Our 4 weaners suddenly seemed to get a massive lice infestation - one day I saw a couple on each weaner and then it seemed like the next day each pig had about 20.
An effective method to control them is to use vegetable oil - spray it on the neck and behind the ears and basically anywhere you see the lice - the oil clogs up the spiracles of the lice effectively suffocating them.
The day after doing this to our pigs they were back to being lice free
I got this tip from our vet who said they could prescribe a medication but the smallest amount he could give us was sufficient for a commercial pig herd so basically a massive waste. He said the oil would work fine and it seems to just fine
I've used it on all our batches of pigs with great success