Unofficial workshop on Red Mark Syndrome at the EAFP
June 1, 2010 at 08:01 PM Unofficial workshop on Red Mark Syndrome at the EAFP
Matthijs Metselaar, Institute of Aquaculture, University of Stirling, Stirling FK9 4LA, United Kingdom.
Red Mark Syndrome (RMS) is referred to by rainbow trout farmers as the biggest problem to their industry, and scientist are far from solving it. Because of a full (and excellent) EAFP program, there was unfortunately no room for an official workshop on RMS, but a room was kindly made available for an unofficial meeting on the topic during the conference. This workshop was organized and chaired by Dr. Matthijs Metselaar, a first year PhD student at the Institute of Aquaculture in Stirling currently working on RMS, in collaboration with Dr. David Verner-Jeffreys, already known for his work on RMS and who organised the last RMS workshop at the EAFP in 2007. The aim of the workshop in Prague was to enable participants to share experiences, and to give people working on RMS new ideas and renewed energy to help answer some of the questions about RMS, so desperately needed by the industry. Over 25 people were present at the meeting.
The Chairman started the workshop with a presentation prepared by Dr. Birgit Oidtmann describing her work on RMS at Cefas. Unfortunately she was unable to attend the workshop to present her work in person. A survey examining outbreaks of RMS was conducted in the winter of 06/07, in which 239 sites were visited in England and Wales. With more than one disease of unknown aetiology having similar signs, a clear case definition was needed. The few publications on RMS clearly explain the need for this. For example distinction between Warm Water Strawberry Disease (WWSD) and RMS had to be made. The 2 major factors which distinguished between them were temperature and treatment, as WWSD is only seen in water above 160C and RMS only below this temperature, and WWSD responds to vitamin C added to feed, while RMS only responds to antibiotic treatment. Dr Patricia Noguera from Marine Scotland added that she did a comparison of pathology of different skin diseases and only included the ones that did not have involvement of the epidermis in the inflammation. All agreed that the case definition given by Dr. Oidtmann was useable and accurate. Data was collected on all trout farms using this clear definition.
Dr Alain Le Breton asked if the condition was also seen in Sea bream by anyone. Some people said that they had seen similar signs in Sea bream and trout species. According to the case definition provided by Dr. Oidtmann it was decided that the disease seen in Sea bream was not covered by the case definition for RMS. So far it is only rainbow trout that appears to be affected by RMS.
The second presentation was on the histopathology of RMS by Dr. Steve Feist in which lesions resulting from RMS were discussed. Scale loss, with inflammation and oedema around this region were regularly seen.
Dr Heike Schmidt from the centre for fish and wildlife health in Bern Switzerland was asked to present the situation in Switzerland. Only 4 cases have been reported in this country so far, and no fish have been imported into the country from UK. Affected fish were all larger than 100 g and the disease was seen between 4-14˚C. Treatment was successful with antibiotics. A case, with what looked like an early lesion, was presented by Dr. Schmidt. Dr. Feist had seen it before but did not think it was related to RMS. Macroscopically, it looked a lot like RMS, but histologically it did not resemble RMS. One case of RMS was also reported from Austria, however the source of the fish was unknown. Other species on the farm, including bach and brown trout both appeared unaffected. A new case of RMS was also reported in brown trout, but results were still preliminary. Serbia reported an outbreak of the disease in rainbow trout and presented this as a poster (P-210) at the conference.
At the end of the presentations, there was time for general discussion, the main focus of which was the aetiological agent of RMS. Points were made as to why suspected agents were plausible or not. Flavobacterium psychrophilum was isolated by Prof. Hugh Ferguson and Dr. Margaret Crumlish at Institute of Aquaculture, Stirling, United Kingdom, but was not seen in America or by other groups working on RMS in the UK. In case of the Swiss outbreaks, F. psychrophilum has been recorded, but these farms were also positive for Rainbow Trout Fry Syndrome. An RLO in full has not yet been isolated and is has not been seen in histological sections of infected tissue. Prof. Brian Austin commentated that this might be due to only naked DNA of the agent being picked up in the methods used, as the fish immune system may have already destroyed the agent at an early stage.
Another point brought up was the reaction seen in the fish during the disease. A few people have already mentioned that it may be a hypersensitivity reaction and Dr P. Noguera emphasized this, with many people agreeing. A big piece of the puzzle is to understand how and why the fish react as they do. Both early lesions and the healing process can help unravel the puzzle according to Dr. Feist. Dr. Una McCarthy added that knowing the type of cells in the reactions can help as well but this is difficult as we do not have the appropriate markers. She looked at the paper on strawberry disease in the US and concluded that the severity of the lesion correlated with the amount of RLO DNA found in these fish. This was confirmed by one of the authors.
To conclude this workshop it was decided to continue discussions a as a forum set up on the EAFP website. This can be found on eafp.org under the message board.
Prague Workshop