For a short time only, Defra have posted the Tb statistics for January - November 2006.
Defra describe the results thus:
"There has been a provisional 7% reduction in the number of new bTB incidents in Great Britain in January to November 2006 compared to the same period in 2005. There was a considerable drop in the number of new incidents in the first four months of 2006 compared to 2005. However, since May the number of new TB incidents reported in 2006 was slightly up on 2005. As a result, the percentage decrease in new incidents reported in previous months has now reduced" .
From March, when the drop in New Herd breakdowns was almost 30 percent, the fall (and thus increase) in bTb incidence has reduced and now stands at 7.2 per cent lower than in 2005 at the same time.
We have tracked these results with a great deal of scepticism, and reported our thoughts regularly. The immediate candidate for the fall was the substitution from September 2005 of our own UK produced 'Weybridge' tuberculin antigen with a product made by Lelystatd in Holland, which although a similar product, was found in the CVO's report to have given "a small but statistically significant difference" in performance. Annex C of the same report described the difference thus:
"The sensitivety of the combined dutch PPD is less because of failing to pick up NVLs ( animals which could be in the early stage of disease)... [ ] This would result in underdetection of cases, resulting in a transient decline in cases reported, despite there being no true decline in cases."
We covered this at http://bovinetb.blogspot.com/2006/08/going-dutch-2mm-difference.html
At the time of the CVO's report, the authors, despite blaming their veterinary practitioners for jabbing the cattle in the wrong way (Have they all been retrained? All of them? Really? Wow..) leant towards this explanantion, but is it the whole story? For figures to be comparable, the root raw data must be from the same source, and in this case it is not.
Data in the past has been drawn solely from routine tuberculin skin tests. For sure, as bTb increased, so did the skin tests as more and more parishes fell under annual regimes.
And over the last two years, Defra has come down hard on the cattle side of bTb - short of the obvious of course, and that means testing annually every herd in the country, but let that pass.
Parish testing intervals have been extended outwards, drawing more farms into more regular testing, but also farmers' own pre movement testing results will build into these figures, giving a further increase in herds and cattle tested which was not in the data from 2005 or prior to that. Defra are compunding this increase with a 'hypothetical drop' of around 23 percent in bTb, given the increase in testing. Into this mish mash of figures add gamma interferon, now in use in all areas but under different circumstances, and the picture is even more muddled.
It is our understanding that in areas of annual and two year testing, a third time IR skin tested would only result in around 15 percent failure rate. But those animals now get no third chance; after two Inconclusive tests, gamma interferon is routinely used. And it is giving a failure rate of 50 percent. For what reason we can only repeat previous info. That this diagnostic test is different, picking up antibodies to bTb in the animal's blood and that it is much less 'specific' than the comparative skin test. We understand that it is confusing, amongst other things paratuberculosis (Johnes disease) which may or may not be a good thing - but when lumped together in a bTb statistical context, is misleading. Many will argue, probably quite rightly, that in a hot spot situation, many cattle will have had a small exposure to m bovis, and thus need a higher exposure to provoke either the disease itself, or a skin reaction to it. But Gamma interferon will take out exactly those animals who have acquired this degree of immunity. For more see: http://bovinetb.blogspot.com/2006/11/new-leaflet-farmers-would-prefer-not.html
And then there is the weather. Blazing hot sunshine - with associated ultra violet - is the single most lethal influence on m.bovis. And we've had two consecutive summers, where its survival on grassland has been severly curtailed- to the benefit of any grazing cattle who may encounter it. The downside of the heat and the hard packed ground, is hungry badgers, foraging this summer, we hear, in farm buildings. The results of which will only show up in cattle tests this winter and into the spring.
But we are aware that with all these different data streams into the statistics, it is very difficult to compare. So we will concentrate on the figure which draws the attention of our trading partners. Bearing in mind that to achieve OIE 'Tb free' trading status, the number of herds under Tb restriction in a given period must be less than 0.02 per cent of herds registered on the country's database, the only thing we see, is that headline figure of GB herds under bTb restriction as a percentage of herds registered on Vetnet, is UP.
To November this appalling figure stands at 6.10 percent. An increase of 0.2 on last year.