Monday, June 09, 2008

Patience......

Tuberculosis testing of cattle may not show the results either of exposure to m.bovis, or the removal of its source, for several months. So after the RBCT Badger Dispersal Trial staggered to a halt, the full results would be not seen until the next routine test of the cattle herds which were within the triplet areas.

John Bourne was keen to stress that his 'edge effect' (that is the peturbation of shattered social groups of badgers caused by his hit-and-run eight night trapping forays) was a very good reason not to do anything at all with the wildlife reservoir of bTb in this country. But while Bourne is concerned about his 'edges', others have rechecked the data from the trial and found that over time:
Beneficial effects inside culling areas increased in magnitude and detrimental effects were no longer observed on neighbouring lands,

This study of the longer term effects of the ISG's trial was seen as fresh evidence that a cull of badgers in in high-risk areas can be successful at reducing disease incidence in cattle. This is the conclusion of a report from the International Society of Infectious Diseases, which found that the beneficial effect of badger culling on cattle herds lasted for in excess of twelve months, while the 'perturbation effect' so beloved of the ISG, faded rapidly.

Farm Business has the story. Sorry, no direct links (yet).

UPDATE

We have now had sight of the paper and can offer a few more quotes.
Elsevier - a subscription site - has it on web link and state they publish on behalf of the International Society for Infectious Diseases. The paper was received March 20th 2008, received in revised form 3rd. April 2008 and accepted for publication 9th. April 2008 in the society journal, the International Journal of Infectious Diseases.

The lead author is to be cited as 'Jenkins, HE et al. The et al being Rosie Woodroffe and Christl Donnelly - late of ISG fame. The title "The effects of annual widespread badger culls on cattle tuberculosis following the cessation of culling.

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.

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.

Conversley the 'edge' effect, unique to the ISG 8 night cage trap fiasco, caused 43.9percent 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 somersualted to a (minus) -30.1 percent incidence outside the proactive zones.

The summary results:
"During the post trial period, cattle TB inside culled areas was reduced,[] to an extent significantly greater than during culling. In neighbouring areas, elevated risks observed during culling were not observed post trial [].


And concludes:
Although to-date the overall benefits of culling remain modest, they were greater than was apparent during the culling period alone. Continued monitoring will demonstrate how long beneficial effects last, indicating the overall capacity of such culling to to reduce cattle TB incidence.


Update (2) The paper's author and a link to her work - an extension of the ISG results - can be seen here

The number of cattle slaughtered in GB increased from just 638 in 1986 to 3,760 in 1997 during the so called 'Interim Strategy' while government were making up their minds who was pulling their strings. Then a £1 million bung from the Political Animal Lobby brought a moratorium on badger culling in response to outbreaks of confirmed bTb, which has remained - hidden under the skirts of the RBCT.

During the following decade, cattle slaughterings rocketed to a staggering 28,175 in 2007. And 2008 is on course for another 20 per cent increase.

The NFU is using the ISID report to re-issue a call for the Government to finally make up its mind and allow selective culling to target TB hotspots in England and Wales. GB's 'patience' is running out....

8 comments:

Anonymous said...

You say that "others rechecked the data from the trial". Did you actually look at who the authors of the paper were before you wrote this?
Or even care to look at the actual contents of the paper, which time period these results and conclusions related to and whether or not the data were "rechecked"?
Maybe you should do some rechecking of your source before stating anything that might mislead your readers.....

Matthew said...

Anon 11.19

We said in the post no links - yet.
The 'source' of the story is one of two independent farming press articles (one of which we linked to) which quote this particular report by the ISID.

Data from the trial (we understand from the articles) was revisited twelve months (at least), after the end of the trial - with rather different results from those published by the ISG.

If and when we are able to post more and a direct link to the report, we will update and do so.

George said...

It should come as no surprise that the beneficial effect of reducing the disease reservoir would still be evident after some time. TB in cattle did not return to the Thornbury area for years after the badger removal there.

Anonymous said...

matthew 7.25

So you said that "others" rechecked the data without checking who the authors were. The paper was published by the International Journal of Infectious Diseases which is a journal of the ISID therefore it is not a report BY the ISID. They did not write it, one of their journals published it.
Secondly, yes, data from the trial was revisited more than 12 months after the end of the trial. Those published in the ISG's final report were using results from the end of the trial. Therefore it is perfectly possible that both the ISG's results were correct - as of the end of the trial - and that something further has happened since the cessation of culling. Both sets of results could be correct - for the time period to which they relate.
Tell me, what does the published paper say about this?
Oh no, you haven't read it yet. Please read the paper for yourself and then let us know whether everything you said in your blog article was correct. It's a good idea to check your source before quoting others blindly.

Jim said...

Anon 8.05

Your first point: How pedantic do you want to be? The ISID/IJID is/are presumably very reputable society/journal respectively, and would not publish something which had not been peer-reviewed. What are you trying to say about the authors of the report in question?

You say "both sets of results could be correct - for the time period to which they relate." The point surely is that a bTB outbreak does not compartmentalise itself neatly into boxes according to arbitrary time periods decided by us, Bourne and post-Bourne. One is looking for trends over time, and the paper in the IJID appears to suggest something interesting where Bourne's edge effect is concerned (albeit, as George has said, predictable in light of Thornbury).

And, no, I haven't read the IJID paper yet. I've tried to get hold of a copy, but so far it seems to be available only to paid-up subscribers. I fail to see what is wrong in reporting what someone else (who has read the report) has said about it. The context is perfectly clear from the original posting. If you could point us in the direction of the report, please do so.

Matthew said...

Anon 8.05.
We said, quite clearly I think, that the story had been sourced from one of 2 or 3 farming publications which carried it last week. We now have the benefit of sight of that paper and can answer your questions.

Elsevier - a subscription site - has it on web link and state they publishing on behalf of the International Society for Infectious Diseases. It will be published in the society journal, the International Journal of Infectious Diseases. We are unable to provide you with a copy. Although from your comments I suspect that you may have one.

The lead author is to be cited as 'Jenkins, HE et al. The et al being Rosie Woodroffe and Christl Donnelly - late of ISG fame.

The paper looked at the trial data for each of the years in which it tried to cull badgers, and then ran the data onwards for a further two years at Defra's request and cost.

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.

Conversley 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 scrape up.
But within two years, that negative effect had somersualted to a (minus) -30.1 percent incidence outside the proactive zones.

The summary results:
"During the post trial period, cattle TB inside culled areas was reduced, to an extent significantly greater than during culling. In neighbouring areas, elevated risks observed during culling were not observed post trial.

And concludes:
Although to-date the overall benefits of culling remain modest, they were greater than was apparent during the culling period alone. Continued monitoring will demonstrate how long beneficial effects last, indicating the overall capacity of such culling to to reduce cattle TB incidence.

Anonymous said...

Thank you Matthew 10.04pm. That's a much better description of the paper. I hope you agree with me that the others were not exactly others as they were former members of the ISG. And, now you quote more fully from the paper, we can see that it doesn't disagree with the ISG final report but adds to it, in terms of a more complete picture with the added benefit of the extra time. I think Figure 1 is particularly interesting as it shows, what looks like, a trend over time (as you describe).

I'm neither for nor against badger culling, I just object to things being misreported and you made it sound as though different people had reanalysed the RBCT data and come up with a different result which is not the case at all. But thank you for making it clearer to readers.

It will be interesting to see if there are more results over the next year or two and at what stage things go back to "normal".

Matthew said...

Anon 10.45

We also note that much of the references to 'culling' is followed by the bracketed proviso (as conducted in the RBCT) - which supports / mirrors Bourne's words to EFRAcom last year. The implication being that anything other than an 8 night annual hit-and-run using cage traps, may have had a different outcome.

We note [362] "growth of the badger population would be expected to increase the risks of cattle becoming infected from badgers" and [364] "reduction in badger mobility would reduce those risks"

The authors with their electrical abacuses (abacii?) appear to have reached a similar conclusion to that of state vets and farmers?

Badgers do transmit TB to cattle with levels of infection proportional to the size of the infected badger population and any 'movement' between groups. Thus any cull of endemically infected badgers must minimise perturbation opportunities and the fracturing of social groups which leads to territorial scrapping and spreads the disease wider.

That is not to say things can be left to fulminate.

Clean Ring badger culls practised in response to confirmed outbreaks of TB not associated with bought in cattle, did this on a smaller scale, gassing and then trapping (which proved less successful and more had more interference). Culls lasted for up to 6 weeks in a very tight area, only stopping when tested badgers / cattle were found to be clear of TB. Thornbury gassed a larger area and in places this persisted for 8 months; both culls drawing in dispersers from other groups seeking to fill the vaccuum left.

The 'beneficial effect' - not modelled, but actually seen - was anywhere between 5 - 20 years (personal experience + vet info) for small scale clearances, and a documented 10 years plus for Thornbury. Badger numbers recovered to pre cull levels over time.

As seen by the horrendous herd breakdown figures, cattle slaughterings and spill over of a grade 3 pathogen into other mammalian species, walking away from this is not an option.