Altum wrote,
according to experts with microscopes
neons and cardinals can both be infected with Pleistophora
hyphessobryconis. So can most other tetras and many cyprinids.

It's hard to argue with a microscope, but there must be somewhat of a
resistance for the statement to come up so often and in so many sites.

Consider the possibility that the wild-caught
cardinals in your store had some immunity to NTD while the farm-raised
neons and other tetras didn't...

Most of the time I bred the cardinals for our stores. I would suspect
that it's the tank raised cardinals that would have more of a
resistance to NTD than the wild or pond raised cardinals... About the
only time I see what looks to be NTD, is in the big chain stores with
central filtering. Quite often one can see a neon tank down with the
disease, but the cardinals will be looking good. Then again, most of
the time I beleave the symptoms are misdiagnosised as some bacterial
infections mimic NTD. If Nalidixic Acid or protiozin treatments are
successfull (as with most of the time), the disease was misdiagnosised.
I sold to other stores other than our own - a few times the owners of
the stores would close a tank due to NTD, which to date is untreatable.
They would give me the tank of neons, which *most* of the time, when
treated were cured, so was nothing but a bacterial infection. Like
those stores, most people misdiagnosis the symptoms, thus won't even
treat, but trash the fish. Like I said, most cardinals are tank bred
now, while neons are still brought in from the wild - mabe some gene
therapy going on here (?) ................... Frank