WWW.WAS.ORG • WORLD AQUACULTURE • DECEMBER 2012 37 (CONTINUED ON PAGE 36) disinfection methods or recirculated, to untreated seawater representing the greatest risk. Risks of vectors increase from personnel who are not in contact with water or fish material, or work in only one location, to those who get in contact with the water, to thos who work directly with fish. Different types of boats have different risks, extending from delivery boats to service boats to well boats, which represent the greatest risk. The matrix can also be adapted to sum up biosecurity risks of introducing a specific infection. Figure 2 illustrates the sources of infection considered to be most important for infectious pancreas necrosis virus, a virus causing disease outbreaks both in freshwater and seawater and having the potential of vertical transmission through the egg (Munroe 2010). Farmed salmon in seawater, as well as smolt and anadromous wild salmonids (Johansen et al. 2011), are considered to be the most important reservoirs of IPN. As a consequence, seawater and freshwater where salmonids are migrating constitute high risk, together with well boats and net cleaners. For pancreas disease virus (Figure 3), horizontal transmission in seawater is the most important route for spread of disease (Jansen et al. 2010). Salmon in sea-farms, together with seawater, well boats and net cleaners are considered to have the highest risk level, while water supply, being the habitat of potentially infected fish, comes next, together with smolt and vectors with potential close fish contact. Infectious salmon anaemia virus exists as a low virulent variant, called HPR0, and virulent variants, probably being the result of spontaneous mutations in farmed salmon (Christiansen et al. 2011). The low virulent variant is widespread and wild salmonids, together with farmed, are thought to be the reservoir (Figure 4). The virus may then be spread with seawater. When virulent variants arise, the infection may spread horizontally in seawater and with infected fish, then including well boats as a risk factor (Figure 5). Conclusion When a biosecurity plan is developed for a particular farm, the possible sources of infection must be evaluated, together with information on the epidemiological situation and disease panorama in the region. Based on such knowledge, control points and biosecurity measures have to be determined. A smolt farm on land can more or less be isolated in a biosecurity sense, in the same way as a production unit for farm animals. However, a sea-site is continuously exposed to the surrounding waters and biosecurity measures should include a larger zone than only one farm. Notes 1 Norwegian Veterinary Institute, PO Box 750 Sentrum, N-0106 Oslo, Norway atle.lillehaug@vetinst.no * Corresponding author 2 Aqua Gen AS, PO Box 1240 Sluppen, N-7462 Trondheim, Norway 3 Havbrukstjenesten, Siholmen, N-7260 Sistranda, Norway References Aldrin, M., B. Storvik, A. Frigessi, H.Viljugrein and P.A. Jansen. 2010. A stochastic model for the assessment of the transmission pathways of heart and skeleton muscle inflammation, pancreas disease and infectious salmon anaemia in marine fish farms in Norway. Preventive Veterinary Medicine 93:51-61. Christiansen, D.H., P.S. Østergaard, M. Snow, O.B. Dale and K. Falk. 2011. A low-pathogenic variant of infectious salmon anemia virus (ISAV-HPR0) is highly prevalent and causes a non-clinical transient infection in farmed Atlantic salmon (Salmo salar L.) in the Faroe Islands. Journal of General Virology 92: 909-918. Council Directive 2006/88/EC of 24 October 2006 on animal health requirements of aquaculture animals and products thereof, and on the prevention and control of certain diseases FIGURE 4. Level of risks for the introduction of low virulent infectious salmon anaemia virus (HPR0) into an Atlantic salmon production site. Lowest risk is to the left (green), increasing towards the right (red). FIGURE 5. Level of risks for the introduction of virulent infectious salmon anaemia virus into an Atlantic salmon production site. Lowest risk is to the left (green), increasing towards the right (red).
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