What I believe about Columnaris is that it usually lives on the skin of the fish feeding on dead skin and doesn't cause a problem, maybe even helps.
The problem is when the immune system stops defending the living tissues of the fish. This is usually due to stress.
Then the Columnaris can use undefended tissues as a food source and feed on the gills and even inside the fish on muscle tissue etc.
The time of greatest danger is when acclimatising fish when they have been transported to different environments. The
disease is sometimes already advanced at purchase from the LFS.
We need to choose our livestock sources carefully and ensure that good water quality and a good living environment maintained to avoid problems with Columnaris. Often beginners cannot provide this as they do not have enough experience.
I have not seen evidence in the hobby of Columnaris being cured but antibiotics are a possibility along with other medications.
I have only seen mild cases recover in my aquaria after infected
Neon Tetras were purchased. I did not use medications. I've had a third of my 24 Neons die shortly after purchase, another third died off more gradually and recovery of the remaining third took months. I was able to add healthy fish from a different supplier to bump up the numbers at a later time without incident. This was probably the worst period of my fishkeeping life.
I believe the Columnaris has a resistant resting stage allowing it to survive unfavourable periods so it is difficult to eliminate completely. I wouldn't be surprised if it is present in the air and able to colonise water environments this way.
Different strains have different levels of virulence. The worst strains originate in fish farms where fish density is high. Wild strains are milder.
