Cellulitis is just plain a pain in the ass.
I’ve posted about my TB (also on that scabby thingy thread posted above). Interestingly, he got cellulitis in the same week (always the last few days of June) 4 years in a row. It’s always been in the driest part of the summer when he’s standing in the least possible amount of muck/mud. And that’s compared to the 9 months of spring/winter/fall when all of my horses are in actual mud almost 24/7 (or at least have access to mud all day/night). And then additionally, 2 of the 4 years we were at a horseshow where he was standing in a totally and completely clean stall when it struck.
And then the other 2 times were at home days before we left for the show. Again, no mud, no muck, nothing that you would typically think of as an irritant of any sort.
One of the times at the show the vet peeled off one of his scabby things, smelled it, and said, “yuck! There’s your source of infection!” So potentially the little scabby things were the entry point. But none of his scabbies were knocked or cracked or seemingly offering an actual entry point (and certainly not compared to when they’re softer in the winter and often knocked off). But then the year before my vet pointed to where a scab had recently been peeled off and said, “whelp, there’s your entry point!”
Oh and then one of the years at the show he got a lesser version of his cellulitis and then one of my other mares (she was 20yo at the time and had never in her life had cellulitis, and didn’t/doesn’t have the scabbies nor any scrapes/wounds of any kind on her leg) also got cellulitis that was far less aggressive and responded immediately to antibiotics. So in that case I wonder if it was some sort of a virus or pathogen at the facility or in the shavings or somehow related to where we were. Orrrr it was just a weird coincidence.
And then last year, after 4 years of cellulitis attacks in the last week of June, my guy had his “annual” 2017 attack in January. And then I’m still awaiting the 2018 episode.
So all of that to say that I don’t think there’s always rhyme or reason to cellulitis attacks. I don’t think you can “prevent” them when you’re battling something at least somewhat systemic. It might be a different story with a horse that gets cellulitis as an over-reaction to a wound. But I feel a little more hopeless about horses with the perma-scabbies.