Qualitative risk assessment of introduction of anisakid larvae in Atlantic salmon (Salmo salar) farms and commercialization of products infected with viable nematodes

In this study, the likelihood of introduction of anisakid larvae in Atlantic salmon (Salmo salar) farms and subsequent commercialization of fish infected by at least one vital parasite was formally assessed using an adaptation of the risk assessment framework for importation of animals and animal products of the World Organization for Animal Health (OIE). The different plausible pathways were identified and outlined. The most recent information concerning the parasite, its definitive, intermediate hosts and the farming practices typical of Atlantic salmon farms were reviewed and used to assess the likelihoods of each key step along the pathways. A matrix for the conditional probabilities was adopted to combine the qualitative estimations and obtain an objective and transparent overall risk of introduction along each route. In order to avoid misinterpretation and overconfidence on the outcome, the uncertainties surrounding the estimations were considered. The only situation for which the assessed risk in a typical Atlantic salmon farm was deemed to be non-negligible involved the ingestion of infected hosts that penetrate the harvesting cages. In this event, the overall risk was estimated as 'Very Low' with a high degree of uncertainty because of the scarcity of information in some of the key steps along the pathway. However, the scientific evidence in support of the overall estimation suggests that the availability of additional data would be unlikely to increase the final estimated risk. On the basis of the available information of the system, the estimated risk of introduction and commercialization of farmed Atlantic salmons infected by viable nematodes resulted 'Very Low' even under a conservative approach. The proposed qualitative model is an objective and transparent method to assess the risk when data and information are scarce and provides a framework for the qualitative assessment of the introduction of alive parasites in aquaculture/mariculture implants and subsequent commercialization of infested fishery products. The framework could be easily adapted to other parasite-host interactions besides anisakid nematodes in Farmed Atlantic salmons.