It's so hard to say. It could be viral. I highly doubt it's husbandry-related, they take excellent care of their chameleons.
Edit - I was on my phone and I hate typing on it but I wanted to say, if Karen comes across this thread, that I'm so sorry that this is happening to them. I was shocked when I came across their post on FB on this earlier, and I'm so sorry that they're going through this.
Thanks Olimpia. I hope it ends soon ...
I assume all the melleri were exposed to each other through sharing a room or other space, using the same equipment for watering, feeding, etc? So, trying to isolate any of them now may not change anything. And, as you have other species that are not having these problems it can't be some sort of environmental contaminant/toxin?
BTW, finding the roundworms everywhere may just be a sign that that particular cham was heading into trouble early enough that it allowed their population to explode.
Sorry if I don't know much about your melleri, but are they related, wc, cbb? Are they different ages? Just trying to think about other problems that could be linked to some sort of common heredity (and a shared sensitivity to something).
Again, I'm so sad to hear this! Melleri are special!