Yes, it can affect any breed of sheep or goat. In sheep, some are genetically resistant to the disease. You can select for Scrapie resistant sheep by purchasing an RR ram and breeding him to your unknown ewes. Or having all your sheep genotyped and culling the QQ stock.
Sheep that are RR at Codon 171 are genetically resistant to two of the I believe three strains of Scrapie. QR sheep are genetically resistant to at least one strain. QQ sheep at Codon 171 are susceptible to the disease
if exposed to it. Generally if your sheep are QR or QQ it is recommended to have them tested at Codon 136 (which is the genetic susceptibility to another strain of Scrapie). For the most part, all RR sheep are AA at Codon 136. QR & QQ sheep can be AA, AV, or VV at Codon 136.
To my knowledge there is no genetic resistance test for goats. However, it is not as common in goats as it is in sheep.
Usually Scrapie is passed through birthing fluids and bedding/soil touched by birthing fluids.
While it is a serious, fatal disease, it is not overly common. Most sheep don't have it. Especially now with the Scrapie Eradication program in place (
www.eradicatescrapie.org), there have been fewer and fewer Scrapie cases every year.
Whether buying a sheep or a goat, you should ask and see if they are involved in the Scrapie Eradication program (voluntary or mandatory). Regardless, if you buy any animal it is a legal requirement they have a Scrapie ID tag put in by their farm of origin (where they were born). That way they can be traced back to the potential source (remember how Scrapie is primarily passed through birthing fluids?) and further investigation can take place.