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Email received January 7 2010 from Dr Colin Fink,
There is a problem with badgers highlighted to me by Professor Liz Wellington at Warwick, whose team have done the surveillance work. Evidently there will be a few badgers who are the high excreters of Mycobacterium bovis. They are ill and often excluded from the setts. The question which is difficult to answer is how many unaffected badgers are carrying the bacterium? They may remain healthy and not excrete particularly. We could decide to eliminate whole sett populations. If we do we would have to destroy and disinfect the setts as they will be re-colonised by other individuals and the Mycobacteria will still be there to infect the new population.(Dr Colin Fink is Clinical Virologist & Hon. Senior Lecturer in Biological Sciences University of Warwick, and Company Medical Director, Micropathology Ltd Research and Diagnosis)
It may be possible to both undertake sett elimination if the evidence of infection is available, and also treat geographically around the sett with triple antibiotic loaded bait (repeatedly). So those locally will at least have any infection reduced and carriage eliminated. It may also be possible to bait with contraceptive hormones so populations also naturally decline.
I do not think that any single policy is a panacea and we need to consider combined approaches, to reduce the carriage and excretion of organisms, minimise population pertubation, which creates stress and increases mycobacterial disease ( rather than carriage), by using selective sett culling and also consider in conjunction, both contraception and antibiotic baiting.
Any combined approach will need very careful policing and implementation. Surely that is a better investment than constantly killing herds of cattle and all that which goes into raising these animals?
We have no other alternative as vaccines are not available because the organism is not amenable, and we are losing herds of cattle, alpacas etc and increasing the organism load in the wild population at an alarming rate.
(See also the exchange of views, in September 2009 on the subject of risk to human beings as well as the toll on cows and other mammals between Dr Fink and the farmer, Pat Bird, author of the Bovine TB Blogspot) With their permission, what follows are some of the current thoughts of Dr Colin Fink (in black) and the farmer, Pat Bird (in blue) on the subject of bovine TB
From emails sent to warmwell.com Sept 21 2009 (On suspected human cases)
I read your bovinetb.blogspot reference with interest. M.Bovis is regarded as a zoonoses, of course there are well documented cases of it transferring to man. In the case of the cat diagnosed to have the disease, if the owners and immediate family remain asymptomatic, then all is well . Whether they have been exposed and have been infected with a small amount of the organisms and deal with this infection in the normal immunological way, is rather academic. Many of us meet M.Tuberculosis but remain entirely asymptomatic. The cat owners et al may be reassured. If they were to become ill and remain unwell for longer than a transient infection might be expected to last, then further investigation would be justified. As it happens we are able, and do, diagnose Mycobacteria of all sorts- there are many different types. ( we look for the Mycobacterial DNA and then sequence it to characterise the species of Mycobacteria). But no intrusive investigation ( biopsy of lymph nodes, lung biopsies etc) to find the organism, can be medically justified in someone who is entirely well. - It would be a hazardous undertaking.
22 September 2009 00:11
The real problem is that the organism hides, so unless there is an obvious focus for infection for example, a swollen knee or coughing rusty sputum or an eye with uveitis ( pain and loss of vision) you just do not know whether someone is infected.
You see the skin test is just as useless in us as it is in cattle. It will show that we have mounted a T cell response, so have met the organism ( I am not sure whether the skin test is Mycobacterial species specific: I suspect not) but so what? We have met some of the organisms and raised an immune response. That does not mean we are rampantly infected.
Tuesday, September 22, 2009 11:55 PM (From Pat Bird)
Agree with much of what Dr Fink says, except this:
"...the skin test is just as useless in us as it is in cattle. It will show that we have mounted a T cell response, so have met the organism ( I am not sure whether the skin test is Mycobacterial species specific: I suspect not) but so what? We have met some of the organisms and raised an immune response. That does not mean we are rampantly infected."
Yes and no. The intradermal skin test is the primary universal test for TB in cattle, and with that + slaughter most countries have cleared the disease altogether. The cattle skin test is 'comparative' in UK, as it compares a bovine TB antigen based on AN5 strain, to an avian TB antigen reaction, and records if the animal has mounted an immune response to either, and if so, the difference between the two. The only loopholes in its use are a latency 30/50 days prior to the skin test, or if the animal cannot mount an 'immune' response as it already has the disease. It is then said to be 'anergic'. I have endured years of consecutive 60 day skin tests - or our cattle have - and it does what it says on the tin.
Dr. Fink is quite correct to say, the test does not show that any candidate testing positve is 'rampantly infected'. In the case of cattle, they get no chance - they are shot. In human beings, the first line after contact with either a human case, or animal (farmed or domestic) should be a Mantoux test to detect if exposure has occurred. Which if it is positive, would certainly not mean invasive biopsies.
Records of recent cases describe bloods and PCR to see if sputum was ++ for bTB, together with Xrays. After which, a long course of appropriate antibiotics, if no evidence of operable lesions is detected . The Spanish couple with the alpacas are on a course of prophylactic antibiotics as the infection in their animals is so widespread.
It came as quite a shock to local AHO staff and vets that one of their colleagues contracted bTB via an alpaca postmortem conducted on farm. She developed bTB in the bone of her thumb, which required deep bone scrapes, reconstructive surgery and the inevitable antibiotics. A Cornish woman and her daughter both had clinical bTB and her dog is dead. The mother had lung lesions, the daughter was sputum positive. The dog extensive lesions in many places after selective euthanasia. All had the same 'spoligotype' of bTB that is circulating in tested slaughtered cattle, and the free ranging badgers 'known to inhabit her garden', one of which she 'rescued. She had not worked as veterinary nurse for three years before she became ill.
The amount of cattle we're killing due to 'exposure' to m.bovis in their environment, should be ringing warning bells that the amount of m.bovis is increasing. And it available to any mammal who cares to trip over it.
Any country which ignores a reservoir of bTB as we are doing (in wildlife) , is storing up problems for its human population in the future, and for just the reason Dr. Fink gave. It can wall-up and lurk deep within the body, until the immune system breaks down, when it will release, often decades after exposure. And that is precisely why it is a listed as grade 3 pathogen.
And HPA are not fulfilling their statutory duty if they fail to 'screen' contacts of anything positively confirmed. Particularly children whose immune systems are not fully developed.. (All in my opinion of course.)
September 23, 2009 10:17 AM - From Dr Fink
A very good discourse with much more detail than I gave. I would question one thing: a positive mantoux ( skin test with old tuberculin - a protein from the organism) can show previous exposure. Whether that is recent exposure to a suspected animal infection and thus infection or coincidental from a previous exposure is a bit harder to fathom.
Of course the cattle are not given the benefit of the doubt with a positive skin test. Only very modest numbers on post mortem are found to have lesions.
In my experience looking for any Mycobactarium in the blood ( by PCR ) even in broken down cattle - I had the opportunity with DEFRA a few years back, will not show organisms, so one may be falsely reassured. Sputum testing may show either miliary ( widespread infection ) or a more localised lung infection. But not always. Biology and organisms never do what they are told to in the text book.
The real problem as Pat says, is that there is far too much out there and we need to reduce the load in the animal reservoirs in a humane and satisfactory way. The trouble is we do not have a decent answer to that problem and any attempt will be messy, gird up the badger lovers ( understandably) and may not do the job very well.
I am still of the opinion that feeding stations with high dosage of triple antibiotics for say 6 months coordinated, could be worth a try. It would not be that expensive, but would need very good attention to detail. It would at least reduced the bacterial load in those wild animals that are a reservoir for infection and often excluded from the badger setts.