Resistance against IPN

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Updated documentation, per September 2019

 

IPN is considered as one of the most serious infectious viral diseases in most types of intensive aquaculture. Broad geographic coverage and many susceptible species, contribute to a continuous infection pressure from different reservoirs. For such diseases, increased host resistance will be an important contribution in controlling the distribution and extent of the disease.
AquaGen introduced QTL-innOva® IPN to the market in the autumn of 2009. Since then, all AquaGen’s egg products have been delivered with this QTL.Field experience has been very good and the number of IPN outbreaks in salmon in the Norwegian aquaculture industry has been reduced by over 90% from 220 (2009) to 19 (2018).

Figure 1. Total average mortality 90 days after sea transfer of salmon at 44 sites respectively S0 autumn 2010 and S1 spring 2011.

Field documentation with IPNresistant QTL-fish

The first QTL fish that originated from the egg intakes in 2009/2010 were transferred to sea in the autumn of 2010 (S0) and spring 2011 (S1). From these first generations of QTL-innOva® IPN eggs a total of 30.6 million fish at 44 locations were followed up and their performance compared with non QTL fish.
The field documentation showed that both S0 and S1 year class had significantly reduced mortality (Figure 1) and fewer IPN diagnoses (0 and 1 against 1 and 7) than S0 and S1 of non QTL fish to 90 days post seawater transfer.

Efficacy testing with highly virulent IPNV field isolate 

Good challenge models based on a natural waterborne infection are an important prerequisite to both look for potential QTLs and for subsequent evaluation of their efficacy and significance in practice.

Additional use is made of infection trials as a part of AquaGen’s follow up of IPN eggs in the field. Highly virulent IPN virus strains from IPN outbreaks isolated from the field were analysed for genetic modifications (mutations) and are included in challenge tests to determine whether the protective effect of QTL-innOva® is being maintained (Figure 2).

Figure 2. Accumulated mortality in IPN challenge test of salmon fry with different genotypes for IPN resistance. A highly virulent field isolate was used for the challenge. Relative percent survival (RPS) was 86.2% for qQ, and 95.6% QQ compared with qq as a control. Mortality for each group of genotypes is the average of two parallels.

In all, three genotypes were tested, qq (homozygote, IPN sensitive), qQ (heterozygote, IPN resistant) and QQ (homozygote, IPN resistant).
Accumulated mortality to completion of the test was 59.2% for qq, 8.0% for qQ and 2.6% for QQ. That results in a relative percent survival of 86.2 and 95.6% for groups with genotype Qq and QQ. This is in accordance with the expected degree of protection for the commercially available product, QTL-innOva® IPN that has a specified protection level of 82%.

Results from analyses four years after introduction to the market, don’t give any indication that the IPN virus has managed to “figure out” the new defence mechanism contributed by QTL-innOva® IPN.

Products with IPN resistance:

  • AquaGen® Atlantic QTL-innOva® PRIME
  • AquaGen® Atlantic QTL-innOva® SHIELD
  • AquaGen® Atlantic QTL-innOva® GAIN
  • AquaGen® Atlantic QTL-innOva® TERRA-nOva®

Benefits of QTL-innOva IPN:

  • Fish have defence against IPN for the whole of their life
  • Optimised QTL-analysis provides a high degree of assurance that QTL-eggs are composed of high resistant variants, qQ and QQ for IPN
  • Repeated laboratory IPN challenge tests confirm the on-going high level of protection against IPN
  • Field experience has given very positive feedback on performance under commercial conditions