Bespoke vaccines

Stirling team targets AGD with novel control strategy

Amoebic Gill Disease (AGD) is rapidly emerging as a major threat to the Atlantic salmon aquaculture industry. It is caused by the amoeba Paramoeba perurans, which floats freely in seawater, only becoming a problem when it attaches to the gills of a fish it encounters.

Infection leads to the characteristic appearance of white spots and streaks on the gills and, as the disease worsens, fish become lethargic and show signs of respiratory problems which can ultimately lead to death if left untreated.

The severity of outbreaks of AGD are seen to increase in the summer months, when the sea temperatures rise and the parasite multiplies very quickly.

This disease was originally reported in Tasmania in the mid-1980s but since then has spread to become a global problem - outbreaks have been reported from New Zealand, the United States, Canada and Chile to France, Spain, Ireland, Norway and Scotland.

It does not just infect salmonid species but also non-related fish species such as sea bass, turbot and - worryingly - cleaner fish, including ballan wrasse and lumpfish, which are stocked alongside salmon in sea cages as part of a biological lice control programme.

Currently, treatments are restricted to bathing infected fish in hydrogen peroxide or freshwater – both methods are costly and logistically challenging and, in addition, can have detrimental impacts on the health and welfare of already compromised sick fish. This disease is currently costing the global salmon farming industry millions of pounds a year in treatments and fish losses.

An ongoing project funded by Innovate UK brings together fish health and vaccinology expertise from the University of Stirling’s Institute of Aquaculture, Ridgeway Biologicals

- the UK’s primary manufacturer of autogenous vaccines, and Marine Harvest.

The aim of the project is to develop and test a novel control strategy against AGD in farmed salmon stocks, through the use of autogenous vaccines – that is, farm-specific vaccines or those that are individually tailored for each farm experiencing an outbreak of AGD.

Such vaccines can be produced under specific regulations, controlled by the Veterinary Medicines Directorate, and offer the potential to be produced and deployed rapidly in the face of emerging AGD threat.

It was only in 2008 that the amoeba responsible for the disease was positively identified as Paramoeba perurans and, since then, dedicated research has resulted in the ability to culture this organism in a laboratory setting.

The Institute’s Dr Sophie Fridman has visited a number of Marine Harvest sites on Scotland’s west coast and collected amoebae from the gills of salmon infected with AGD and grown them up in the lab at Stirling.

The consortium is now culturing, isolating, characterising and comparing these different amoebae strains and developing vaccines based on the results.

The vaccines will then be tested in experimental trials in the laboratory environment. Experimental vaccines that prove effective in the laboratory will be used to vaccinate fish in sea cages to assess vaccine efficacy in fish following natural exposure to amoeba.

The benefits of this research are far reaching. Not only will it provide valuable information to the fish disease research community, it will also directly benefit the global salmon aquaculture industry through reduction in AGD and improved productivity and sustainability of production.

They offer the potential to be produced and deployed rapidly”