Ditto frontline, although I have heard of the ivermectin injection. The only prob with frontline is that it is exspensive if you have lots or horses to do. My friends cob passed it to ours. We did two treatments and managed to clear our girls, however my friend refused to do hers a second time as she thought that it had worked well enough the first time. Suprise suprise the problem came back.
I was worried that my girls would pick them up again so I doused feet and legs with a herbal inscecticide powder on a weekly basis. It seemd to work. I wouldn't recomend using a herbal product to try to clear them, just to prevent them