The first cases in Scotland were seen in September 2011, says Fish Vet Group vet, Chris Matthews. In Ireland the disease has been recognised since the 1980s, and it is thought that Tasmania has dealt with the disease for over 20 years.
Whilst the discovery of the disease in Scotland has been a particular problem in recent months, Mr Matthews says that seasonal gill disorders (of which AGD is one) can be common in the autumn and early winter, triggered by peak water temperatures at the end of summer.
The AGD agent has been identified in most of Scotland's salmon farming areas, however clinical disease has only developed on individual farms. Fish Vet Group is currently working to identify the risk factors for developing gill problems.
"Gill diseases, including AGD, are always a significant challenge for the industries in Scotland, Ireland and Norway. Because losses due to other infectious diseases are improving due to vaccination and advances in husbandry techniques, the relative importance of losses due to gill disorders like AGD has increased," he says.
Fish Vet Group is working alongside industry fish health professionals to provide advice on the management and treatment of the disease.