Meningeal worm, or brainworm.
|Photo by DEC's Wildlife Pathology Unit|
Species: P. tenuis
Physical Description: P. tenuis, or brainworm, is a roundworm found in the venous sinuses or subdural space of the brain (Maze and Johnstone 1986). It normally parasitizes white tailed deer in eastern North America. It has only been known for the past 60 years and most research done has focused on wildlife management implications.
Ecology: The brainworm is found throughout eastern North America where white-tailed deer exist, mostly deciduous and coniferous-deciduous forests. It has been reported from Nova Scotia down to Georgia and Mississippi. Although its normal and preferred host is the white-tailed deer, brainworm also infects moose, elk, caribou, reindeer, mule deer, goats, sheep, alpaca and even guinea pigs. The brainworm is more often found in moist environments, but can be found anywhere deer populations inhabit. Males and female deer are infected in equal proportions, though about 80% of affected animals are not fully mature.
|Photo retrieved from Michigan |
Department of Natural Resources
The worm starts life cycle by depositing eggs around the host’s brain, or bordering blood vessels. Once the eggs hatch and young emerge, the larvae penetrates small blood vessels and are transported into the lungs. Once in the lungs, they enter the bronchioles and move up the respiratory tract until they reach the throat. They are then swallowed and go through the intestinal tract, eventually coming out in a mucus coating around the deer fecal pellets. The worm then depends on an intermediate host, gastropods, to feed on infected deer fecal matter (Duffy et al. 2002). After a development inside the intermediate host, the larvae becomes ready for deer. It is at this time that the parasite must get lucky and hope that a browsing or grazing deer consumes the gastropod. Once eaten, the worm penetrates the wall of the new host’s small intestine and enters the body cavity. Migration along nerves to the spinal cord then take place and once inside the spinal cord, the worm can begin to grow. After a short time, they continue migrating along the spinal cord up to the subdural space surrounding the brain. Once there the worms continues to grow into maturity and complete their life cycle.
This maturation inside the deer takes between 80 and 90 days, at which point larvae will begin appearing in feces. Once matured inside a deer, the brainworm can persist in a single host for many years (up to 3.7 years, probably longer), allowing many larvae to make it out into the feces (Duffy et al. 2002). The infected white-tailed deer is usually unaffected by the brainworm, although if moose, mule deer, llama and a range of other animals be infected, death is soon to come with few ever depositing larvae in their feces.
Interesting tid-bits: As early as 1912 in Minnesota, moose were being identified as having a sickness, a disease. It was characterized by blindness, lack of fear for humans, aimless wandering and ataxia. Analysis of diseased animals concluded irreversible damage to the central nervous system. People knew by the 1950’s that this “moose sickness” occurred with the presence of white-tailed deer but it wasn’t until 1964 that Anderson (1964) discovered that a nematode cause the sickness! It has since been identified as a limiting factor to moose where populations overlap with white-tailed deer (Gilbert 1974; Lankester 2010).
Anderson, R.C. 1964. Neurologic disease in moose infected experimentally with Pneumostongylus tenuis from white-tailed deer. Pathologica Veterinaria 1: 289-322.
Duffy, M.S., T.A. Greaves, N.J. Keppie and M.D.B. Burt. 2002. Meningeal worm is a long-lived parasitic nematode in white-tailed deer. Journal of Wildlife Diseases 38: 448-452.
Gilbert, F.F. 1974. Parelaphostrongylus tenuis is Maine: II prevalence in moose. The Journal of Wildlife Management 38: 42-46.
Maze, R. J. and C. Johnstone. 1986. Gastropod intermediate hosts of the meningeal worm Parelaphostrongylus tenuis in Pennsylvania: observations on their ecology. Canadian Journal of Zoology 64: 185-188.
Lankester, M.W. 2010. Understanding the impact of meningeal worm, Parelaphostrongylus tenuis, on moose populations. Alces 46: 53-70.