Andre Norton: Voodoo Planet
Fighting Voodoo is not east but medic Tau has a few tricks of his own

A Free Trader space ship visits the planet Khatka where magic and Voodoo are threatening to destroy the promising civilization that has been slowly developing. The medic Tau uses his own knowledge of magic to help fight this evil menace... but is it enough? Can he fight the very powerful Witch Doctor on his own territory? Listen and find out.