I've adopted three greys in the last 2 1/2 years. One was in the kennel for almost a year, one came from being in foster care for two months (although she did spend a little time in the kennel before I got her), one came from a brood farm (was also at the kennel for a little while). I've also had about 8 fosters that have all come from the kennel and fresh off the track. (BTW, my adoption group is GPA Houston)
I've never had any of these dogs come with parasites of any kind. Maybe we have a great kennel, maybe I was just lucky...I tend to think it's the former. Our kennel dogs are pretty well cleaned up, I've never had one come home with a tick, fleas, or anything else.