TB Gamma Interferon Tests Help and advice please

[An Gof]

I'm looking for some help and advice on Gammons Interferon tests for TB. Maybe @matthew can help.
I had an animal go down in the abattoir with suspected lesions that, after culture, proved positive. This was a surprise as we have been TB free for 8 years or more.
We had a full herd check test and passed as fully clear. Last week we had our first short interval test at severe interpretation and also had to undergo a gamma interferon test. The skin test was again all clear but i have had notice from APHA that two animals are reactors to the gamma interferon test. What surprises me is that both animals are young, 8 month old intensive steers that have been housed since coming onto the farm and have never spent a day outside.
Just how reliable is this gamma interferon test? If the +ve's had been from animals that had been out grazing all summer i would have been disappointed but not surprised. But young, intensive animals that have been housed all their life? Seems strange and surprising to me. Also a large number of resamples to do.

I would be very interested in other peoples comments and experience.

TIA

 

[tinsheet]

I'm looking for some help and advice on Gammons Interferon tests for TB. Maybe @matthew can help.
I had an animal go down in the abattoir with suspected lesions that, after culture, proved positive. This was a surprise as we have been TB free for 8 years or more.
We had a full herd check test and passed as fully clear. Last week we had our first short interval test at severe interpretation and also had to undergo a gamma interferon test. The skin test was again all clear but i have had notice from APHA that two animals are reactors to the gamma interferon test. What surprises me is that both animals are young, 8 month old intensive steers that have been housed since coming onto the farm and have never spent a day outside.
Just how reliable is this gamma interferon test? If the +ve's had been from animals that had been out grazing all summer i would have been disappointed but not surprised. But young, intensive animals that have been housed all their life? Seems strange and surprising to me. Also a large number of resamples to do.

I would be very interested in other peoples comments and experience.

TIA

Lost 7 incalf heifers (20 months) last winter to the gamma test! All clear in the abattoir, ministry vet said it just shows they've been exposed to Tb.
It ended up being called a clear test to top it all off!!
had 6 re samples to do also.
No it's not reliable, any more so than the skin test, (in my eyes)
Sorry not much help, but there never is were tb's concerned.

 

[puntabrava]

Strange they went straight to GI test when you have been tb free for 8 years, normally they will only do it if you have been shut down for a few years.

 

[An Gof]

Strange they went straight to GI test when you have been tb free for 8 years, normally they will only do it if you have been shut down for a few years.

Apparently the reason for having to have the Gamma test was that we are in a Cull area and have just completed third year of it.

 

[puntabrava]

Apparently the reason for having to have the Gamma test was that we are in a Cull area and have just completed third year of it.

So are we in this part of Wiltshire but they are not using GI relative to your situation.

 

[bean]

Think as soon as you get lesions in cull area they do gamma test.

 

[epfarms]

The skin test is not that sensitive, but very specific. This means if there’s 1000 truly infected animals, this test will only “find” about 700-800 of them. If, however 1000 truly un-infected are skin tested, it will only accidentally find one positive.

The GI test is somewhat the opposite, much more sensitive, less specific. So of the 1000 infected animals, it will find far more of them, we’ll over 900. The down side to this is a lack of specificity, in 1000 in-infected animals it’ll accidentally find about 50 false positives.

They like to use the skin as an initial screen because you’re unlikely to find false positives. If they suspect/know you have TB in the herd, they’ll use GI as it’s far more likely to find all your infected animals and clean up your herd, at the expense of 5% innocent bystanders unfortunately.

 

[matthew]

I'm looking for some help and advice on Gammons Interferon tests for TB. Maybe @matthew can help.
I had an animal go down in the abattoir with suspected lesions that, after culture, proved positive. This was a surprise as we have been TB free for 8 years or more.
We had a full herd check test and passed as fully clear. Last week we had our first short interval test at severe interpretation and also had to undergo a gamma interferon test. The skin test was again all clear but i have had notice from APHA that two animals are reactors to the gamma interferon test. What surprises me is that both animals are young, 8 month old intensive steers that have been housed since coming onto the farm and have never spent a day outside.
Just how reliable is this gamma interferon test? If the +ve's had been from animals that had been out grazing all summer i would have been disappointed but not surprised. But young, intensive animals that have been housed all their life? Seems strange and surprising to me. Also a large number of resamples to do.

I would be very interested in other peoples comments and experience.

TIA

The use of gamma ifn, is in my opinion, a very blunt instrument.

Yes, it was introduced by the back door, for no veterinary reason, but just if you happened to be in a cull area.
It is only licensed as a secondary or supplementary test and cattle still have to have had clear skin tests to get the restriction lifted. (In Germany they do not use it to slaughter)

Like you, after several years clear, we too had a slaughterhouse case last year and after clear check test, APHA piled in with gamma.
We lost 5 in that sweep all NVL. But like you they failed to get a result from about 12 animals - they also failed to tell us this, so getting these animals tested again, in between 60 day skin tests was a hassle.
Of those 12, two were positive, but 5 couldn't be read. Again. But APHA do not come back a third time - they are classed as a pass.
No we couldn't work that out either.

So the collateral damage for us was around 7 per cent false positives.

I have no problem with the skin test, done correctly. I have a big problem with indiscriminate slaughter of healthy animals for political reasons, while leaving a wildlife culprit free to roam.

 

[epfarms]

The use of gamma ifn, is in my opinion, a very blunt instrument.

Yes, it was introduced by the back door, for no veterinary reason, but just if you happened to be in a cull area.
It is only licensed as a secondary or supplementary test and cattle still have to have had clear skin tests to get the restriction lifted. (In Germany they do not use it to slaughter)

Like you, after several years clear, we too had a slaughterhouse case last year and after clear check test, APHA piled in with gamma.
We lost 5 in that sweep all NVL. But like you they failed to get a result from about 12 animals - they also failed to tell us this, so getting these animals tested again, in between 60 day skin tests was a hassle.
Of those 12, two were positive, but 5 couldn't be read. Again. But APHA do not come back a third time - they are classed as a pass.
No we couldn't work that out either.

So the collateral damage for us was around 7 per cent false positives.

I have no problem with the skin test, done correctly. I have a big problem with indiscriminate slaughter of healthy animals for political reasons, while leaving a wildlife culprit free to roam.

I agree, I think it’s used far too regularly as a sledgehammer to crack a nut. I can see the use when there’s a major, ongoing issue and wildlife culling is also being carried out!

 

[HarryB97]

We went down earlier in the year for the first time and had reactors to the gamma in every pen in every barn on the farm. This is despite all the cattle being bought in as calves and housed since they arrived, the ages ranged from 5 months to 15 months old. All the sheds having atleast 10 foot high walls and electric fencing round them and all the feed is kept inside locked barns. We are now clear but setting up an AFU.

 

[Jackov Altraids]

From my memory of a meeting on this subject, I pointed out that from all the GI test results from the South West, the number found to be positive was very close to being exactly the amount of expected false positives. I was basically told to shut up.

 

[Muddyroads]

Out of interest, how is Tb diagnosed in humans? Presumably they’re not killed and the lungs tested?

 

[matthew]

From my memory of a meeting on this subject, I pointed out that from all the GI test results from the South West, the number found to be positive was very close to being exactly the amount of expected false positives. I was basically told to shut up.

Yup. That sounds about right. Collateral damage.

Out of interest, how is Tb diagnosed in humans? Presumably they’re not killed and the lungs tested?

Pretty much the same as the cattle skin test. The Mantoux (or Heaf) test initially gave a ring of small pricks to the skin on a forearm, which was examined three days later. Any reaction meant X rays, or further investigations, as the candidate had had exposure to TB.

Tuberculosis (TB)

NHS information about tuberculosis (TB), including symptoms, when to get medical help, treatments and causes.

www.nhs.uk

 

[Sosb79]

The GI test isn't fit for purpose, we run a closed heard and don't share borders with any other cattle, we had lesions found in a cow at slaughter so had to GI test, it took 11 cattle out of 120 all of which were clear at slaughter, and two of them were 7 month old calves that had been taken off their Mothers at birth and had never been outside and had been kept in enclosed buildings with sheeted doors! Having spoken to neighbour's they have had the same experience of the GI test and have also lost significant numbers of 6-8 month old animals.

 

[Jackov Altraids]

The GI test isn't fit for purpose, we run a closed heard and don't share borders with any other cattle, we had lesions found in a cow at slaughter so had to GI test, it took 11 cattle out of 120 all of which were clear at slaughter, and two of them were 7 month old calves that had been taken off their Mothers at birth and had never been outside and had been kept in enclosed buildings with sheeted doors! Having spoken to neighbour's they have had the same experience of the GI test and have also lost significant numbers of 6-8 month old animals.

It is fit for the purpose of making sure no cases of TB are being missed but should be used in specific circumstances.
When it has been used throughout a county and the number of positives found is equal to the result that you might expect if no TB was present, that is brilliant news except for the stress, heartache and loss of all those who were affected unnecessarily.

 

[matthew]

It is fit for the purpose of making sure no cases of TB are being missed but should be used in specific circumstances.
When it has been used throughout a county and the number of positives found is equal to the result that you might expect if no TB was present, that is brilliant news except for the stress, heartache and loss of all those who were affected unnecessarily.

I agree with the 'specific circumstances', and they should involve the herd history, location and have a veterinary overview.
Not just because you happened to have put a signature on a paper to attempt to do Defra's dirty work, a few years earlier. And this add on was brought in after the culls began. Many have said that if it had been on the paperwork to begin with, they would not have signed.

 

[An Gof]

Well here is the update. The two Gamma interferon “positive” test animals that were only 8 months old and had never been outside for a day in their life and on an intensive barley system taken for slaughter have both come back negative .......... well that’s a surprise then
Even the head APHA vet when I spoke to him expected them to be negative. What a show the Gamma interferon test is
Two fine animals wasted, compensation that doesn’t cover their value and unnecessary grief and stress for all concerned.

 

[Sheepykid]

Well here is the update. The two Gamma interferon “positive” test animals that were only 8 months old and had never been outside for a day in their life and on an intensive barley system taken for slaughter have both come back negative .......... well that’s a surprise then
Even the head APHA vet when I spoke to him expected them to be negative. What a show the Gamma interferon test is
Two fine animals wasted, compensation that doesn’t cover their value and unnecessary grief and stress for all concerned.

Did those two that were taken pass the skin test previously? We are waiting for two 6 month old cattle to be taken. They’ve failed the skin test but I’m struggling to see how two animals that have never been out of a shed would have it. Luckily they’ve not asked for a gamma test yet.

 

[Werzle]

Well here is the update. The two Gamma interferon “positive” test animals that were only 8 months old and had never been outside for a day in their life and on an intensive barley system taken for slaughter have both come back negative .......... well that’s a surprise then
Even the head APHA vet when I spoke to him expected them to be negative. What a show the Gamma interferon test is
Two fine animals wasted, compensation that doesn’t cover their value and unnecessary grief and stress for all concerned.

Looking on the bright side its good news. I know a few who lost hundreds on the GI test and thought it would rid them of the disease in one painfull hit, it hasnt and they still suffer major tb outbreaks

 

[deleted user 837354]

Gamma test is far too sensitive and likely to declare false positives because of other factors I understood?