Good question. I really don't know. I didn't breed or raise any of these five chickens on my property but got them all after they were six months old. The round worm life cycle is in eggs deposited in soil from manure. Can be from dogs, cats, wild birds, rats,....The very small larvae crawl up a blade of grass and that grass is in turn eaten by chickens, dogs, cats, horses, ect. They are every where animals are.so I wonder if the kerosene upset the normal healthy balance of worms? Or if they had an overload? Doesn't sound like the later from your description. Interesting none the less
I'm not one of those poop watchers. You know what I mean? I don't pay much attention but I do generally watch where I'm stepping. This is the first round worm I've seen from one of my flock. I find it interesting to find one dead one the morning after treating the water with kerosene. One teaspoon makes a film on the water. I can't even smell it. Maybe it was all a coincidence? I just don't know. But I have been adding garlic and pumpkin to their ff regularly since three months ago.
One worm isn't a big deal but it is making me pay much closer attention.