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TSEs and Bluetongue in the UK - where are we now? |
 
Who saw this article? New!
Author: Paul Roger - Courtesy of Nottingham University Press
Abstract presented at the 41st University of Nottingham Feed Conference. Our deep appreciation to the authors and the kindly cooperation of Prof. Julian Wiseman, Professor of Animal Production / Head of Division Division of Agricultural & Environmental Sciences, School of Biosciences a the University of Nottingham.
These two very different diseases present threats to our livestock industry in different ways. Control methods are difficult and imprecise but the overall approach needs to be consensual with all the relevant “stakeholders” contributing to an agreed strategy based on a sound scientific approach and recognising the finite means available for disease control. The TSEs that occur naturally include diseases that affect Man.
The unknown nature of the infective transmission of these diseases creates concern as the primary control is through genetic selection for decreased susceptibility. That is, genetically resistant stock do not express clinical disease but they may do if they live long enough – the resistance is to development of clinical disease rather than to disease itself.
Because of the lack of a measurable immune response, vaccination is not a possible option for prevention and there are no preventive or therapeutic treatments available to treat affected animals.
Symptoms vary but develop in the final stages of disease and include trembling, pruritus and increasing incoordination.
Diagnosis can only be carried out post-mortem.
Presently control strategy has been aimed at selection of the more resistant genotypes and a discarding of the 2 most susceptible genotypes aiming to produce lamb containing at least one of the most resistant genes for the meat trade thus trying to reduce the tiny chance of TSE transmission into the human food chain.
This picture has been complicated by the emergence of atypical scrapie – a new form of the TSE – identified by post-mortem surveillance of CNS in sheep. With this form there are no reported clinical signs and all genotypes appear susceptible.
The EU and SCoFCAH have advised increased surveillance but this has had the effect of suspending the drive towards prohibiting the use of the previously recognised high risk genotypes.
Bluetongue is an arthropod-borne viral disease of ruminants. There are no zoonotic implications. There are 24 different identified serotypes causing differing symptoms but all depending on the presence of competent vectors for spread of disease.
In 2006, BTV 8 arrived in Northern Europe, a jump of some 700km from where it had previously been known. In 2006, the disease spread in Northern Europe and has worryingly recrudesced this season with large numbers of infections being reported daily. The symptoms which are classically reported as being worst in sheep with cattle often as symptomless carriers are seemingly more severe in this naďve population and cattle often show severe symptoms. Recently the clinical disease has also been seen in goats.
The wide range of signs make it difficult to recognise an index case as similar symptoms can be seen with a number of other diseases including photosensitivity (and FMD).
Control is fraught as insecticides are not particularly effective at controlling Culicoides spp and C. dewulfi which has been identified as a vector is found inside buildings as well as outside.
Vaccination with a specific vaccine against the strain may be a useful weapon but this is still in development and the frightening prospect that the Industry may need to live with the disease is looming.
Raised awareness of the risk of entry of the disease and a paramount concern to identify the primary incursion of disease are major priorities in present control. Surveillance of susceptible imports is important but as Culicoides spp travel as the “plankton of the air” a credible and cost effective active surveillance at potential land fall sites would be useful.
Author: Paul Roger
Veterinary Consultancy Services, Reeth, Richmond
Author: Paul Roger - Courtesy of Nottingham University Press
Who saw this article? New!
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ENGOREART OVI 20080515
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