- Wuchereria bancrofti is a filarial nematode responsible for lymphatic filariasis (elephantiasis).
- Brugia malayi is another filarial nematode causing lymphatic filariasis in Asia.
- Leishmania donovani causes visceral leishmaniasis (Kala-azar), not filariasis.
- Trypanosoma gambiense causes African sleeping sickness, not filariasis.
\(⇒\) Filariasis is caused by \textbf{Wuchereria bancrofti and Brugia malayi}.
\fbox{Thus, the correct answers are (A) and (C).}