The Collaborative International Dictionary of English v.0.48:

Filaria \Fi*la"ri*a\, n.; pl. filariae. [NL., fr. L. filum a
   thread.] (Zool.)
   a small, slender nematode worm of the family Onchocercidae
   (Filariidae) of many species, parasitic when adult in
   various animals, including man. They may live within the
   blood, or in other bodily fluids, or within tissues or
   cavities of the body. Infection with such organisms may be
   transmitted by blood-sucking arthropods.
   [1913 Webster +PJC]