Angelfish Aids...Opinions on how long it stays contagious?

My husband I are experienced aquarist/fishkeepers many years of experience between us.
We have made several attempts in 4 tanks of 55 gallons and 75 gallons, to add additional Angelfish to our stock. Both of us had exisiting Angelfish with no previous problems.

Long story short, after several attempt to integrate new Angels from 2 fish stores we exclusively use, we have lost all of them including those we had already had stocked. We are absolutely sure we are dealing with Angelfish Aids. After much time tracking wholesale sources, attempted treatments, talking with several local breeders, we feel confident that is what we are dealing with.
We have seen this before in the 80's when Angelfish stock was pretty much devastated for many years by this disease. There is no real cure for this disease. The disease is rapid, vicious, and literally disenagrates the fish.
I'm am waiting to contact expert C. Robbins for his opinion, however he is on vacation for a few weeks.

I would appreciate any input, experience, and opinions on this.
We will not be stocking any more Angelfish for the time being...

However we are curious about how long the "contagious element" may stay present or active in the tank.

No other fish are affected by this, so we are ruling out major water changes other than 50% and will not break down the tanks (heavily planted) to sanitize. We feel this is too stressful on our healthy established stock.

Anyone found any additional info on the life span of the contagion period of Angelfish Aids once the stock has died off?
Thoughts, experiences, or opinions?

Thanks for your input

Thanks Ted. It does seem possible that the pathogen may be carried by another source also. I believe you are right that, placing Angels back in the tank will be the only way to know for sure. Again, thanks.

As this severe problem has not been studied yet, we can only rely on ourselves. Try putting a couple of young angelfish into one of your tanks in, let us say, a month. Of course you must be sure that these fish are taken from a breeder whose stock is free of Aids/Plaque. Perhaps you should look for some hobbyist, not a shop, to get some really healthy fish. It's difficult, but possible. Then, if they die (sorry, but I can see no other way of finding out), wait one more month and get a few more yound angelfish (I say "young" because they are cheaper), and put them in the other tank. This time you will have a tank that has been left without carriers of the disease for two months. In case the new fish die again you will have to repeat the procedure with all your tanks in which you used to keep angelfish. Perhaps, in several months you will see that new angelfish do not die any more, thus you will determine the period during which the tank remains contagious. Pathogens are not usually able to survive without their carriers for long, and their must be some "dead point" for them. The only thing I fear is that these Aids pathogens may have some intermediate hosts, like snails, or other fishes which do not get ill, but provide them with "shelter" for a time being. Who knows? But let us hope this is not the case.