Animal Health and Welfare
Scientific Opinion on factors relevant for listing diseases of aquatic animals
Report no: 2015: 19
The Norwegian Food Safety Authority (NFSA) has requested the Norwegian Scientific Committee of Food Safety (VKM) to assess which factors should be considered to determine whether an infectious disease should be included on List 3.
There is often a long time delay from when an emerging or new infectious disease of aquatic animals is first identified to when the Norwegian Food Safety Authority (NFSA) has completed their evaluation regarding whether national listing (List 3) should be recommended. Listing is important because it enables interventions to be used in the field. The time lag associated with listing of diseases is mainly due to a lack of knowledge on the disease-causing agent and its epidemiology. Furthermore, some diseases remain listed, but no intervention measures are applied.
In the opinion of the NFSA, the process of diseases being added to the List could be shortened. However, this requires the establishment of efficient routines for inclusion of emerging or new infectious diseases of aquatic animals on List 3 and exclusion of already listed diseases. In this context, “aquatic animals” includes only fish, molluscs, and crustaceans.
The NFSA requested the Norwegian Scientific Committee of Food Safety (VKM) to assess which factors should be considered to determine whether an infectious disease should be included on List 3. This list appears as Annex I in Regulation 17 June 2008 on the placing on the market of aquaculture animals and products thereof, and on the prevention and control of certain diseases in aquatic animals (omsetnings- og sykdomsforskriften for akvatiske dyr). In addition, the NFSA requested VKM to assess which factors of a disease and an infectious agent are significant regarding the effect of subsequent interventions. Nine detailed Terms of Reference (ToR) in the request from the NFSA were addressed by VKM.
The report from the VKM has been prepared by a working group consisting of five members of the VKM Panel on Animal Health and Welfare. The final Opinion was assessed and approved by all members of this panel.
The VKM highlights the following principal factors that should be evaluated when considering whether a disease should be included on List 3:
- the infectious nature of the disease and the efficiency of transmission of the associated pathogen
- the consequences of the disease for farmed aquatic animals and/or wild aquatic animal populations
- the possibilities for disease control
Knowledge regarding the infectious nature of the disease is particularly challenging for new and emerging diseases. In order to meet this challenge, field observations to assess infectivity or contagiousness are valuable, especially before experimental trials are able to provide conclusive results. In the long-term, prevention would have a more positive impact than treatment, as the latter is mainly associated with damage control.
Transmission efficiency is influenced by many factors, including, but not limited to: the course of the disease, the persistence of the infection in the host animals, the range and proximity of susceptible species, the existence and proximity of reservoirs, the environmental stability of the infectious agent, the management and other characteristics of the affected aquaculture facilities, and interactions between farmed aquatic animals and wild populations.
The relevant consequences of the disease to consider are increased mortality, reduced welfare and production losses in farmed populations, and reduced welfare and other impacts on wild populations.
The possibilities for disease control will depend upon the success of hygiene and sanitation measures, and of vaccination. Vaccination would, however, not be applicable in either molluscs or crustaceans.