Usually poultry lice (which are different than human/mammal lice) come from wild birds.
We’ve had a couple instances of lice. But, now that wild birds cannot get into our setup as easily, we haven’t had any instances.
That’s great! I’m glad the lice died.
We’ve washed many chickens. Normally you do not want to wash chickens bc off their natural oils. However, sometimes, like now (for you), you need to. For us, most of our chicken washing happens at fair the day before the chicken judging. Here’s a...
Permethrin works well. We clean coop and thoroughly spray everything. Add fresh litter, then we close coop.
Catch chickens 1x1 with helper. Hold upside down, spray vent, between legs, under wings. Then put into clean coop. Repeat in 7-10 days to get the lice that have hatched.