Tim,
This knife could also be Fulani (other names are Fulbe or Peul) who live in the neighbourhood of the Hausa.
I read in a book that the Fulani used the lost-wax technique to cast the handles of their arm daggers. Yours looks like it is made this way.
I have a similar knife (but not as good as yours

) without sheath.
Could we see your dagger out of its sheath ?