Acronym NA
Category
Aquaculture
Title Studies of factors related to susceptibility or resistance in IPN virus infection in Atlantic salmon throughout the production cycle Programme National Programme
Instrument (FP6)
Contact Type (FP7)
Strand (Interreg)
NA
Theme (FP7)
Activity Area (FP6)
Regional Area (Interreg)
Action (COST)
NA
Specific Programme (FP7)
NA
Funding source National Coordinator Øystein Evensen Coordinator email oystein.evensen@veths.no
Coordinator institution
NMBU - Norwegian University of Life Sciences (Norway)
Institutions involved
NA
Start year 2002 End year 2005 Funding (€) € NA Website https://www.fhf.no/prosjekter/prosjektbasen/552102/ Summary "This project will aim at characterizing in detail isolates of IPNV from two different categories of freshwater and seawater operations. The fish will be followed all the way from the broodstocks through to harvest. The categories chosen have either a record of chronic IPN problems (throughout the cycle) and one category with few problems reported. Through collaboration with Marine Harvest Norway, the project will have access to the different categories as described. Isolates of IPN virus will be subject to serotyping and sequencing for detailed characterization at the genomic level and subsequent challenge studies in fry. Selected isolates with high and low virulence will also be tested in challenge experiments using par/smolt stages.
Results
• The prevalence of subclinical and clinical IPN virus infections has been defined. Subclinical infections have a low IPNV infectivity in fry or parr while clinical IPN is associated with high virus prevalence. In smolts, the infectivity of isolates causing subclinical infections can be very high but without causing clinical symptoms.
• The presence of virus isolates in fish at fresh water stage and yet absent at sea water stage suggests lack of persistence in some virulent isolates. It must be noted however that sampling in this study was purposive during outbreaks to maximise the chances of isolating the virus. Because of this, virus infectivity in fish populations must be interpreted with caution.
• The similarities between sequences of fresh and sea water isolates of related fish groups suggest that sea water outbreaks are a recurrence of freshwater infections. Each hatchery seems to have an “in-house” strain. The fish pick up the virus during the freshwater stage and are transferred to sea with it probably through persistent infections.
• Infection with IPNV during the fresh water stage does not necessarily lead to resistance against the disease in the sea water as outbreaks may re-occur.
• Introduction of fish groups from more than one fresh water site encourages intermixing of different virus isolates and is a recipe for disease outbreaks. However, it is also interesting to note that isolates with PTAY motifs (Glomfjord isolate) seem to confer protection against virulent isolates. This finding requires further investigation.
• The contribution of vertical transmission towards the perpetuation of IPNV in the production cycles examined in this study is of limited importance since no virus was isolated from the brood stock, eggs or milt. Our findings however suggest that hatcheries on the other hand are an important source of infection. Nevertheless, brood stock testing is still recommended as a means of keeping vertical transmission of the virus in check.
• Finally, the differences in mortalities of fish from the same group when transferred to different sea water sites suggests that the environment plays a role in the epidemiology of IPN. Factors such as pH, superoxygenation etc. are well known to play a role in predisposing fish to IPN disease outbreaks and must be studied in more detail."
Keywords
Disease;
Genomic sequencing;
Fish;
Salmon;
Marine Region
41
Norwegian Sea (27.IIa)
13
Northern North Sea (27.IVa)
2
Marine Region Map
