Actually, you can NOT tell if a horse will be
positive. As a teenager, back in the 70's, when the test first came out,
my palomino quarter horse mare tested positive. She was strong, fast, well
fleshed, and had no symptoms of anemia or even a runny nose. She had been
exposed to the disease at some point before she came into my possession, and
made the antibodies, which is all the test looks for. We still don't have
a cheap, reliable test for the disease itself, just the immune system's response
to it. Who knows if she had ever even had the disease? All it tests
for is exposure.
Which is also why there are false negatives - a
horse can be ill with Equine Infectious Anemia, but incapable of producing the
antibody - so he will test negative.
