I think carriers are sort of like a needle in a haystack. I know there are possible carriers but it could be a pheasant, chicken, turkey or another peafowl. Blackhead comes from a parasite in an earth worm and could be anywhere. I do take precautions for blackhead. Juveniles are much more prone to get it if they are put on the ground young. I try not to put any birds on the ground till after they are at least 6 months. I keep metranizadole on hand all the time. I have had very few cases over the years. In fact chickens hatch most all my peacocks and have for the last 30 years.