Question about Quarantine...

I have a question about how you quarantine a new guinea pig. If guinea pigs can have mites without showing symptoms, if you quarantine a pig for 3 weeks and it shows no symptoms but really does have mites, won't it still pass them on to the other pigs? Is this why some people routinely treat all quarantines for mites? Also, what is the BEST way to routinely treat a quarantine pig for parasites that is not showing any symptoms? I've read that Ivermectin works great on mites but won't kill lice, so would you have to use something different to treat for lice too? Or I have read that Revolution kills both mites and lice, so if you treated with this during quarantine would that cover everything?