Columnaris is a quick, highly contagious, and fatal disease. Usually when water is too hard or a fish is stressed by overcrowding. It starts by getting into a betta, usually through gills and small wounds. The betta's fins get frayed and ragged. It is followed by appearance of ulcerations on the skin, and subsequent epidermal loss, identifiable as white or cloudy fungus-like patches. Gills will change color, to a brown or light brown. The betta will breathe rapidly and laboriously as a sign of gill damage. Death (without treatment) will happen in 48-72 hours, sometimes less when the water is hot. Treat the betta with Furan-2 and Kanamycin (antibiotics). Medicated food containing oxytetracycline is also a good thing to feed the infected betta.
I thought I should post this because some symptoms of Columnaris is going around Bettafish.com :)
(According to OFL< there is slow and fast-acting Columnaris)