THE GOAT VETERINARY SOCIETY |
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ERADICATION OF VIRUS
It was fascinating to hear a presentation form Professor James Machlaclan, who has worked on BTV within the University of California, for 30 years. As he said, in Europe we have had ten incursions of Bluetongue in the last ten years. In the USA they have had TWELVE, albeit mainly in the Gulf, ie Eastern, states. James was asked about eradication, and gave the fascinating opinion that in the USA, where disease had been eradicated on a state by state basis, it was usually when only one strain of BTV was involved. Where two or more strains were involved, it became a lot more difficult. BTV8 seems to be one of the most virulent strains known, especially in cattle.
SITUATION IN FRANCE
The French Authorites claim to have had a successful campaign of vaccination during the spring of 2009, but that varies from some reports in the field, which suggest that a lot of farmers have only vaccinated their young stock against BTV8 on the distinctly doubtful principle that the older ones probably immunised themselves last year. It is interesting to note that while the sales of BTV1 vaccine in France appear to be close to the number of livestock that can be targetted, sales of BTV8 vaccine are running at only half of that level, though of course a lot of cattle will only have needed 1 dosed this year rather than two. The main concern seems to be widespread failure to vaccinate sheep again.
Herge Petit presented the results of a study at L’Iinsitut d’ Elevage in France, on the economic effects on farms affected in France as a result of BTV in 2007. 2008 information is still being collated. Costs such as production loss, deaths, veterinary fees etc were all included in the study, in which he subdividedthe herds studied into mildly, moderately, and severely infected, though without stating the details of the criteria. Suffice it to say that he calculated the reduction in gross margin in dairy units as being 1.1%, 6.6% and 8% respectively. In beef suckler herds these figures rose to 6.1%, 8% and 17.7% respectively. For sheep the effects were dramatic. Only a 4% reduction in mildly affected flocks, but 50% in moderately affected flocks, and
106% in severely affected flocks.
It was interesting to note that a far greater percentage of bulls were affected than cows, but this may have been a statistical quirk of a small sample.. There was a report on fertility in affected rams in Holland in 2007, which is interesting in that affected rams produce substandard sperm after getting the disease, but recover normal production by 60 to 140 days after. That however tends to mean missing a breeding season as the timings work out. We have as yet no figures for bulls, and have to assume that bucks would behave as rams!!. Some seropositive or PCR positive rams that had shown no outward signs of disese became temporarily infertile.
Situation in 2009 and Other Points
Vaccination Transmission Transplacental Eradication Current situation