Swarms are a source of AFB
There are numerous reports of swarms developing AFB soon after they were placed in a hive.
Swarms are less likely to develop AFB if they are placed on foundation, rather than drawn comb.
When foundation is used, the bees must first draw out comb before beginning brood rearing, and they are therefore more likely to purge themselves of the AFB spores they are carrying before beginning to feed larvae again.
It is also a good idea to initially hive swarms in old equipment so it will not be as costly if the equipment has to be destroyed.
Swarms can carry AFB.