ABSTRACT. A matched case-control study of infectious salmon anaemia (ISA) risk factors in Norwegian salmonid sea sites was performed in 1993. The distribution of potential exposure factors associated with the site management and location was compared in 2 paired groups of sea sites, one group comprising 37 ISA-positive sites and the other 37 1SA-negative sites. The risk of ISA was found to be significantly associated with the location of the site. Location within 5 km from a salmonid slaughterhouse gave an ISA odds ratio of 13.0 compared to location further away. The risk of infection increased by 8.0 if the site was situated closer than 5 km to another ISA-positive site as compared to the risk when the site was more than 5 km away. Disinfecting the waste water from the slaughtering and processing plants seemed to prevent transmission of ISA. The density of fish markets for sea-caught fish was higher in the vicinity of cases than of controls. The risk of ISA was associated with the number of hatcheries delivering smolt to the sea sites, and the risk increased if the hatcheries were located outside the site's home county. The overall results from the present study indlcate that 1SA is mainly transmitted from infected salmonid sources to clean sites through sea water Further disease control measures should concentrate on minimising the risk of transmission through sea water by shortening the time period between the diagnosis of ISA and the elimination of posltive sites, and should work towards the establishment of 5 km as a minimum distance between sea sites In addition, decontamination systenls must be systematically introduced into the fish processing industry. The implementation of good sanitary practices by fish farmers may also reduce the nsk of ISA.KEY WORDS: Epidemiology Disease -Risk factors . Infectious salmon anaemia INTRODUCTIONThe first case of infectious salmon anaemia (ISA) was diagnosed in Atlantic salmon parr Salmo salar L. in a hatchery on the west coast of Norway in 1984(Thorud 1991. In this outbreak, which lasted for several months, fish mortality in the hatchery reached approximately 80%. The affected parr were kept in smolt tanks where the fresh water was mixed with raw sea water, but afterwards no naturally occurring cases were registered in fry or smolt prior to seawater transfer until 1995. The most serious problems associated with the diagnosis of ISA in the farmed population of Atlantic salmon were registered in sea farms. The mortality associated with ISA in sea farms varies considerably from insignificant to moderate.In 1995 the causal virus of ISA was isolated from cultured cells in the laboratory (Dannevig et al. 1995). Prior to this confirmation of the viral aetiology, the results from several studies indicated that the disease was transmissible (Thorud 1991, Dannevig et al. 1994, Vagsholm et al. 1994). The virus is not yet fully classified, although it seems to be an orthomyxo-like RNAvirus (S. Mjaaland pers, comm.).Since the first appearance of ISA in 1984, the disease has been co...

An epidemiological longitudinal study comprised information obtained from 124 randomly selected Norwegian sea-sites housing post-molts of Atlantic salmon, Salmo salar L. Information on crude cumulative mortality, fish characteristics and farm factors was gathered by the veterinary practitioners servicing the farms. The observation period lasted from the time of sea transfer of the smolts in the spring until 1 October 1991. On average, 116480 smolts were transferred to each sea-site. The mean crude cumulative mortality of postsmolts during the period concerned was 16 8%. The cumulative farm-level incidence was 540% for furunculosis, 39 5% for infectious pancreatic necrosis (IPN) and 10 5% for vibriosis. Occurrence of any of these specific infectious diseases in the post-smolt was significantly associated with mortality. The risk of furunculosis was significantly related to the location of the sea site. Mixing of smolt from many freshwater hatcheries in the sea farm increased the risk of IPN significantly. In addition, the risk of IPN was related to age of site and geographic location. The mean cumulative mortality in 1-year-old smolt groups was 17 5%, significantly greater than in two-year-old fish (7 9%). In addition, the method used to transport fish from the freshwater hatchery to the sea site was significantly associated with mortality. Neither the weight of smolts at sea transfer nor the date of transfer were significantly related to mortality.

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Aim: To investigate the bacteriological quality, and the occurrence of selected pathogenic bacteria from organically grown Iceberg lettuce fertilized with bovine manure in the form of compost, firm manure and slurry in a 2-year field trial. Methods and Results: Samples of soil, fertilizer, fertilized soil, seedlings and lettuce were analysed for aerobic plate counts (APC), thermotolerant coliform bacteria (TCB), Escherichia coli, E. coli O157:H7, Salmonella spp. and Listeria monocytogenes. No difference in bacteriological quality could be shown in lettuce at harvest, however, APC varied significantly from year to year in the study. The various treatments gave significantly different APC and numbers of TCB isolated from fertilized soil. Escherichia coli O157:H7 was isolated from firm manure and slurry, and soils fertilized with the respective fertilizers the second year, but were not recovered from the lettuce. Conclusions: No difference in bacteriological quality could be detected in lettuce at harvest after application of various types of manure-based fertilizers grown under Norwegian conditions. Significance and Impact of the Study: The results may indicate that the use of manure does not have considerable influence on the bacteriological quality of organic lettuce. However, others have suggested that there is a risk by using manure. There is a need for more research in the field.