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Įdomybės Konferencija skirta KOI HERPUS virusui sustabdyti
Konferencija skirta KOI HERPUS virusui sustabdyti |
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Konferencija skirta KOI HERPUS virusui sustabdyti buvo surengta...(en). Šaltinis: www.practicalfishkeeping.co.uk A number of the worlds top experts on fish diseases gathered at the second Ornamental Aquatic Trade Association (OATA) conference recently to discuss how the trade should control what is now regarded as the greatest threat the aquatic industry has ever faced Koi Herpes Virus (KHV).The highly virulent disease, which was first isolated in 1996 in the UK, is believed to have been present in carp populations for some time before it was formally recognised and described. Since then, it spread around the world from Germany, Israel, South Africa, Malaysia, Hong Kong and Indonesia to Taiwan, and most recently, to Japan, where it has caused massive mortalities among food Koi. Since autumn 2003, the disease has spread to 38 of Japans 44 prefectures. The UK has also not escaped the disease, with over 100 reported cases in the past few years, and the number of unreported or undiagnosed cases undoubtedly standing much higher. Its not yet known where the virus originated. Dr Keith Way, Senior Virologist with the Cefas Weymouth Laboratory, and a specialist in Koi Herpes Virus, told delegates at the conference that since the outbreaks in Japan there had been a new impetus for research into the disease. Dr Way explained that Japanese scientists have now sequenced the viral genome of the Israeli, Japanese and USA strains of the disease, and have been developing more sophisticated detection methods based on polymerase chain reaction (PCR). Likewise, Cefas has been working on detection methods and PCR optimisation, thanks to a grant from OATA and Defra, as well as undertaking carrier studies and investigating enzyme linked immunosorbent assay (ELISA) methods for finding antibodies in carriers. American virologists have been looking at the distribution and concentration of the virus in fish tissues and comparing the virus to other cyprinid viruses, and the Israelis have been continuing their work on studying resistance and detection of the virus. According to Dr Way, Defra now considers KHV a high priority for further research. Fish farmers fight back Its not just scientists who are working to tackle the disease. The fish farmers themselves are also working actively to ensure that KHV doesnt destroy the trade. Last year, South Africa saw its first major wipeouts from KHV and one farm culled over 100,000 pounds worth of yearling Koi to prevent the carriers being passed on. Dr Ralph Knussel, a post-doctoral researcher at the University of Stellenbosch, has been working with fish farmers on one of the affected farms to help them to recover their business and protect themselves against further outbreaks of the virus. According to Dr Knussel, the technique they are using basically relies on a conscientious approach to biosecurity. All of the ponds on the affected farm were disinfected with chlorine, limed and left to dry for 2-3 months, during which time the brood stock fish had been kept separately. No carriers or wild carp were allowed on the farm and any new brood stock was rigorously quarantined and PCR tested before being introduced. The farmers even erected huge bird nets over their ponds to prevent fish-eating birds entering the pens and spreading the virus on their feet. Following spawnings, the eggs were disinfected using Betadine, and the fish and offspring retested. By culling any fish that gave positive PCR results for the presence of the virus, the suppliers had a good chance of being able to say that the fish were free of the disease. Deliberate exposure In stark contrast, rather than trying to keep the disease out of their farms completely, and therefore produce fish which have almost certainly never come into contact with the virus, the Israelis are actually exposing their fish to KHV. When the virus caused mass mortalities in the carp farming community of Israel between 1998 and 2000, the trade there was fast to react and has been pulling out all the stops to prevent it from destroying their industry. The Israelis are intentionally infecting fish that dont carry the virus (so called naive fish) with KHV under controlled conditions and producing fish that they say are resistant to the disease, without actually being carriers themselves. The technique is not short of its critics. Some experts believe that the Israeli fish could pose a risk to naive fish. However, many people in the trade believe that this may be the technique to adopt, and arent experiencing problems with imported fish, or with the disease being passed on to naive fish in their wholesale and retail ponds. The UK reaction In the UK, back in 2001, OATA produced a series of guidelines for the trade to follow which involve quarantining new fish in isolation and exposing them to a temperature of 23-28 C for over 14 days. Since the virus has been shown to become latent when the water temperature is low, when fish neither exhibit symptoms nor die, its quite feasible that apparently healthy carp could be mixed with naive fish and transfer the disease to them. It may only become apparent when temperatures rise that any of the fish are harbouring the virus. OATAs technique should allow the presence of the disease to become apparent in any new fish so further action can be taken to contain the disease. The most responsible retailers and wholesalers were quick to adopt OATAs suggested actions for KHV, but unfortunately there are still some who choose not to follow them, instead relying on the fact that their supplier should have done this, which is seen by some as a potentially risky thing to do. The International Workshop on KHV held in London in 2004, led to the development of another UK-based attack against the spread of the disease the Koi Biosecurity Institute (KBI). Nigel Cohen of the KBI explained that the system adopted for this open register was similar to the one used by chartered accountants. It allows transparency so potential clients can see, via the results of an audit or self-assessment, exactly what measures a company has introduced to control the spread of the KHV (and other diseases) through good fish management practices. The KBI is still in its infancy and so far only 60 businesses have paid the administration fee (£50) required to sign up. Of those, only 20 are based in the UK. In an area of the trade that has seen one high profile, and high cost, legal case concerning the sale of KHV-infected fish, the KBI hopes that the register could provide a strong defence case in the event of legal proceedings. Some critics, though, see the publication of their poor biosecurity status, or the presence of KHV in their stocks, as too large a risk to take. The hope is that trade demand will eventually encourage buyers to demand to know the biosecurity status of their suppliers, forcing the trade to raise standards, so retailers and consumers can be more confident of purchasing healthy fish. Figures from Cefas announced at the OATA conference suggest that this year theres been a significant drop in the number of cases of KHV in the UK, with just five out of 21 tests proving positive, compared to around 36 of 74 tests in 2003. However, the introduction of a testing fee of several hundred pounds is almost certainly responsible for the drop this year, which may mean that in future years the true extent of KHV in the UK wont be known. While similar viruses, such as Spring Viraemia of Carp (SVC) are notifiable, making it a legal requirement to have suspected fish tested and for movement restrictions to be imposed, there are currently no such measures for KHV. As a result, the true extent of the disease is going to be difficult to quantify. Its possible that Defra may introduce tighter controls against KHV in the next few years, which could potentially have a serious impact upon the fish trade. The trade needs to continue to work hard at preventing the further spread of this highly contagious disease. This article was first published in the January issue of the trade magazine Pet Product Marketing. |
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