Can I get a prion disease from eating calf brains or only by handling uncooked ones?

Either potentially. Cooking does not inactivate the malfolded infectious prion protein nor does formalin treatment. It was shown decades ago that brain in formalin for years could transmit cjd.
Avoid any ingestion. Eating or handling infected brains can lead to transmission and infection. The only reliable way to destroy prions in tissue is immersion in fomalin for up to 4 wks.