Parelaphostrongylus Tenuis

Parelaphostrongylus tenuis (brainworm or meningeal worm) is a small parasitic nematode that infects the brain of many ungulates. Its natural host, the white-tailed deer, is unaffected by its presence; other species, however, suffer severe neurologic damage that eventually leads to death. This disease is known as moose sickness for its frequent occurrence in moose sharing territory with white-tailed deer.

Parelaphostrongylus tenuis was identified as the cause of moose sickness—a disease known since 1912—by Canadian biologist Roy Anderson in 1963.