Saturday, November 21, 2009

Alpacas - TB inter herd spread.

It was only a matter of time before 'bovine' TB, now entrenched in a well protected but exploding population of badgers, spilled into non-bovine species. And if our Minister for (some) Animals' Health does not turn a hair at the slaughter of thousands of cattle annually, he may just have a fight on his hands with owners of some extremely highly valued alpacas, which when they do contract TB, appear to be more than capable of spreading it between themselves.

We have returned to this subject several times since the first alert in November 2007, after a west country llama farm was decimated by disease. The case was later described in the Veterinary Record, from which we quoted in this posting. Today we received data from another alpaca stud, with a similar story to that of the Devon breeder whose females returned from stud in Sussex, carrying a Shropshire strain of TB, from which they subsequently died.

A Gloucestershire breeder has sent us the following snapshot of his experiences. His story started in early September, after visiting shows with 3 young stud males during the summer. No other disease problems were found throughout intense veterinary investigation; but within a week, three of these animals were having breathing difficulties and had measurable weight loss. Wide spectrum antibiotics failed to give results. By mid September the first casualty was euthanased and his post mortem revealed lesions on lungs and liver. Two weeks later, a second alpaca died with similar post mortem results and the third was euthanased, again with the same pm results.

The owner takes up the story:
My spoligotype has been confirmed as type 10. My Defra veterinary officer has confirmed that there have been no type 10 outbreaks near to me, which confirms their and Animal Health's initial suspicions that my herd had contracted this disease at a show. All of the three initial cases were in my junior male show team.
But as has become apparent with other cases of alpacas with bTB, inter-herd spread, often before owners have a clue what is going on, had already begun:
We lost a 40 month adult female recently (she had been in the paddock alongside the junior males for some months. As is the way with these things, she is also a show winning alpaca). I currently have three others in isolation. Two other junior males and the 12 week old cria of the dead female.
The veterinary attention these animals have been offered (banned in the case of cattle) extends to specific anti-tuberculosis drugs, used in the treatment of humans:

One of the boys appears to have responded well to Isoniazid (anti-tuberculin drug) and is back to normal weight and breathing normally. Balthazar, a multi show winning grey male, is the most recent to go into isolation and is now on Isoniazid. The drug isn't cheap but, since I was offered £8,000 for him I'm not giving up - apart from the value, I had hoped to keep him as a member of my stud team. Oriel, the cria, seems okay at the moment but, as his mother died of bTB there's a reasonable chance he could get it.

Alpaca owners have lobbed a string of correspondence in the direction of Defra's window-box over their problems with camelids. And the frustration of owners of animals infected with this devastating disease when they are met with little advice, no support and condescending pre-programmed platitudes, only increases their anger.

Like the Devon animals, (who contracted Shropshire strain 35 TB from a visiting female while in Sussex), this alpaca owner has delved into the source of his outbreak. As he points out, no alpaca has presented to VLA at this time, exhibiting Type 10 bTB. This is unlike the Devon case, where although the Shropshire female died at stud, another animal from the Shropshire farm did subsequently come within Defra's radar. He explains:
Some alpaca studs have dozens of these visiting females - so you can see the potential for spreading bTB and other diseases/parasites to the four corners of the country. As far as I have been able to find out, there is no other alpaca stud/farm with spoligotype 10 known to Defra. This makes one think that there has to be someone out there that has had animals die but, has not had any post-mortemed. Given the attitude of some of the larger commercial breeders to the bTB issue and to those of us that are making a "fuss", they probably don't want to find out as it would be too damaging to their businesses. However, if left to fester, none of them (whether currently infected herds or not) will have a business left within a couple of years.
Quite. TB in camelids is a killer, and although the intradermal skin test is regarded as the primary test for camelids, even on the recommended 'severe' interpretation, it is not doing the job. Figures of less than 20% accuracy have been bandied about and a member of the BAS board has told members that only 6 alpacas have tested positive using it. This although members of the society themselves can account for in excess of 100 animals dead from TB in the last few months.

The blood test has been flagged up as a possible ancillary ante mortem test, but veterinary practitioners experienced in the care and treatment of these animals say that interpretation of the test is not solid enough. This alpaca owner has been told that
" the only way I can be sure that my herd is free of bTB is to use the blood test, but I should be prepared to lose 4 or 5 healthy animals for every one that is genuinely infected."

He concludes: "For obvious reasons, this cannot be regarded as a satisfactory solution - especially as the Government will only pay £750 per alpaca (if they pay at all)".

This is a very sobering tale, running parallel to the experiences of many other camelid breeders across the country, and beyond. If Defra continue to bury their heads in the sand, this country runs a very real risk of establishing a second, unchecked reservoir of disease - if it hasn't done so already.

Accurate testing for any disease is vital. And if the skin test is failing camelids, and blood tests are failing them as well, why not dredge up Defra's most unfavourite toy, now widely used in the diagnostics of many other diseases in most countries - except TB in the UK of course; PCR? Just a thought....

Our grateful thanks to the owners of these beautiful animals for sharing their story - so far.....


Anonymous said...

A very interesting posting that clearly points out the risks of moving animals around the country for various reasons.

Would PCR really be the magic bullet?

Can you point us to some facts regarding PCR's accuracy and practicality in diagnosing bTB please?

One has to wonder if the alpaca scenario doesn't sound just like the cattle situation in miniature, and one could argue 'till the cows come home' on how to eliminate the disease causing bacterium from the planet.

Chris said...

You're right that testing is critical, perhaps more so with BTB than any other animal disease at the moment.

However, PCR isn't the answer. The first issue is what sample do you use for your PCR test? The most commonly available samples are:

* Urine - should be sterile and there has never been any evidence for excretion of mycobacteria in urine

* Faeces - there is some contradictory evidence of mycobacterial cells in certain species but you would have great difficulty with sample prep and tracing

* Blood - haematogenous spread of mycobacteria is possible but extremely rare. When it is found it is usually at a very late stage of disease progression and very rarely seen in the UK cattle population.

Testing would be improved greatly by implementing better control and further development of the skin and IFNg tests. However, testing is useless if the animals are left on the farm. Anecdotal evidence suggests that reactor cattle have been left on farms for in excess of 6 months post disclosing skin test.

It doesn't matter how good your test is if you can't implement policy and do something about infected animals.

Matthew said...

Anon.@ 9.42
We are sure that in time PCR technology will be adopted for faster and more accurate diagnosis of many diseases. It is already used in hospitals for human bacterial screens, and in other parts of the world in numerous animal diseases.
(It was offered to Defra,[then called MAFF] in 2001 by the late Fred Brown, of Plumb Island research facility in the USA, who had successfully trialled it in the field for FMD.
MAFF / Defra turned it down, preferring to slaughter 11 million animals.)

The successor at Plumb Island is Dr. Roger Breeze, who is using this stunning technology across the world, mainly in Eastern Europe.
Michigan pioneered its use in the States almost a decade ago, for bTB in cattle lesions (saved time of growing cultures)
Warwick University had good results using it in environmental material from badger setts in 2006.

It is now in regular use for some cattle diseases, but Defra (and Warwick) hold the assay needed to fuel the thing for bTB, thus its progress and 'validation' is entirely in their hands.

Chris. @ 11.25

Not sure why you are against PCR?
You ask what sample to use for bTB.
Samples which contain, or are likely to contain the bacterium ?

In alpaca, possibly sputum samples, as many appear to have extensive and open lung lesions.

In badgers, urine / sputum / pus have proved adequate from latrines and bedding if not the animal itself. (Urine from badgers can be extremely heavily contaminated with up to 300,000 units of bacteria in just 1ml urine.)

PCR is now being used on faecal samples from cattle, to isolate Johnnes disease - notoriously difficult, and a member of the m.avium paratuberculosis family.

There is a huge difference in infectivity of bTB in different species, with cattle being pretty non infectious (see Pathogenisis Project, where over 1600 samples from reactor and contact cattle proved negative for culture and onwards transmission of disease. Even from 23 with lung lesions.). Reactor cattle may have lesions but exhibit very few colony forming bacteria, and thus are not so capable of onward transmission. The exception to that is long term open lung lesions, or udder lesions with milk fed to calves.

Conversely the amount of bacteria in even small badger lesions is huge, and onward transmission readily occurs, both between badgers and to any other mammal.

From what we have gleaned, alpacas appear to exhibit the worst of both these ends of the spectrum. They are very susceptible to bTB bacteria, which rather than walling up, develop very quickly into full blown infectivity. And they have proved more than capable of onwards transmission within their herd - or punta.

While badgers can wall up their lesions, shedding intermittantly for up to 8 years, alpaca seem to overwhelmed by this insidious disease with months.

As we have said many times, the intradermal, universally used skin test for cattle is fine. It works. But leaving a festering wildlife reservoir to spill back into those sentinel tested cattle is shortsighted nonsense.

We are told that the skin test works in caprines (goats) but it is apparent from both the veterinary press and personal communications, that it is failing in camelids.
It doesn't work in badgers either.

Blood tests too are far from secure, with gammaIFN hoovering up far too many positives to numerous other bacterium than m. bovis in cattle. And the Rapid StatPac blood test proving equally unreliable in camelids, with both false positives and false negatives. This may be down to too rigid an interpretation of it. And on that, we are not qualified to comment.
The live test using bloods from badgers was also abandoned because of a dangerously low 47 percent sensitivity rating on a negative reading, although on positives it was much better.

Chris said...


"Blood tests too are far from secure, with gammaIFN hoovering up far too many positives to numerous other bacterium than m. bovis in cattle."
Can you cite your evidence on that?

To clarify, I'm not anti-PCR at all. As far as I am aware, the problem with the Warwick PCR was that it was generating a lot of false positives. There was anecdotal evidence that an M. avium control showed up as M. bovis.

Perhaps I should have been more clear. I was talking specifically about the disease in cattle, where there is little evidence of haematogenous spread, excretion in urine or mucosal samples.

You're right about the skin test not working very well in camelids or mustelids. Sadly we aren't likely to see much in the way of development in this area at the moment as there isn't the impetus to develop tests for the "relatively few" camelids out there.

On a personal note, I wouldn't trust any of the serological tests as far as I could throw them. Given the route of pathogenesis of M. bovis you're unlikely to generate an easily (and cheaply) detectable humoral immune response.

Matthew said...

Chris @ 5.11

Agree on the relative non-infectivety of bTB in cattle.

You ask about our sources for the comments on gammaIFN.
Two years ago, one of our contributers had a gammaIFN positive animal, so asked a few pointed questions about Defra's new toy.

The pilot study was conducted under a very strange set of circumstances, in that it was slipped under the radar of other bloods, and thus could not slaughter positives to confirm disease - or not. It was trialled in the areas where Defra did not expect to even find positives, so it was a shock to get any. And they did get some. So, these herds were 'excluded from the trial'. And gammaIFN was launched.

On further detailed examination, some of the herds showed heavy concentration of m.kansassii and others may (according to Governement Veterinary Journals and other publications, and our own experiences) have been exposed to Johnnes (m.avium paratuberculosis) or the quite harmless 'skin' TB.

Although cited as detecting bTB antibodies more quickly than the skin test, that is a matter of days not months, with gIFN able to detect exposure to infection after 21 - 28 days, and the skin test after 30 - 50 days.

The number of skin test positive cattle proving NVL at slaughter is approx 50 per cent, with even the Pathogenisis salami sliced candidates, achieving 48 per cent NVL, compared with local AHO postmortems 51 percent.

An answer under F of I revealed that "demonstrable evidence of TB [i.e lesions or culture] is typically found in 18.6 percent of gIFN reactors".
So quite a difference.

Re. Warwick. We were unaware that Warwick's trial in 2006 was able to cull the badgers from positive setts, to prove their PCR diagnosis?

We understand that there were about 30,000 camelids at the last count, but here the problem is that these delightful creatures appear to have the power to become 'super excreters' very quickly, and very often. And that poses a huge onwards transmission opportunity, both for the rest of the group, wildlife and the human beings and veterinarians attending them.

We personally have no problem with the skin test, which, combined with slaughter of reactors, has cleared tb very successfully, and completely in countries which do not the a wildlife reservoir of the disease.

Uniquely, the UK appears to think by culling the sentinel messengers, the tide of TB will turn, even if it leaves a wildlife reservoir to fester.

Canute found that was not the case.

Anonymous said...

Until a reliable method of diagnosis is available the Camelid industry should self regulate. Movement records should be mandatory and maintained by BAS for all to see. I am shocked that Futurity is going ahead at Stoneleigh - an area currently free from TB.

Anonymous said...

British Alpaca Futurity 2010

2010 Futurity will again take place at the National Agricultural Centre at Stoneleigh Park on the 26th and 27th of February.

An opportunity to spread the disease or to test all the premier beasts for bTB both on the way in and on the way out?

Come on! You know it makes sense !