PD test to be available “within 2-3 years”

The test, which was developed by researchers at the University of Glasgow, in cooperation with Biomar and Marine Harvest Scotland, suggests that a simple measurement procedure could be used to detect Atlantic salmon infected with salmonid alpha virus, which causes pancreas disease (PD).

Called a selective precipitation reaction (SPR), the team has filed for a patent for the test, which could potentially be developed into a rapid analysis system, allowing the disease to be diagnosed much earlier than is currently possible.

Professor David Eckersall, Professor of Veterinary Biochemistry and leader of the research team at Glasgow’s Institute of Biodiversity, Animal Health and Comparative Medicine, explains details of the breakthrough to Fish Farming Expert.

What is the timeframe for creating a rapid analysis system using your test and how much could this shorten the diagnosis process by?

A rapid analysis system based on our results should be achievable within an estimated 2-3 years, provided there is sufficient investment, as the basic reagents required are readily available and it is a simple method. A major requirement is for validation in the field so that the exact benefit and value of applications of the test can be established. My understanding is that it could shorten the diagnosis by several days, as currently samples have to be sent to a central laboratory for analysis that is relatively time-consuming.

What’s the likelihood of being able to apply the SPR test to other diseases and are there any in particular that it might be suited to detecting?

There is a real likelihood that the SPR test may have applications in other diseases and other fish species, as the test measures a pathophysiological response of tissue such as muscle, pancreas and heart to the viral infection. It is possible that diseases such as infectious pancreatic necrosis (IPN) and heart and inflammatory muscle inflammation (HSMI) of salmon would give results reflecting tissue damage while modifications of the test may be able to provide differential diagnosis. Thus the SPR is not just a test for PD alone, rather that PD was used as a model for viral myopathies (muscle damage). It will be important in PD management but also as a general health test. However, considerable further research is needed to examine this in detail.

How widespread a problem is PD (both in Scotland and further afield)?

It is known that PD sporadically occurs in all areas in which salmon are farmed in Scotland and Ireland. Over the years, knowledge of the disease has improved and PD management practices are robust, so clinical outbreaks are rare. Geographically distinct subtypes of the SAV virus are found. A commercial vaccine is available which all producers use. Norway is similar although it’s a notifiable disease with different subtypes and the management practices are different. SAV is not found in Canada or Chile. However, as mentioned above, the SPR Test would be suited to routine proactive health monitoring as a general health test and not just for PD diagnosis.

How revolutionary are your discoveries compared to other work that’s currently being done in the PD diagnosis field?

The revolutionary aspect of our results is the discovery that there is such a marked change in the blood (serum) of salmon with PD that their serum contains a level of largely muscle-derived protein that can lead to the SPR reaction. Once we discovered this pathophysiological response to the disease we used technology to monitor and measure the SPR that has been available in a biochemistry laboratory for decades. The difference to most health monitoring diagnostics is that these are normally based on pathogen detection and identification, but there are few reliable and sensitive tools for identifying clinical disease without non-destructive investigation, thus the SPR would be suited to routine proactive health monitoring. The issue being that many pathogens are ubiquitous and disease management strategies cannot be put in to action each time they are identified. The closest to current PD diagnosis is to the measurement of creatine kinase (CK) in serum which is also derived from the salmon’s muscle. Tests for CK are available but have a problem in that high levels of CK are found even in healthy salmon so a result may be difficult to interpret.

What was serendipitous about the discovery?

Our laboratory is a global centre in development and assessment of diagnostic tests for use in animal health studies. In collaboration with partners in aquaculture, we were investigating the use of a number of tests developed for animals such as cattle, pigs and dogs for use in the detection of PD in Atlantic salmon. While assessing the use of a biomarker called ceruloplasmin, used as a test for an acute phase response to infection in mammals, we obtained very high results with serum from salmon with PD. After repeating the study and examining the result in detail we concluded that the levels of ceruloplasmin indicated by the test were biologically impossible. Close inspection of the test procedure identified that these apparently very high results were not due to ceruloplasmin at all, but were caused by some interfering factor in the test which we were able to identify as a protein-based precipitate that only occurred with samples from the salmon with PD but not from healthy fish. This observation was the basis on which the SPR test has been built. A good example of serendipity in science where a strange initial observation has led to a valuable discovery.