Deer brain worm, Meningeal worm (Parelaphostrongylus tenuis)
The adult brain worm lives in the connective tissue that surrounds the brain of white-tailed deer. In the deer the parasite completes it full life cycle, laying eggs in the brain tissue. Larvae require a snail as an intermediate host. Other herbivores such as the goat can be infected with this parasite if they eat snails carrying the intermediate stage. In the goat, the larvae migrate randomly through the nervous system causing severe neurological disease but the worm cannot reproduce.
Additional animations describing life cycles of parasites that infect the goat.
Haemonchus contortus (barber pole worm)