Brainworm, or meningeal worm (Parelaphostrongylus tenuis), is a parasitic roundworm that affects cervids in North America. This species is a slender roundworm commonly found in the brain cavity. White-tailed deer are the normal host for the brainworm, but moose, elk, caribou and mule deer are also susceptible. Brainworm does not affect white-tailed deer. However, in mule deer, moose, elk and caribou, the worm can affect the nervous system of the animal causing weakness, fearlessness, lack of co-ordination of movement, circling, deafness, impaired vision, paralysis and subsequent death of the animal.
Brainworm has a wide distribution in eastern and central North America. Declines in the moose populations of New Brunswick, Nova Scotia, Maine and Minnesota may be associated with this disease.
The worm is of no public health significance because it does not infect humans, and meat of infected animals is safe for human consumption.