I might disagree here, on a few points. Typically most agree most if not all internal parasites are killed in 30-48 hours at -7ºC. I have had one snake with internal parasites and was told that it is common for rats to carry parasites and most breeders do not to fecal exams on the populations due to cost and complications.

It is easy to assume that all rats have some and that they can be passed along (many can't be but) and just do the best you can to limit the possibility. It costs nothing more than time and can save vet bills there is no downside.