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Meningeal Worm ("Brainworm")

Brief Description

White-tailed deer are the natural hosts for the meningeal worm Parelaphostrongylus tenuis.  White-tailed deer typically
Photo courtesy of Michigan Department of Natural Resources

 Note the meningeal worm in the meninges inside the skull.

Photo courtesy of Michigan Department of Natural Resources


harbor meningeal worm without any signs of disease.  In most other Cervidae, including elk, infection can result in neurologic problems and fatal neurologic disease.

Public Health Implications

None reported.

Causative Agents

Meningeal worm is caused by the roundworm (nematode)Parelaphostrongylus tenuis. The intermediate host is one of several species of snail or slug. Animals become infected when they ingest infected snails or slugs, likely by accident.

Clinical Signs

Symptoms of the disease are:

  • aimless wandering or circling
  • listlessness
  • loss of fear of humans
  • standing alone (an unusual behavior in herding animals like elk)
  • ataxia
  • lameness
  • stiffness
  • general and lumbar weakness
  • blindness
  • abnormal positioning of the head and neck
  • paraplegia
  • death


The roundworm infects the area in or around the brain and spinal cord. Microscopic examination can find “tracks” of the worm moving through these areas. Occasionally, a thin, hair-like worm can be found in the area surrounding the brain.


Diagnosis is made by finding “tracks” the worm has left through the spinal cord or brain, usually only visible under a microscope. Additionally, the thin, hair-like worm can be found in the meninges between the brain and skull.

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