Strangles - Is this Strep Protein M Test?

[ChipperKipper]

Hi, I'm in the process of buying a horse and the new livery yard requires a negative strangles test. We have had a blood test done which came back as 106% (the lab report says anything under 100% is negative, anything over 100%) is positive. I'm used to the Elisa 0 -> 1 scale, but the lab report says that this test is an Elisa one... yet it sounds more like the Strep Protein M Test. Unfortunately the vets can't explain which test it is, or explain what the full scale is. I.e. how high does it go, 0 -> 1000, for instance?

Can anyone help explain whether this is a borderline positive or a significant positive, whether it is indeed the Strep Protein M Test - and if so, how high the results scale goes, and which next step would be recommended?

As far as I can tell the options are a) do another blood test, or b) go straight to the guttural pouch wash.

Thanks in advance for any assistance!

 

[Caol Ila]

The blood test is, as far as I am aware, always an ELISA one. But I don't even play a vet on TV. The way the results are presented is odd, though. When I have had a strangles blood test done, the results come back on that 0 - 1 scale.

The last time I moved yards, my horse had a positive ELISA test, a surprise to me since she hadn't been anywhere. I did lots of research and learned that it's common. It's an antibody test (which you probably know), and those antibodies can hang around in the blood for six months, or longer. All they mean is that your horse had some exposure in the last six months, enough for an immune response but not necessarily enough to get sick or spread an infection. Strangles is pretty endemic amongst the equine population, so you can easily have mild exposure that doesn't come to anything at horse shows or whatever. Then the horses who went to shows bring it to ones who stayed at the barn. But at such low levels that you would not know unless you did an ELISA test. The issue is that some horses are asymptomatic carriers, so they can be infectious to other horses without presenting with strangles themselves. The blood test is useful for picking those up.

It also takes about two weeks after exposure for antibodies to appear. This is how it gets through the net. A horse can be infectious but have a negative ELISA test.

However, the gold standard for determining whether a horse has an active infection is the gutteral pouch wash and PCR test. It's invasive and expensive (yikes!) but will give you a definitive answer. You can also retest the bloods in two weeks (the reason being the above paragraph...if it is symptom free, it's probably not infectious, unless it's a carrier), but when I had to make that call, it seemed to me that if the antibodies hang around for a while, I might end up in the same place, only with delays and more vet bills and even more stress. In my case, it was a horse I'd already owned for a while and I just wanted to get her moved, so I went with the wash straightaway.

It feels like it would be a trickier situation with a horse you are in the process of buying. That's like a £400+ vet bill for a horse you might not be in full posession of yet, and if the PCR does come back positive, then what? Can you back out of the sale? Should you? I dunno.

 

[ChipperKipper]

The blood test is, as far as I am aware, always an ELISA one. But I don't even play a vet on TV. The way the results are presented is odd, though. When I have had a strangles blood test done, the results come back on that 0 - 1 scale.

The last time I moved yards, my horse had a positive ELISA test, a surprise to me since she hadn't been anywhere. I did lots of research and learned that it's common. It's an antibody test (which you probably know), and those antibodies can hang around in the blood for six months, or longer. All they mean is that your horse had some exposure in the last six months, enough for an immune response but not necessarily enough to get sick or spread an infection. Strangles is pretty endemic amongst the equine population, so you can easily have mild exposure that doesn't come to anything at horse shows or whatever. Then the horses who went to shows bring it to ones who stayed at the barn. But at such low levels that you would not know unless you did an ELISA test. The issue is that some horses are asymptomatic carriers, so they can be infectious to other horses without presenting with strangles themselves. The blood test is useful for picking those up.

It also takes about two weeks after exposure for antibodies to appear. This is how it gets through the net. A horse can be infectious but have a negative ELISA test.

However, the gold standard for determining whether a horse has an active infection is the gutteral pouch wash and PCR test. It's invasive and expensive (yikes!) but will give you a definitive answer. You can also retest the bloods in two weeks (the reason being the above paragraph...if it is symptom free, it's probably not infectious, unless it's a carrier), but when I had to make that call, it seemed to me that if the antibodies hang around for a while, I might end up in the same place, only with delays and more vet bills and even more stress. In my case, it was a horse I'd already owned for a while and I just wanted to get her moved, so I went with the wash straightaway.

It feels like it would be a trickier situation with a horse you are in the process of buying. That's like a £400+ vet bill for a horse you might not be in full posession of yet, and if the PCR does come back positive, then what? Can you back out of the sale? Should you? I dunno.

He's an ex-racehorse but has lived on his current yard for a fair number of years. It is a private yard that doesn't have horses coming and going so the current thinking is that it must be antibodies from when he was on a racing yard and went out to competitions (although that would be longer than 6 months ago). The results are really are strangely presented, and even the vet can't interpret them! But I do think the wash might be the only conclusive way to go.

 

[Widgeon]

The results are really are strangely presented, and even the vet can't interpret them! But I do think the wash might be the only conclusive way to go.

If that's the case surely your vet should go back to the lab and say, this isn't the usual presentation and I don't know what it means - please provide these results in the standard way. Presumably someone has paid for these effectively useless results? I'd be pretty hacked off if I paid for a blood test and my vet didn't understand the lab's results.

 

[BronsonNutter]

It will be the M protein test. I've had positive cases (asymptomatic carriers, PCR positive on guttural pouch wash) where the results have come back between the 100-110 range on that test, and so I would get the horse guttural pouch washed.

 

[HorsesRule2009]

With the results you have as you say anything over 100 is classed as positive, so advice is always to GPW there is no other way to get the result.
If the horses hasn't really left the yard the likely hood of the results dropping if you wait the 2 - 4 weeks before re doing bloods is very slim.
As said above some horses with high bloods can be carries of strangles and not show symptoms themselves.
Good luck

 

[ChipperKipper]

Thanks everyone for the responses. We did the GPW and the results were negative (just in case anyone else finds this thread and would like some potential reassurance!)