Following a request from the European Commission as regards certain crustacean diseases, the Panel on Animal Health and Welfare (AHAW) was asked to deliver a scientific opinion on possible vector species and live stages of susceptible species not transmitting the diseases. The mandate was accepted by the Panel on Animal Health and Welfare on the 1st of February 2007. The mandate included diseases affecting three different groups of aquatic animals: molluscs, crustaceans and fishes. This opinion focuses exclusively on crustacean diseases. The mandate was composed of two questions: i) which species may be responsible for the transmission of a specific disease by acting as vector species for a disease listed in Annex IV Part II to Directive 2006/88/EC, and, in particular, which life stages and under which conditions those species can transmit disease, and, ii) which life stages of the susceptible species listed in column II of the table in Annex IV part II to Directive 2006/88/EC may not transmit the diseases listed in the same annex. Article 17 of the Directive that regulates the introduction of live aquaculture animals of vector species into disease-free areas requires that a list of vector species is drawn up. There is no published scientific evidence for the role of farmed non-susceptible aquatic animals as mechanical vectors in the transmission of Taura Syndrome Virus and Yellow Head Virus. There is published scientific evidence for the role of some farmed non-susceptible aquatic animals as mechanical vectors for White Spot Syndrome Virus. These are Branchiopoda (Artemia sp.), Rotifera and Copepoda. Following a qualitative release and exposure assessment, potential species or groups of species that may act as vectors for the listed pathogens were identified. The likelihood of transfer and establishment of the listed pathogens by the potential vector species or group of species ranked from negligible/extremely low to moderate, under stated conditions. Marine molluscs (if sourced from and introduced to a site where the susceptible species is found) were identified as the most likely vector species for the three pathogenic agents, having a moderate likelihood. Crustaceans and fish species had a lower likelihood. Significant lack of data on prevalence, resistance of the listed pathogens outside the hosts and distribution and infectivity parameters of the diseases/agents contributed to a high degree of uncertainty about the likelihood estimates of transfer and establishment of the hazard. Although the consequences of establishment were assumed to be severe, the actual acceptable level of risk did not form part of the mandate. Concerning the first question of the Terms of Reference, it was concluded that: Taura Syndrome Virus has not been described in eggs, zygotes or larvae. Yellow Head Virus and White Spot Syndrome Virus have been detected in eggs and early larval stages. Furthermore, in respect to eggs: i) there is no scientific evidence to prove the absence of vertical transmission for any of the listed diseases, ii) there is evidence of egg-associated transmission for Yellow Head Virus and White Spot Syndrome Virus. It was recommended that all life stages of the susceptible species should be considered as being able to transmit the listed diseases. During the development of the report a number of issues were identified which were not included in the terms of reference: i) despite the increasing importance of European crustaceans as a resource, very little is known about the health status of the European stocks or their susceptibility to the diseases listed in CD/88/2006/EC, ii) intra community and trade with third countries of live, fresh and frozen crustaceans have been associated with the transfer of crustacean pathogens. Trade of live crustaceans for human consumption is frequent. Crustaceans for human consumption are often kept in insecure (in contact with open waters) holding facilities for variable periods of time, iii) trade of ornamental crustaceans represents a potential risk for disease introduction, and, iv) given the very wide variation in pathogenicity of the many strains of listed crustacean viruses, there is currently great imprecision and lack of uniformity in the definition of listed diseases and their causative agents, which is creating confusion for pathogen characterization, classification, and diagnostic tools. All of these issues require considering for their impact on disease introduction and transmission.
