Thursday, August 10, 2006

Latest bTb figures

"There has been a substantial reduction in the number of new TB incidents in January - June 2006 compared to the same period in 2005. The provisional statistics presented here indicate that this reduction is 19%, although this figure will reduce as further test results are input by AHDOs. It is too early to draw any conclusions about whether the decrease is a temporary or a more sustained reduction and further analysis is needed to identify the reasons for the fall. However, it is likely to be caused by a complex combination of factors. There is no evidence at the moment that the switch in tuberculin supply has caused this reduction although further analysis is required before this can be confirmed."


If this paragraph seems familiar, then that is because it has been used in the last three months to express Defra's comments on its monthly bTb statistics, posted on the Defra website. The only difference in wording being the percentage drop: "April : 27%, May: 20% and now June: 19%." but these statistics are are an amalgum of several months, from which it is difficult to see the whole picture. And we would respectfully point out, produced by a department who comfortably airbrushed out almost 50% victims of its FMD culling spree.

So what is the story behind the figures? For sure 'other influences' will have had an effect. But how much? Two blazing hot summers will influence the time that m.bovis survives on cattle grazing ground, but the same dry hot weather will put badgers under stress as the ground is too hard to dig, and natural water supplies short. Any infectious disease has a 'bell curve' of a rise in cases, followed by a drop, and tuberculosis may have peaked in the badger population and be waning. Even farmers may have reached the end of their tethers and with the introduction of tabular valuations, be sorting out their own badger / cattle bio security. But all these factors, would have had to have happened together and at the same time last autumn, for the skin tests (for that is what Defra's statistics are based on) to have shown such a dramatic change early this year. And even this is only half the story.

Further analysis of the past 4 months are interesting. Defra's headline figures are for 'New Herd Incidents'. That is herds at a routine test, which were classed as 'clear' and are going under restriction for the first time. It is these herds which saw the drop of almost 30% in Jan - March, then 27% Jan - April, 20.2% Jan - May and 18.7% currently Jan - June. But what of Defra's other figures?

Cattle slaughtered over the last 4 months are consistantly over 30% less than 2005. (Range 36.6 - currently 33%) That is good news, but slaughterhouse cases, that is cattle found by MHS examination are up by much more than that. Range +75% - +35% currently.

Herds under Tb restriction through a bTb incident (as opposed to overdue test/data) are steady at between 1 - 3% less than last year. So although the new herd incidents are down (or not being found) the herds under restriction figure has barely changed. Jan - March -1%, Jan - April -3,5%, Jan - May - 1.7% and currently to June -1.9%, so they are not being cleared.

But the bad news behind this headline is that herds registered on Vetnet, from which Defra draw their statistics, are down too, so the percentage of herds under bTb restriction is actually UP on 2005. Jan - March 3.65% (up +0.05%) Jan- April 4% (=) Jan - May 4.33% (+0.03%) and currently Jan - June 4.55% (+0.02%)

So, a huge drop in February / March in new herd incidents , while not sustained but is still dramatically less than last year: cattle slaughtered are consistantly down over one third for each of the last 4 months - but slaughterhouse cases up by at least the same amount. The total number of herds under restriction, barely changed while the percentage of these herds, drawn from total registered herds is up. And just to throw a real spanner in the works, in February some AHDO's sent out a 'Revised bTb interpretation chart- TB64 02/06', to their local vets.

This indicates a marked tightening up on interpretation of the skin test, with zero tolerance to any oedema at all in the area jabbed. Below a 2ml rise on skin thickness, even '0' and '1' ml are classed as IR or Reactor, whether or not they matched by an avian rise of the same type. 2ml can be the difference between a Pass and an Inconclusive, or an Inconclusive and a Reactor.

Although we have no grounds on which to base this comment - yet - we suspect that Lelystad tuberculin has given a slightly different reaction from the UK serum, a fact that VLA have only just caught up with. It maybe also strain specific, in that our UK serum identified some or all of the UK strains better. And we also suspect a completely duff batch - for whatever reason - sometime after Christmas which accounted for the precipitous fall in Jan - March. Time will tell.

But as far as International Trade goes, while our herd incidents are at 4.55% of the national herds and rising, we are as far away from Tb free trading as ever.

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