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News! Genomic selection for CMS

SalmoBreed have now included QTL CMS as an optional choice of traits in the new product concept SalmoSelect

Cardiomyopathy syndrome or CMS is a serious heart disease in Atlantic salmon caused by piscine myocarditis virus (PMCV). The mortality rates may be moderate, but chronic. The economic losses due to CMS outbreaks can be significant, as the fish are usually affected in later stages of production, mainly in the second year in the sea. In recent years there has also been registered outbreaks on younger fish between 300g to one kilogram. SalmoBreed launches QTL-CMS as a new trait in the Product Program for the 2018/2019 season as a contribution to strengthening the salmon’s resistance to the disease.

Viruses and pathways

CMS has been shown to be associated with piscine myocarditis virus (PMCV). Genetic variation of the virus has been demonstrated in Norway with four main clusters, but the variation is low (1.4% at the nucleotide level), suggesting that all Norwegian isolates belong to a single genotype.

Over the past few years, the rate of CMS eruption has increased throughout the country, but no effective vaccine or treatment is yet available. The virus also occurs in the Faroe Islands, Scotland and Ireland, but not yet in Chile and in Iceland. Horizontal infection has been shown to be the main source of disease spreading.

Challenge tests show strong genetic relationships

After several years of research, SalmoBreed launches increased resistance to CMS in the breeding program. The background for the findings is infection tests conducted at VESO Vikan, where the PMCV virus was directly injected into the fish (i.p model). The fish had the infection for a period of 9 weeks, and upon termination of the test we obtained samples for DNA, PCR and histology. Figure 1. shows large differences in virus levels (Ct values) in the test group from the infection test.

The collected data from the infection test were compared with DNA-samles from the fish in the experiment, and a strong QTL (Quantitative Trait Loci) was detected, which highly affected the virus level in the fish, and the level of cardiovascular damage in fish seen in CMS outbreaks in the field.

Bilde1

Figure 1. The graph shows the distribution of virus levels at the CMS challenge test at VESO Week 2017

Figure 2. is a Manhattan plot showing how the individual genes affect the virus level in CMS infected fish. The blue bar on the right of the chart indicates a specific area of the genome that we call a QTL, and this area has a very strong impact on the trait due to the hight of the bar. This QTL can be used to select fish with higher resistance to CMS virus.

Manhattan Cms

Figure 2. Manhattan plot 

The challenge test showed that fish that had the advantageous version of the QTL had no or very low measurable levels of viruses and little signs of heart injury. In contrast, fish with the unfavorable variant of QTL had a significantly higher viral load and severe cardiac damage (Figure 3).

Virusload

Figure 3. Graph showing the frequency of the fish with different forms of the QTL and the level of virus measured in the fish's heart tissue.

  • 91% of the fish with the homozygous variant QQ had low levels of virus
  • 85% of the fish with the heterozygous variant Qq also had low levels
  • For the homozygous variant qq, only 5% of the fish had low levels of virus
The findings are also supported by direct correlation between the level of virus and mortality recorded in field outbreaks.

SalmoBreed introduces QTL-CMS in the new product concept - SalmoSelect

As of the ova season 2018/2019, SalmoBreed offers increased resilience for CMS in the product concept SalmoSelect.

Only fish with QQ or Qq variants of QTL are included in SalmoBreed’s QTL-CMS product.

The trait is optional and can be added to the product package which includes the traits QTL-IPN, GS-LICE, GS-PD / GS-ISA and GS-SWG (seawater growth) as standard.

Read more about the new product concept here

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