Mammalian prions propagate by template-directed misfolding and aggregation of normal cellular prion related protein PrPC as it converts into disease-associated conformers collectively referred to as PrPSc. Mammalian species may be permissive for prion disease because these hosts have co-evolved specific co-factors that assist PrPC conformational change and prion propagation. We have tested this hypothesis by examining whether faithful prion propagation occurs in the normally PrPC-null invertebrate host Drosophila melanogaster. Ovine PrP transgenic Drosophila exposed at the larval stage to ovine scrapie showed a progressive accumulation of transmissible prions in adult flies. Strikingly, the biological properties of distinct ovine prion strains were maintained during their propagation in Drosophila. Our observations show that the co-factors necessary for strain-specific prion propagation are not unique to mammalian species. Our studies establish Drosophila as a novel host for the study of transmissible mammalian prions.