Sunday, April 29, 2012

Not the Final Report.

Since the Badger Dispersal Trial RBCT ended in 2006, producing its bible in 2007, we have been extremely critical of its published results. Not without cause, as many of our contributors had the misfortune to be caught up in this charade of 8 nights well publicised and vandalised cage trapping, once a year if you were lucky.

On reading the Final Report, it became apparent that far from using information contained in the painstakingly time consuming TB99 forms - each of which was a ream of paper dealing with risk, prepared by trained veterinary officers with back up from several government agencies - the ISG chose to ignore what was airily described as 'apocryphal' evidence.

The personnel completing these forms for the RBCT, are highly trained veterinary practitioners, with back up support for the data from government agencies such at the British Cattle Movement Service (BCMS), Cattle Tracing Service (CTS), Ordnance Survey office and Veterinary Laboratories Agency (VLA). So it was a wasteful, arrogant, disgrace disappointing to realise that far from actually using this robust, complex, epidemiological data, the ISG chose to ignore it. But worse than that, within the section concerning the spread of tuberculosis in cattle, the ISG describe their epidemiological base, stating that they included:
"........ local infection across farm borders, infection from animals bought, in particular but not only, from high incidence areas and infection from wildlife, especially badgers. [] In the following calculations, we assume all three sources to be roughly equally important." (ISG 7.24 p148)
Thus the ISG chart would appear like this .... :

... because far from using that robust, complex epidemiological data contained in these forms to actually see what was going on, the ISG 'roughly assumed' two parts cattle, one part badger, pumped that into a mathematical abacus and switched on.

Since then two further reports have been published. The first from Jenkins et al, in 2008 which found that the notorious 'edge effect' of increased TB incidence associated with the fiasco that was the first couple of years of the trial, had reversed in subsequent years. The paper looked at the trial data for each of the years in which it tried to cull badgers, and then ran the TB incidence in cattle data onwards for each of a further two years at Defra's request and taxpayer's cost. As we explained in the posting:
The estimated effects on cattle TB of culling badgers within the cull areas during the trial increased over the time frame from a modest 3.6 percent in its first year, to 31.8 percent from the 4th to final year. But two years later that effect had increased to 60.8 per cent. Conversely the 'edge' effect, unique to the ISG 8 night cage trap fiasco, caused 43.9 percent increase in breakdowns up to 2 km outside the triplet zone in the first year of culling, falling to 17.3 percent in the 4th - final year's scrape up. But within two years, that negative effect had somersaulted to a (minus) -30.1 percent incidence outside the proactive zones..
Further work from Prof. Donnelly followed in 2010 which showed that the cull areas, had maintained that benefit. That paper explained:
This updated data shows that in the period starting one year after culling stopped up until 31 January 2010 the incidence of confirmed breakdowns in the proactive culling areas was 37% lower than survey only areas (areas which were surveyed but not culled). Furthermore in the areas adjoining the culled area the incidence was 3.6% lower. This means that any initial perturbation effect has been quickly overturned and there is now a lower than previous incidence in these areas.
Now Prof. Donnelly has turned the power on again, and come up with a rather interesting conclusion using the post mortem results of the trapped trial badgers - or those they did manage to cage trap in 8 nights, very occasionally with time out for FMD:
The observed and model fitted per-herd incidence of confirmed TB herd breakdowns within each proactive trial area and the corresponding estimated proportion of confirmed TB herd breakdowns attributed to infectious badgers. The observed data related to 12 months prior to the initial proactive cull (so a different 12-month calendar period in each case). The fitted values were obtained from a model, fitted by Donnelly and Hone (2010), to the relationship between the incidence of confirmed TB herd breakdowns and the prevalence of M. bovis infection detected among badgers culled in the initial proactive culls.
Prof. Donnelly's results show that within the triplets, two areas had cattle breakdowns of up to 72.7 per cent 'attributed to infectious badgers'. A further two attributed 60.6 per cent to infectious badgers, four between 41 and 49 percent and the last two (where from bitter experience, much interference took place) 16.8 - 32 per cent.

We are grateful once again to use these images, both first shown at the Killarney Conference. But hey - 72.7 per cent of cattle breakdowns 'attributed to infectious badgers'? We note that with each publication, Prof. Donnelly's electrical abacus is catching up with the reality and effect of TB infected badgers.
Perhaps the ISG would care to redraft their 'Final Report' of 2007?

No comments: