Meningeal Worm

Common Name - Meningeal Worm

Category - Roundworms

ScientificName - Parelaphostrongylus tenuis

Kingdom - Animalia

Phylum - Nematoda

Class - Chromadorea

Order - Strongylida

Family - Protostrongylidae

Genus - Parelaphostrongylus

Species - tenuis


Description - Long, fragile, threadlike roundworms, also called nematodes; brown in color; adults visible without magnification; located in the membranes surrounding the brain, called meninges, and in the venous sinuses of the cranium in white-tailed deer

Size - Adult worms are approximately 2 inches (50 mm) in length; eggs and larvae are microscopic

Ecological Role

Fun Facts






Habitat - Mostly moist or wet environments but cannot exclude dry areas

Kentucky Distribution - Areas where intermediate snail host and white-tailed deer are abundant; distribution of the meningeal worm widely extends across the central and eastern portion of the United States.

Life Cycle - The life cycle of the Parelaphostrongylus tenuis nematode requires two hosts. The definitive host is the white-tailed deer. The intermediate host is a gastropod such as a slug or snail. Both hosts are required in order for the meningeal worm to complete its life cycle.

Adult meningeal worms deposit their eggs either in the meninges or directly into blood vessels of the definitive host. The eggs are transported by the blood stream to the lungs where they invade the air sacs, or alveoli, and develop into first stage larvae, or L1. The larvae are coughed up, swallowed, then eventually passed with the feces of the deer. The larvae penetrate the skin of the intermediate host as it crawls over soil or grass contaminated with the infected feces. This is an important stage in the life cycle of the meningeal worm. In approximately 21 days the larvae develop into an infectious third stage larvae, or L3, within the gastropod. Deer inadvertently consume the infectious gastropods while grazing. The infectious larvae penetrate the stomach of the deer and migrate to the spinal cord where they develop for about 3.5 to 4 weeks before migrating to the meninges and completing their life cycle as adults.

Life Span

Life Stage


Seasonal Changes - Repeated freezing or long dry periods help control the L3, or infectious, stage of the meningeal worm.


Status - Potentially fatal to elk, moose, goats, sheep, lamas and alpacas; generally not fatal to white-tailed deer




What We Can Do - Control methods to guard wildlife against exposure to the nematode are not feasible at this time. Many infected wild animals overcome the illness and remain viable and reproductively important to the herd.

Domestic animals such as goats, sheep, alpacas and lamas can be de-wormed on a regular basis to control the spread of the nematode. Exclusion fences may be used to keep white-tailed deer from sharing pastureland with domestic herds. However, exclusion fences may not be a feasible control method without discouraging the migration of snails and slugs onto the same pastureland.


Diagnosis and Control - Observations of the suspect animal and exposure history of white-tailed deer habitat help in clinical diagnosis. Affirmative diagnosis of meningeal worm infection is confirmed through a necropsy.

Interesting Facts - Meningeal worm is also called brainworm. Infestation of up to 20 worms has been discovered in a single deer’s subdural cavity. 

As the preferred host for meningeal worms, or Parelaphostrongylus tenuis, white-tailed deer rarely suffer neurological or sickly problems from this worm. However, severe brain and spinal cord damage arises in elk or moose when they are exposed to meningeal worms. Symptoms of infected animals may include weakness, loss of appetite, dementia, clumsiness, head tilt, separation from the herd, walking in circles, fearlessness, paralysis, and potential death. Meningeal worm can also affect domestic goats, sheep, alpacas, and llamas.

Meningeal worm is not a health concern for humans. Consumption of a deer or elk with brain worm is not hazardous to humans and is considered safe to eat.

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