Opossums (D. virginiana, D. albiventris, and D. marsupialis) are denitive hosts and a parasite has been found in the United States, Argentina, and Brazil.414,416,423,426,427 The parasite has been transmitted from the South American opossum to the North American opossum via infections induced in the KO mouse experimental intermediate host.428 Sporocysts from experimentally infected opossums are 12-15 × 8-10 μm in size. The natural intermediate host for S. speeri remains unknown.