Funny, I was just thinking this today, and trying to remember if my mother in laws dog had acted differently around my wife since she got MECFS. Couldn't reallly recall.
A friend of mine posted a video the other day of a pug coming up to her when she was on a walk and then just sitting next to her and looking back in the direction she came from. Apparently she was deaf and lost. What I found interesting was my friends dog sniffed this Pugg all over and then came back to the ears for additional sniffs. Could smell that the pug was deaf.
My dogs also become very protective of me during a POTS flare, @IThinkImTurningJapanese. However, they have yet to actually detect and alert me before it happens (it would be handy if I knew how to train them to do so, they would be pretty busy of late 😬).
Can't say I've heard of dogs being trained to detect the presence of ME in an individual, though.
My guess is that dogs might sense 'sickness', but it wouldn't be specific to ME. It's kind of hard to train dogs to reliably sense ME when we have no way yet of knowing which person with ME-like symptoms actually has ME, and is thus a suitable training subject.
If we have some biochemical imbalance, we may as well have our own specific scent and dogs may pick that up. I think it would be worth a try, to train a dog first with very severe cases that are bedbound and then test it with less severe people but who also have clear symptoms.
I suspect the way they trained dogs to do it with covid is they expose the dog to subjects and controls and when the dogs react to the subjects they get praise and a treat. So it would not require our knowing anything about a disease other than being able to differentiate between those that have it and those that don't. That way we know when to reward the dog. With covid they do this with pcr or antigen test. With CFS/ME it would be the patients word because that is all we have. I think what they do is have you hold some type of tissue under your armpit for a few minutes and then they expose it to the dogs. I think they radiate them first so to prevent the dog from contracting the disease.