Parelaphostrongylus tenuis

Parelaphostrongylus tenuis (also known as meningeal worm, brainworm, or moose illness) is a nematode parasite common to white-tailed deer, Odocoileus virginianus, which causes damage to the central nervous system. Moose (Alces alces), elk (Cervus canadensis), caribou (Rangifer tarandus), and mule deer (Odocoileus hemionus) are also susceptible to the parasite but are aberrant hosts and are infected in neurological instead of meningeal tissue. The frequency of infection in these species increases dramatically when their ranges overlap high densities of white-tailed deer.