Hello & welcome, I am Dr. B, a licensed veterinarian and I would like to help you with your wee one today. I do apologize that your question was not answered before. Different experts come online at various times; I just came online, read about your situation, and wanted to help.
Now you have not noted the purpose for testing Willow, Hope, and Cole. As I am sure you can appreciate, we test for Strangles for a variety of reasons (ie to diagnose the disease in an ill horse, to identify carriers of the bacteria, to identify if a particular horse has been exposed to the agent, to prevent introducing it into a boaring stables, etc). And because of this, some testing routes will be better for some cases.
In this case, you mentioned that they were swabbed for Strangles and were negative. When using this means of testing, we tend to need to repeat it three times (a week apart) before we can officially call those animals negative for the bacteria. The reason for this is because it is possible to get false negatives on a single swab (if the bacterial shed was low, if the bacteria died in the post before it got to the lab for culture, etc). If the animal is negative on each occasion, then we assume they are not carrying or shedding the bacteria (but we cannot say if they have or have not ever been exposed to it)
In regards XXXXX XXXXX this test, it is of most benefit when we have potentially actively infected animals or carriers who could be shedding the bacteria. Those who have had the disease before and recovered from it, will be negative with this test (since the bacteria has to be present to cause a positive result on swab). When using blood tests, we tend to use them in cases where we are moving/introducing horses to a new group, or if we are trying to ID of potential carriers after an outbreak.
In regards XXXXX XXXXX blood test, this can be useful but again depends on what we are trying to achieve with testing. We only need to test one time but the blood test doesn't look for the bacteria like the swab does. Instead it tests for the horses' antibody levels against this bacteria. By using a single blood sample, we can identify diseased horses (if they are showing clinical signs), those who have been exposed in recent months, those who have immunity (from past infection), and those who are carriers. If positive, the blood test cannot tell you which is the case for the horse in question. And if a positive is found, then swabbing would be the only way to determine if the animal is actively carrying and/or shedding the bacteria. Just to note, if these horses were exposed to strangles less then a fortnight ago, then we can get false negatives on the blood test (since the antibodies won't be at significant levels yet).
Overall, whether you need the blood test depends heavily on the situation you face. If you can provide some background information, I am happy to work with you to determine if a blood test is indicated or if we need further swabs here. Otherwise, if you are introducing these horses to a new group or trying to check for carriers, then bloods would be useful here. And if that is the case, I would just note that the Animal Health Trust (AHT) has the most specific/sensitive test for Strangles antibodies and the results tend to only take 24hours to be processed by their lab.
I hope this information is helpful.
If you need any additional information, do not hesitate to ask!
All the best & happy holidays,
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