The Collaborative International Dictionary of English v.0.48:

Filariasis \Fil`a*ri"a*sis\, n. [NL.]
   1. (Zool., Med.) the presence of filariae within the body of
      an organism; infection with filariae. It is mostly found
      in tropical and subtropical regions.
      [Webster 1913 Suppl. PJC]

   2. (Med.) a disease caused by nematodes in the blood or
      tissues of the body causing blockage of lymphatic vessels.
      Death of the adult worms may lead to inflammation and
      permanent fibrosis; the condition may lead to serious
      symptoms, such as elephantiasis or blindness. See river
      blindness
      [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

filariasis
    n 1: a disease caused by nematodes in the blood or tissues of
         the body causing blockage of lymphatic vessels