Abstract: The invention relates to compositions comprising an adenosine derivative and a deaminase inhibitor for the prevention and treatment of parasitic infections by eukaryotic organisms. Parasitic infections which are treatable and preventable with these compositions include malaria, trypanosomiasis, leishmania, toxoplasmosis, sarcocystis, pneumocystis, schistosomiasis, blood flukes and elephantiasis. The invention also relates to methods for utilizing these compositions in treatment regiments. Treatments may be either in vivo or in vitro. In vivo treatments involve administration of compositions of the invention to mammals suspected or at risk of being infected with a parasitic organism. In vitro treatments involve incubation of cells, tissues, biological products derived from living materials or foods with compositions of the invention to inhibit or prevent further infection.