Scallop introductions and transfers, from an animal health point of view

The effects of transfers and introductions of bivalue molluscs are always more or less unpredictable. Moving scallops, there is a risk of introducing pathogenic agents or of disturbing the balance between potentially pathogenic agents and host species in the recipient ecosystem. Risk is not eliminated by merely following official regulations. Some factors which may be important in order to assess risk, and to choose the level of risk we are willing to accept, are: The existence of "stowaways'', and the action of mechanical vectors. One organism may carry another, and it is seems impossible to obtain a "clean'' organism, in spite of long quarantines. The biological vector function. There may be unknown reservoirs, intermediate or alternative hosts of pathogenic agents in the "new'' environment. An introduced species may also carry potentially pathogenic agents into a new ecosystem. The often lacking knowledge concerning epizootiology. Life cycles of many pathogenic agents are poorly known, as are the infectious dose of agent, influence of environmental factors on disease, etc. The diagnostic tools, and the "human factor'' in diagnostics. Methods are often not sensitive enough to detect a pathogenic agent in a carrier state, or immediately after the agent has entered the host, or at a low prevalence/how intensity level. It is also important that personnel are sufficiently trained to do the diagnostic work. The official priority of disease control. There are no notifiable diseases of scallops. EC regulations, and the "one area/one agent/one bivalve species'' management. National and international trade, including illegal transport of live bivalves. Considering these factors enables a better focus on the risk factors and the assessment of risks associated with introductions and transfers of scallops. Consideration may also help to clarify the scientific level of knowledge and experience required to handle scallop diseases, and focus on practical problems in scallop health control.