We originally purchased a #17 sickly red sex-links. After 6 weeks 3 survived a closed eye, illness. After 4 months of the three healthy birds I hatched #40 chicks, mix id Rhode island reds and barnyard mix. These are now about 12 weeks old. This morning I found a 12 week old with a puffy eye just laying around. Help, will this spread? What can I do to get a better handle on this?