Viral haemorrhagic septicaemia virus, infectious haematopoietic necrosis virus and HPR-deleted infectious salmon anaemia virus – Risk of introduction in free areas through fertilised eggs and gametes
New research assesses the potential for introducing several viruses – viral haemorrhagic septicaemia virus (VHSV), infectious haematopoietic necrosis virus (IHNV), and highly polymorphic region-deleted infectious salmon anaemia virus (HPR-deleted ISAV) – into areas currently free of these diseases. The assessment focused on the risks associated with the movement of fertilised eggs and gametes, essential components of aquaculture and fish farming.
Understanding the Risks
The European Food Safety Authority (EFSA) Panel on Animal Health and Welfare (AHAW), comprised of experts including Søren Saxmose Nielsen, Julio Alvarez, and Anette Boklund, among others, conducted the study. While the research found no evidence of these viruses being directly passed from parent fish to their eggs, the possibility of surface contamination remains a concern. This means the viruses could be present on the eggs or gametes, rather than within them.
Mitigation Strategies and Probability
The study evaluated the effectiveness of various preventative measures, particularly those outlined in a new draft chapter – 4.Z – of the Aquatic Animal Health Code developed by the World Organisation for Animal Health. If these recommendations are fully followed, including individual testing of broodfish, the median probability of introducing VHSV or IHNV through imported fertilised eggs is estimated at 0.36%. For HPR-deleted ISAV, the probability is 0.4%.
However, the risk can be significantly reduced through disinfection. Two rounds of disinfection – once when the eggs are “green” and again when they are “eyed” – lowered the probabilities to 0.02% and 0.01% respectively. Further disinfection upon arrival at the importing facility could reduce the risk to virtually zero when combined with two disinfections at the origin.
For gametes, the risk assessment indicated a probability of introduction ranging from 0% to 0.3% when individual testing of broodfish is combined with the other recommended measures.
What Could Happen Next
If the recommendations in the draft 4.Z chapter are widely adopted, it is likely to lead to more standardized and rigorous testing and disinfection procedures for fertilised eggs and gametes traded internationally. This could, in turn, lead to increased confidence in the safety of these products and potentially facilitate trade. However, the effectiveness of these measures depends on consistent implementation across all exporting and importing regions. A lack of compliance could leave areas vulnerable to outbreaks. Further research could focus on optimizing disinfection protocols and exploring new methods for detecting viral contamination.
Frequently Asked Questions
What viruses were assessed in this study?
The study assessed the risk of introducing viral haemorrhagic septicaemia virus (VHSV), infectious haematopoietic necrosis virus (IHNV), and highly polymorphic region-deleted infectious salmon anaemia virus (HPR-deleted ISAV).
Can these viruses be passed directly from parent fish to their eggs?
No evidence of true vertical transmission of these viruses was found, meaning the viruses are not directly passed from parent fish to their eggs.
What is the most effective way to reduce the risk of introducing these viruses?
Two disinfections of fertilised eggs at the origin, potentially combined with a further disinfection upon arrival at the importing facility, is the most effective way to reduce the risk to virtually zero.
How might these findings impact the future of aquaculture and fish farming?