Wednesday, May 19, 2010

Shrinking halos ?

During the RBCT Badger Dispersal Trial's 8 night, very infrequent hit-and-run excursions into TB infected badger populations, the ISG's computer models logged an increase in cattle TB in the areas surrounding the 'clearance' zones. These 'halos' were offered as an argument for doing nothing, as they had appeared to make matters worse for cattle herds surrounding culled areas.

The fact that in previous decades of GB's progressively sanitised badger removals, no such 'halos' appeared around areas (large or small) which were culled out adequately, seems to have escaped the great and the good of the ISG. As did the change in RBCT protocol after the first 4/5 years of chaos, which meant that they did actually achieve some sort of a clearance as we reported here.

This was reflected in the Jenkins paper, published in 2008 which we discussed here. The ISG team requested more government cash work, and they were able to continue to log cattle breakdown data from the RBCT areas for a longer period of time. The team of scientists and statisticians undertaking the follow-up work to the RBCT trial have published again updating data on the impacts of cattle TB incidence of repeated badger culling

This additional data has been further analysed as a comment on a scientific website by one of the team, Prof. Christl Donnelly.

Since publication of the paper “The duration of the effects of repeated widespread badger culling on cattle TB following the cessation of culling”, (see abstract here) an additional six months of cattle testing data have become available. These allowed analyses to be updated.
In the time period from one year after the last proactive cull to 31 January 2010 (the post-trial period), the incidence of confirmed breakdowns in the proactive culling areas was 37.0% lower (95% CI: 25.3% to 46.8% lower) than in survey-only areas and in areas up to 2km outside proactive trial areas was 3.6% lower (95% CI: 29.0% lower to 31.0% higher) than outside survey-only areas.

"Exploratory analyses stratified by 6-month periods (Table 1) suggested, unexpectedly, that the beneficial effects observed within trial areas in the first year post-trial, have reappeared in the last 6-month period analysed (37 to 42 months post-trial)."

"These latest results are consistent with a constant benefit of proactive culling continuing through this latest period. However, the effects observed outside trial areas are consistent with no ongoing effects of proactive culling in these areas."

"There is no clear explanation for the unexpected pattern observed within trial areas based on these latest data. (We examined parish test intervals and they are very similar in and around proactive and survey-only trial areas.) Continued monitoring is necessary to quantify any further temporal changes in the effects."

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.

So, a begging bowl extended for 'more monitoring' ? - that was to be expected.
But no halos? And the excuse for doing nothing goes where, exactly?


Anonymous said...

Minister blocks cull of badgers in bovine TB hotspots

From The Times
May 20, 2010

Valerie Elliott

Plans for an emergency cull of badgers in hotspots of bovine TB are to be delayed while Caroline Spelman, the Rural Affairs Secretary, reviews the scientific evidence.

Ministers will also await the outcome of a pilot cull in West Wales before embarking on such a policy in England.

The decision will disappoint many farmers, especially those in areas with highest incidence of the disease, such as the South West. A further review is surprising because the Conservatives and the Liberal Democrats supported an emergency cull of badgers during the election campaign. The Conservatives have always seen vaccination as the eventual breakthrough to control the disease, although before the election Jim Paice, the Agriculture Minister, met officials at the Porton Down research establishment to see if it is possible to test badger setts for infection before any animals are killed.

It is also unclear what message this sends to the shires, especially as the Government has already kicked into the long grass a free vote for MPs to repeal the hunting ban. Giving people the freedom to hunt has become as totemic an issue for the Tory faithful as it was for the Labour Party to ban the bloodsport.

Senior figures at the Countryside Alliance, however, had prepared the ground well before the election result to dampen expectations for an early resolution on hunting. No one expected hunting to be a priority issue especially at a time of economic crisis.

Simon Hart, former chief executive of the alliance and the newly elected Conservative MP for Carmarthen West, said: “As far as I am concerned there is no change in the position and the commitment to offer a vote on repeal is solid. Frankly it is a matter of trust between the Government and hundreds of voters and I am not going to get indignant about having to wait for another few months or for another year or so.”

He said that a year ago many in the hunting world had not even expected the chance to repeal to be included in the Conservative manifesto but the commitment was ”a significant step forward”.

He admitted there may be some impatience in some quarters and there would be anger if the commitment were dropped altogether. “But that is not the case. It will be done, it is when, not if. When the important issues of budget deficit reduction are sorted we’ll get a Parliamentary slot and deal with it.”

Three men were arrested yesterday after officials were stopped from entering land to prepare for a badger cull in West Wales. A police spokeswoman said the men were later released and no action will be taken.

Matthew said...

Anon 9.00
Thanks for the link. We have a few more - all contradictory. New post up with a few quotes.

Anonymous said...

1. It wasn't "the ISG's computer models" that identified increased herd breakdowns on farms surrounding the proactively culled areas; it was direct observation (i.e. recorded breakdowns), just as it was direct observation that identified the reductions inside the culled areas.
2. The reason why "no such halos appeared around areas...which were culled out (in previous culling operations)" is simply because no one looked for them!
I quite accept that you adopt a one-eyed approach to badger culling, but it would help understanding amongst the more open-minded of us if you reported things accurately.

Matthew said...

anon 11.32
1. That they used actual data in the mathematical models is to be applauded. It makes a change as it was ignored in the TB99s so faithfully filled in by us all - and then superceded by a 'rough assessment' using 'assumptions of of 2 parts cattle v. 1 part badger'. (ISG Final Report 7:24)

2. If perturbation 'halos'had been the case over the previous 3 decades of progressively sanitised strategies, AHOs are sure that they, the farmers concerned and their MAFF / Defra ministers would have noticed.
Just because a 'scientist' (loosely worded) hasn't written something up, it doesn't mean it did not happen - or in this case that it did.

Take out a few badgers on an occasional short burst, scatter the group and remove the dominant scent markers and for sure the applecart is upset. Take out the whole group, quickly and no such phenomenon occurs. This was unique to the RBCT, and predictably so.

Krebs original protocol for the RBCT recognised the dangers too:
(See 7.8.4 ii)

7.8.3 The gassing and clean ring strategies, in effect, eliminated or severely reduced badger populations from an area and appear to have had the effect of reducing or eliminating TB in local cattle populations. The effect lasted for many years after the cessation of culling, but eventually TB returned.

7.8.4 The interim strategy, introduced following the Dunnet report, is not likely to be effective in reducing badger-related incidence of TB in cattle for the following reasons:

(i) The policy involves removing badgers from a limited area (the reactor land or the entire farm suffering the herd breakdown if the former cannot be identified) ; but social groups of badgers may occupy several setts covering more than one farm.

(ii) Partial removal of groups could exacerbate the spread of TB by peturbation of the social scructure and increased movement of badgers.

(iii) There is no attempt to prevent recolonisation by badgers of potentially infected setts; even if infectivety in the setts is not a problem, immigrant badgers may bring new infection.

The relevant bit, in case you missed it:

ii) Partial removal of groups could exacerbate the spread of TB by peturbation of the social scructure and increased movement of badgers.

So, why cull for just 8 nights, very occasionally and put up with almost 70% of the sited traps either intefered with or disappeared, Dec 1998 - Oct 2003?

What better way deliver exactly what Krebs warned against?

George said...

Looking at the distribution of disease cases in space and time is an epidemiological technique that is frequently used and the patterns discovered can reveal a lot about the characteristics of a disease. TB is no exception. I was working for Animal Health at this time, and this is how we discovered that cattle TB cases were clustered in space and time. So the pattern of disease cases was being looked for during the various badger removal strategies, and we would definitely have noticed if clusters of new cases were appearing around the areas where badgers had just been removed. This phenomenon was not observed.