DX

Prions are the simplest disease-causing entities known, even simpler than viruses. They are protein fragments. They are so simple they can't even invade a body. They have to be passively ingested.

In The lost World
It was theorized by Ian Malcolm that the Dinosaurs on Isla Sorna developed a prion disease called DX, from a bad batch of sheep protein extract. The dinosaurs were being fed sheep's milk. The prions are excreted in feces. The Compys were scavengers and used on the island as waste management; they spread the protein over carcasses, and other scavengers became infected. Eventually all the Raptors were infected. Raptors attack healthy animals, not always successfully. One bite and the animal becomes infected.