THREE STEPS TO PROTECT AGAINST INFECTIOUS SALMON ANEMIA
Reykjavik: StofnFiskur systematically work against ISA on three fronts. As of today, the company is the only one in the world with permission from the Chilean authorities to import salmon eggs to Chile.
Benefiting from natures ground heat and water, and expertise built through 25 years of salmon breeding, StofnFiskur can safely claim to be a world leader when it comes to ISA free ova.
Bio secure production
StofnFiskur keep their brood fish and produce eggs in closed, land-based units. Water, both sea and fresh water, comes from underground sources that do not contain salmon pathogens. Strict quality control with frequent sampling and analysis ensures that the water is in accordance with regulatory requirements and the company’s own standards.
It is shown that the ISA virus can infect vertically (Marshall et al. 2014), so keeping the entire system free of ISAV is crucial both for the broodfish in production and for customers receiving ova StofnFiskur production is audited by Sernapesca in Chile and OIE, the World Organisation for Animal Health. StofnFiskur is the only company in the world authorised to send salmon ova into Chile. ISA has been especially aggressive in Chile, and Chilean authorities take strict measures to prevent new outbreaks. Among the requirements StofnFiskur meet in order to send eggs to Chile, production sites and fish must be documented free of the virulent form of ISAV; ISAV HPR-deleted.
Since 2009 StofnFiskur routinely screen fish by PCR to ensure and document that the fish do not carry the ISA virus. Before 2009, a large number of tests in cell lines (CHSE-214) where performed annually. In 2016, samples from close to 13,000 fish were analysed by PCR. None of the samples were positive for virulent ISA.
Screening for HPR0
HPR0 is a non-virulent variant of ISA virus. This means that although fish carry the HPR0 variant, it is not suffering a clinical ISA outbreak. Over the years researchers have discussed whether HPR0 variants may evolve to become virulent and therefore pathogenic. Christensen et al. (2011) reported that despite the detection of the HPR0 variant of the virus in 8.1% of the fish that were screened in the Faroe Islands, no virulent virus was found. The authors concluded that there was little danger that a bystander HPRO variant would be the source of outbreaks of clinical ISA.
StofnFiskur has nevertheless chosen to screen fish used for breeding for HPR0; tissue from both heart, gills and kidneys are analysed.
This monitoring has been conducted since 2009. The results show that the proportion of fish where HPR0 was found has been reduced from 1.8 % in 2009 to 0.3 % in 2016 (Figure 1). This has been a precautionary measure; stricter than government orders in some of the countries to which the company exports ova.
Figure 1 shows how screening and exclusion has led to reduced frequency of fish with HPR0 generation to generation; fish screened in 2009 is parent fish to 2013 fish, 2010 to 2104 etc.
At the Frisk Fisk Conference in Bergen, Norway, in February 2017, Christensen et al (2017) presented new findings. There are now indications that HPR0 can change into a virus variant that provides a mild clinical outbreak. StofnFiskur´s decision to screen HPRO out of broodstock population proves thus to be wise, and the work is continuing with the goal of having a population free from HPR0.
Selection of strong individuals with natural resistance against ISAV
ISAV is one of the viruses for which StofnFiskur is performing challenge trials. Improvement of resistance to ISA has been part of the StofnFiskur breeding program since 2014, and the Norwegian sister company, SalmoBreed, has worked continuously with ISAV since 2001. The breeding programmes includes family selection and genomic selection, with the aim to deliver ova with increased resistance against ISA.
All sampling and PCR assays for StofnFiskur are done in cooperation with the Icelandic FSA. Results presented here are in cooperation with veterinarian, Gisli Jonsson.
Christensen, D., MacBeath, A., Aamelfot, M, Matejusova, I. Four Rier, M., White, P., Petersen, P. and Falk, K. (2017) Transition of ISAV_HPR0 two ISAV-HPR-deleted Abstract Frisk Fisk conference Page 24
Christensen, D., Østergård, P., Snow, M., Dale O. and Falk, K. (2011) A low-pathogenic variant of infectious salmon anemia virus (ISAV-HPR0) is highly prevalent and Causes a non- clinical transient infection in Farmed Atlantic salmon (Salmo salar L.) in the Faroe Islands Journal of general virology, 92, 909-918
Marshall, S., Ramires, R., Labra, A., Carmona, M. and Munos, C. (2014) Bona Fide Evidence for natural vertical transmission of Infectious Salmon Anemia Virus in freshwater brood stocks of Farmed Atlantic Salmon (Salmo salar ) in Southern Chile. Journal of Virology 88 (11) 6012-6018
Personal communication and analytical results
Jonsson, Gisli, Veterinary Officer for Fish Diseases, Matvælastofnun / Icelandic Food and Veterinary Authority