Wild-caught saithe Pollachius virens were experimentally exposed to an isolate of infectious salmon anaemia virus (ISAV) of Norwegian origin. Mortality attributable to ISAV did not occur following exposure by intra-peritoneal (i.p.) injection of virus or by cohabitation with ISAV-infected Atlantic salmon Salmo salar. Despite the individual testing of 120 ISAV-exposed saithe, ISAV was not detectable using RT-PCR, the most sensitive ISAV diagnostic tool demonstrated to date. Furthermore, saithe exposed to ISAV-infected salmon were not capable of transmitting virus when transferred to tanks containing naïve salmon. Thus saithe appear to be resistant to this Norwegian isolate of ISAV and incapable of supporting its replication. Saithe which co-exist with salmon in and around aquaculture facilities are considered unlikely to have a significant impact on the epizootiology of ISAV.
KEY WORDS: Infectious salmon anaemia virus · ISAV · Orthomyxovirus · Saithe · Pollachius virens Resale or republication not permitted without written consent of the publisherDis Aquat Org 50: [13][14][15][16][17][18] 2002 Salvelinus alpinus following intra-peritoneal infection, without the occurrence of clinical ISA disease ). Thus, it is possible that all of these salmonid species could function as a reservoir for ISAV in areas where outbreaks of disease among cultured Atlantic salmon have been reported.An additional candidate as a vector of ISAV is saithe Pollachius virens. Saithe are often found close to fishfarm cages, and young saithe can enter through the mesh of fish-net cages where they may grow rapidly (Bruno & Stone 1990). Thus, if saithe could act as a carrier species for ISAV, they might represent an important vector for the spread of disease between wild and farmed fish. Indeed, saithe have been shown to play a potential role in the spread of sea lice Lepeoptheirus salmonis to Atlantic salmon (Bruno & Stone 1990). Given the fact that L. salmonis have also been implicated in the transmission of ISAV (Nylund et al. 1993), the role of saithe as a potential reservoir for ISAV is an important issue to address. This study was thus designed to investigate the susceptibility of saithe to ISAV and to investigate their potential for transmission of ISAV to Atlantic salmon.
MATERIALS AND METHODSCell culture and virus propagation. The salmon head kidney (SHK-1) cell line was used for the isolation, propagation and identification of virus in this study, according to previously described methods (Dannevig et al. 1995). A Norwegian isolate of ISAV (Glesvaer/2/90) was used for experimental infections.The isolate was kindly provided by the Veterinary Institute, Oslo, Norway (Passage 3 in SHK-1 cells).Fish. Atlantic salmon were obtained from a commercial producer (Follasmolt AS; mean weight 64.1 g). Saithe were wild caught in Norwegian waters with no history of ISAV in that area (mean weight 54 g). Prior to commencing the experimental infection study, 10 fish of each species were individually screened for the presence of ISAV by RT-P...
The objective of our experiments was to study the persistence and dissemination of orally administered Salmonella in smoltified Atlantic salmon. In experiment 1, salmon kept at 15 degrees C were fed for 1 week with feed contaminated with 96 most-probable-number units of Salmonella Agona per 100 g of feed and then starved for 2 weeks. Samples were taken from the gastrointestinal tract and examined for Salmonella 1, 2, 8, 9, 15, and 16 days after the feeding ended. In experiment 2, Salmonella Agona and Montevideo were separately mixed with feed and administered by gastric intubation. Each fish received 1.0 x 10(8), 1.0 x 10(6), or 1.0 x 10(4) CFU. The different groups were kept in parallel at 5 and 15 degrees C and observed for 4 weeks. Every week, three fish in each group were sacrificed, and samples were taken from the skin, the pooled internal organs, the muscle, and the gastrointestinal tract and examined for the presence of Salmonella. The results from the two experiments showed that the persistence of Salmonella in the fish was highly dependent on the dose administered. Salmonella was not recovered from any of the fish that were fed for 1 week with the lowest concentration of Salmonella. In the fish given the highest dose of Salmonella, bacteria persisted for at least 4 weeks in the gastrointestinal tract as well as, to some extent, the internal organs. The present study shows that under practical conditions in Norway, the risk of Salmonella in fish feed being passed on to the consumer of the fish is negligible.
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