White-tailed deer
White-tailed deer ("Odocoileus virginianus") commonly carry meningeal worm or brainworm, a nematode parasite that causes reindeer, moose ("Alces alces"), elk ("Cervus canadensis"), and mule deer ("Odocoileus hemionus") to develop fatal neurological symptoms which include a loss of fear of humans. White-tailed deer that carry this worm are partly immune to it.