Filariasis (or philariasis) is a parasitic disease caused by an infection with roundworms of the Filarioidea type.These are spread by blood-feeding black flies and mosquitoes. This disease belongs to the group of diseases called helminthiasis.Eight known filarial nematodes use humans as their definitive hosts. Lymphatic filariasis is caused by the worms Wuchereria bancrofti, Brugia malayi, and Brugia timori. 2  These worms occupy the lymphatic system, including the lymph nodes; in chronic cases, these worms lead to the disease elephantiasis.