Friday, December 11, 2009

Definition - 'Maintenance'.

It has become apparent over recent months that a great many misconceptions - some originating in the top echelons of Defra - have been dribbled out to a gullible audience, unchallenged. The description 'maintenance' reservoir for instance, appears to have been atttached umbilically both to badgers as a source of bTB - and also cattle in equal measure. This is not so.

A dictionary definition of the word is 'capable of maintaining', 'cause to continue', 'retain in being' and 'preserve intact'. You get the picture? Badgers (unfortunately for them) tick all the boxes which allow this very accurate description to be applied.

Research over many years has found that they can maintain body weight, bear and rear young, in fact survive quite happily, while intermittantly shedding bTB. In the latter stages of the disease, the body is overwhelmed by disease and they are excluded from their groups, ranging further, scrapping and fighting for territory, and hiding up in shallow, single hole setts, often close to farm buildings and an easy food supply.

At this stage and possibly before, depending on the site of lesions, their ability to transmit disease is phenomenal, with up to 300,000 units of bacteria available in just 1ml of urine. 30 ml is dribbled at each void or used for scent marking, and just 70 units is needed to infect any cow who sniffs it. And while cattle will usually avoid faecal contamination, there is less chance for them to avoid urine. Pus dropping from open abcesses (see pic.) is also an opportunity for disease transmission. The amount of bacteria in badger lesions is huge.(All this is archived in the PQs which form the base of this site.)

So what of cattle? If they are left untested, and fulminating disease, then of course any TB would spread. And in the 1930s and 40s it did. But after the TB eradication process in the 1950s and 60s, using test and slaughter, this country - like many others - had all but eradicated TB. Numbers of reactors dropped to a very low level, with just an isolated animal expected to turn up at slaughter with aged, walled up lesions. The exceptions were two 'hotspots'. One in Glos and the other in SW Cornwall where test / slaughter failed to clear the problem - even with whole herd slaughter, cohort slaughter and all the rest of the cattle-only-tools. We explained this in our posting here - a posting which was compiled for us, by Divisional Veterinary Managers who had overseen this eradication process.

Cattle lesions are not particularly laden with bacteria, in fact scientists have explained to us that they "could look for half an hour" before finding a single bacteria on culture slides. Conversely the pink stained badger excretions "were jumping off the slide" and visible without the need of a microscope. Thus in the field, cattle to cattle transmission is difficult and happens over a long time scale. A fact born out by the Pathman project which found no samples taken from salami sliced reactor cattle over a long time frame, to be capable of onwards transmission.

So we go back to our Parliamentary Questions - and more particularly their Answers, where on 30th January 2004, Col 540W [150492] baby-Ben Bradshaw replied:
"All countries that have either eradicated or have a programme to control, bovine tuberculosis use one or more forms of the skin test"

of which the 'comparable intradermal' version is used in the UK, and its efficacy?:
28th January 2004 Col 382W [150495] "... on standard interpretation, provides sensitivety between in the range 68 to 95 per cent and specificity in the range 96 - 99 per cent."
Thus on regularly tested herds (and ours has had 60 day tests for way too long) - the top end of 90 per cent is as good as it gets. The junior Minister also mentioned that "In the abscence of a wild life reservoir ", all countries operating this test and slaughter policy had eradicated or were a way down the road to eradicating bTB completely. How would that be possible, if cattle were indeed a 'maintenance reservoir' of this disease? Or is our UK bTB bacteria different from anywhere else in the world? (We are aware it has acquired a 'political' DNA appendage - but let that pass....)

The Minister also told us that after the badger clearance at Thornbury, and smaller trials in Steeple Lees, Hartland and East Offaly, cattle TB had reduced significantly or in the case of Thornbury - disappeared altogther for at least ten years, with 'no other contemporaneous action' involved, other a clearance of infected badgers. How could that be, if cattle were 'maintaining the disease?

In a regularly tested cattle population, with reactors removed promptly, cattle do not 'maintain' TB. And when the unfettered, free ranging 'maintenance' reservoir of infection is controlled or removed, TB disappears from cattle populations completely. Once again we are grateful, for permission to reproduce the chart below, painstakingly compiled by AHOs in the SW, showing their professional risk assessments for cattle breakdowns. And as you can see - cattle are not the problem. The vast majority of cattle breakdowns were attributed to badgers.


The description 'maintenance' when applied to cattle TB, is not born out by past experiences both in this country or more especially in others where no wildlife reservoir exists, (or if it does present problems, it is controlled in parallel).

Thus, in our opinion, it is at best misleading and at worst duplicitous to describe cattle as a 'maintenance reservoir' of bTB - unless of course that description refers to the largesse associated with pensions and employment generated by its continued and increasing presence.

3 comments:

Sharon said...

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Anonymous said...

You forgot to mention the work of Green et al.: "Estimates for local and movement-based transmission of bovine tuberculosis in British cattle" (Proceedings of the Royal Society B, January 2008)which attributed just 16% of bTB outbreaks directly to cattle movements, and concludes that "high risk [bTB] spread is probably the result of cattle and badger interaction"

Matthew said...

Anon 5.08

Thanks for the reminder.