Monday, September 05, 2011

Update on PCR technology

We have explored PCR (Polymerase Chain Reaction) technology in many previous postings. But it appears that some readers and the wider industry are falling behind in just how far these diagnostics have advanced in a few short years.

In 2003, the most usual 'primer' used for PCR was m.tuberculosis complex, an overall grouping of many bacteria, sharing some of the same genetic material. Thus the results were similar to putting lawn mower petrol in a Ferrari. It coughed and spluttered and only achieved an 86 per cent sensitivity. Compared to gammaIFN, that could be considered good - but let that pass.

Move on a few years and last week the International Society for Infectious Diseases, ProMed, reported the findings based on pathology and histology of another dead alpaca. First published in the Veterinary Record, ProMed describes the methodology of 'spoligotyping' to establish strain types of m.bovis, using PCR thus:
Spoligotyping (spacer oligonucleotide typing), a polymerase chain
reaction-based amplification of a region of the mycobacterial genome, is recognised as a rapid and reliable test for the differentiation between _M. bovis_ and other mycobacteria.

".. recognised as a rapid and reliable test, for the differentiation between m.bovis and other mycobacteria. So by amplifying part of the genome, unique to m.bovis it would appear that the Ferrari may function to expectations ?

Thus we offer our continued support to the Alpaca TB Support group for commissioning their Proof of Concept project. If this study can demonstrate that PCR technology, already widely used in VLA for other diseases including Johnnes (m.avium paratuberculosis), is useful in the diagnosis of bTB, then there is every likelihood of its being used for other species, especially cattle. For instance, PCR could avoid the long wait, sometimes of weeks, while bacterial culture is carried out to confirm that a suspected abattoir case showing visible lesions is, in fact bTB.

PCR technology detects m.bovis the bacteria: it is not fussy as to its host. So other species which vets are finding difficult to diagnose with the intradermal skin test (such as pigs), may also benefit. And ultimately, operating in 'real time' and not laboratory based, the technique may prove a vital tool in locating 'environmental' TB spilling back into domesticated species.

As an additional tool in the eradication of bTB, PCR could be extremely useful, plugging a gap in our current tests. Although commissioned and paid for by a small group of camelid owners and others, bTB (m.bovis) in camelids should not be seen in isolation from the disease in cattle or any other mammal, since the same bacteria is responsible.

Please note that any donations to this project should be made direct to the AlpacaTB Support Group who can be found on this link. For more information, see the PCR tab on the top bar, and how to contribute on the 'Donate' button.

This is bTB in an alpaca. And it is not pretty. This animal's lymphatic systemic was bursting with solid cheesy abscesses of bTB, his liver is spotted with abscesses and he was infectious with every breath he took, due to open lesions along his trachea, right up to his throat.

Now whether they are still regurgitating out of date research into PCR technology, or whether it is not in the interests of the wider alpaca sellers to confront the problem of bTB is debatable. But thus far we see no reference to this project on their websites, and certainly no information as to how camelid owners may support it, should they choose to do so.
And we are puzzled as to why this should be so.

But being a magnanimous lot at blogger HQ, we expect the main Societies representing camelid owners are waiting to contribute to some further validation projects for PCR, which could bear their unique names and affiliations.

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