An overview of furunculosis in Atlantic Canada

Furunculosis occurs in all of the Atlantic Canadian provinces of Newfoundland, Nova Scotia and New Brunswick but not Prince Edward Island. Aeromonas salmonicida has been isolated from both wild and cultured salmonids and non-salmonids. Only "atypical A. salmonicida" (A. salmonicida subsp. achromogenes) has been identified in wild salmonids in Nova Scotia. This subspecies has also been identified in Newfoundland where it has been isolated from Atlantic salmon, Arctic charr and rainbow trout. It is suggested that the number of reports of A. salmonicida in New Brunswick may be an under representation due to the widespread belief that stress-testing has prohibited its transfer to sea cage sites and that active surveillance is not practised. However, there have been few incidence of disease outbreaks attributed to A. salmonicida in New Brunswick marine sites. Disease regulations which attempt to identify the carrier state in hatcheries and then prevent the transfer of positive smolt to seawater may have had some beneficial effects in the past but are now causing the disease to be under-reported since the overall sensitivity of the stress-testing method is likely less than 25% and A. salmonicida prevalence at infected sites may be very low.