article nonhuman priority journal ornithine decarboxylase Animal Ornithine Decarboxylase Putrescine Trypanosoma cruzi Animals Crithidia fasciculata controlled study eflornithine Eflornithine Ornithine decarboxylase Polyamines Support, Non-U.S. Gov't polyamine putrescine Centrifugation, Density Gradient Leishmania mexicana animal density gradient centrifugation spermidine Spermidine Spermine drug effect enzyme activity protozoon Enzyme Inhibitors Kinetics