TB testing and Reactors (that were overturned)

RE: TB testing and Reactors (that were overturned)

Neil Wheadon — Fri, 26 Jan 2018 13:03:04 GMT

Trawling the memory, I did an investigation on this 8 years ago. The test chart was really suspicious so we asked for the intradermal sites to be collected at PM and sent for histology. I think it proved that something dodgy was happening.

The Irish some years ago had a similar issue where fake reactors were being created. Their answer was simple, all vets were asked to put Bovine over Avian without telling the farmers.

As for contravening proper process, in the days that I was there the vets would ALWAYS defend the OV, as farmers would contact the office querying the test results. (It was quite common) The intradermal test results stood regardless, but if a vet at AHLVA (as it was) wished to do something else it could be done, but the lead VO on TB needed to be asked

Neil

RE: TB testing and Reactors (that were overturned)

Bob Russell — Thu, 25 Jan 2018 17:31:06 GMT

My ex-business partner returned to read a test only to find most were reactors!

MAFF was very good when he held up his hand to say he believed he had mixed the tuberculin up. They were grateful for his honesty (probably a little surprised). The retest was clear!!

RE: TB testing and Reactors (that were overturned)

Neil Wheadon — Thu, 25 Jan 2018 16:46:20 GMT

[quote user="Iain Richards"]Or is there fraud at work? Ive heard of substances being injected to create reactors and gain compensation.[/quote]

YES

There are farmers who will do this. It's pretty easy, if you think about it (pliers over the clip/manure/anything really.

There may also be suspicions of the OV getting the testing methodology wrong. (though with 100 that's pretty unlikely, but you could accidentally inject 20 cattle the wrong way as that's how many the syringe holds)

What jumps out at me here is that if this is a hypothetical case (is it?) then the vet who has gone through the test chart at APHA has used a high degree of common sense and should be applauded.

Neil

RE: TB testing and Reactors (that were overturned)

vs0u — Tue, 23 Jan 2018 22:02:52 GMT

The skin test is something like 80% sensitive, 99.9% specific and the gamma test has slightly lower specificity and higher sensitivity, so to get the numbers you describe would be impossible unless one of the tests didn't work properly for whatever reason. Seems likely that the powers that be have declared them clear because they know there's a problem with the skin test. eg. could the tuberculins have been mixed up?

I've never heard of this happening, but I suppose the compulsory slaughter rule wouldn't apply if they know there was a major issue with the test that caused false results. Have they specified retest in 60 days to clarify?

RE: TB testing and Reactors (that were overturned)

Iain Richards — Tue, 23 Jan 2018 21:37:50 GMT

That sounds so wrong that there has to be an explanation. Has the vet got the avian/mammalian the wrong way round? (Been there, done that). SICCT has 90+% Specificity, so if it's positive it's TB, GiFN is similarly specific so for 50 skin test +ve to be negative on GiFN doesn't sound right either. However, the vagaries of the test, especially in a clean areas where the SICCT have lower PPV and NPV, then if there were a small number of cattle, I can see the test being wrong. Bit not with that number.

Or is there fraud at work? Ive heard of substances being injected to create reactors and gain compensation.