Friday, September 08, 2006

Latest stats

Defra have published their latest statistics for Tb incidence, available for a short time at:

This link will only connect to Jan - July as long as these figures remain. When Jan - Aug are posted, the link will show the updated statistics.

Briefly, the upward trend continues, or the downward trend has not been maintained - depending on your point of view.

Our analysis so far:

The Jan - March figure which caused all the fuss, showed a drop of almost 30 percent in New Herd Incidents (NHI), but herds under restriction was steady at only 1 percent down on 2005, and this as a percentage of herds registered, was slightly up at 3.65 percent. Cattle slaughtered were down 35 percent and slaughterhouse cases (as reported) was up 75 percent.

Jan - April : a drop of 27 percent in NHI but herds under restriction down just 3.5 percent, which as a percentage of herds registered on Vetnet was down very slightly. Cattle slaughtered still showed a 36 percent drop on 2005, and slaughterhouse cases we were unable to tabulate the change (typo)

Jan - May, the pattern was the same: A drop of 20 percent in NHI (so rising again) herds under restriction down just 1.7 percent, and this as a percentage of herds on Vet net up. Now at 4.33 percent. Cattle slaughtered still showing a 32 percent fall, and slaughterhouse reports up 50 percent.

Jan - June. A 'drop' of 18.7 percent in NHI, but herds under restriction down just 1.9 percent. This figure as a percentage of herds registered, slightly up, and cattle slaughtered still a third lower than 2005, with reports from slaughterhouses up 35 percent.

And the current figures continue this pattern:
Jan - July. The 'drop' in NHI has now reduced to 14 percent lower than 2005, and Defra are no longer flagging it up. Herds under Tb restriction remain slightly below last year at just 0.4 lower, and this as a percentage of registered herds is now 4.82 compared with 4.73 in 2005. Cattle slaughtered are still a third less than last year - 32 percent lower, while cases reported by MHS from slaughterhouses is up 36 percent.

For the record ( and members Her Majesty's Opposition, should they care to look before offering their opinions to the press in a burst of opportunist, lightweight spin (see post below)}:
391,822 more cattle were tested during this period, and 4,500 more herds than in 2005 - an increase of almost 17 percent.

Nothing we have seen from these figures, can we interpret as a substantial drop in bTb. The one 'constant' is the drop in numbers of cattle slaughtered, which are consistantly one third lower than last year, in every period from March. So we stick with the opinion that the Dutch Lelystadt tuberculin, while not a substandard product, is different from the UK produced antigen. And the more we scan the CVO's statement on it, the more we see that all the dots are in fact joined. The statement comments on the numbers of VL animals between the two products thus:

"The comparison of the tuberculin data, indicates to date that a proportion of VL animals [ ] differs significantly between Weybridge and Dutch PPD batches, with the Weybridge results having a smaller % of VLs.

The authors say that there are two ways of interpreting this, but conclude that the following is most likely:

"The sensitivety of the combined Dutch PPDs is less, because of failing to pick up NVLs (animals which could be in the early stages of disease) which may or may not be confirmed with culture, to the same extent as Weybridge PPDs. This would result in underdetection of cases, resulting in a transient decline in cases reported, despite there being no true decline in cases."

Precisely. The incidence of bTb is not dropping significantly, but the incidence of its detection, especially in the early pre visible lesion stages, is.

No comments: