Thursday, November 22, 2012

Field based tests for bTB

As we continue to stitch together a workable alternative to the now postponed Son-of- RBCT shooting parties, a solid and reliable field test for m.bovis in the field is a priority. Thus far, we would propose the following:

 Firstly, use AHVLA risk assessment TB99 reactor locations to map problems over a wide area. These are already done, thus incurring no extra cost - but they lie gathering dust, as they did in the RBCT. And any reactor would suffice - there are enough varieties now to choose from. Take your pick.

Secondly a farmer / Wildlife Unit trace to overlay a wildlife interface map with such reactor locations could involve farmer participation, thus reducing costs again.

 Thirdly the location of any wildlife sharing the location of reactors identified by steps 1 and 2, would benefit from a 'scientific' thumbs up. But that has to be through true 'science'. Not the smoke and mirrors of a simple mathematical model based on vague assumptions, which like the Emperor's new clothes, none but a very few dare question.

 And while the now validated PCR test is our favourite as a sett based screen, a close second could be an American ELISA antibody test which, it's manufacturers tell us, has gained OIE approval, and can give a result in the field in 3 hours. Although primarily their predicted use is cattle based, one assumes (perhaps wrongly ?) that this test would work for badgers too.

And another field based test is described by the University of Tennessee research team as 'giving results in 5 minutes'. It is said to work on defining markers in body fluids such as blood, milk, saliva or tears - which sounds suspiciously like PCR to us. They describe the kit thus:
With this device the incubation time is significantly reduced when compared with conventional immunoassay methods (e.g. ELISA tests) and experimental data shows the device takes less than 5 minutes to differentiate disease-positive samples from negative samples. The device does not require direct/indirect labeling of the analyte (antibody, biomarkers) and can be used with any combination of probes (e.g. antigen) and analytes (e.g. serum antibody).

The one-step method is not labor intensive, does not require a specialist to run the test and ensures consistency in results. Also, because of the small size and of the automated one-step method, the system allows on-site (bed-side, in-field) diagnosis of pathological and physiological conditions, reducing time and costs associated with remote testing in diagnostic laboratory. This device has been tested on Johne’s disease and bovine tuberculosis, and the results show a higher accuracy than currently-available diagnostic immunoassays."
UPDATE: Link added with more detail on the University of Tennessee's field based test, which they confirm would cost around $500 for the kit, with each screen (chip) costing $1.
The manufacturers of at least one of these in field tests also confirm that they are working with FERA on field trials for the product.

 The ISG mentioned an ELISA test in their Final Report - then damning it's low sensitivity:
1.7 [] ... A live test for badgers had been developed and subject to trial from 1994-96, but its sensitivity was much poorer than had been hoped, successfully detecting only about 40% of infected badgers (Clifton-Hadley et al., 1995-and Woodroffe et al., 1999)
We have no details on the sensitivity of IDEXX's blood assay, but it is to be hoped that it may be an improvement on the old 'Brock' test, as well as being faster and field based. And of course that they are able to cage trap more than a few wild badgers on which to use it. We say this guardedly having listened to a prominent farmer trialling vaccination, and describing efforts to capture his sett occupants, which resulted in just one being trapped in an operation lasting  several weeks.

It may be also prudent to point out that the Wildlife Unit personal, trying to sign up farmers for the RBCT, tell us that over half in some areas refused to take part, when they heard that healthy badgers were to be culled as well as diseased. And the badger 'Live Test Trial' ( 1994-96) experienced no problems at all as only diseased badgers were targeted.

 It is our understanding that the direct target of a positively identified reservoir of a zoonotic pathogen trumps any more emotive considerations for the continued survival of that reservoir. And once identified, should it be left to upspill disease into other mammals, then litigation is a distinct possibility. Which the cynical amongst us would say is possibly enough reason for the current political block wall against such targeted identification.

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