at a water temperature of 11 degrees C. In a second trial, similarly high mortality occurred in salmon parr injected with 10-fold dilutions of supernatant from ISAV-infected SHK-1 cultures. The ISAV was reisolated from 8 randomly selected salmon that died after experimental infection. Microscopic pathological changes among infected fish included congestion and necrosis, seen in the livers from 7 of 19 samples and in the kidney from 1 of 18 salmon examined. Other tissues affected included gill, intestine, and pyloric caeca. The absence of microscopic lesions in the remaining experimentally infected fish could not be explained.