Molecular characterization and development ofSarcocystis speerisarcocysts in gamma interferon gene knockout mice

Abstract

SUMMARYThe North American opossum (Didelphis virginiana) is the definitive host for at least three named species ofSarcocystis: Sarcocystis falcatula, Sarcocystis neuronaandSarcocystis speeri.The South American opossums (Didelphis albiventris, Didelphis marsupialisandDidelphis aurita) are definitive hosts forS. falcatulaandS. lindsayi. The sporocysts of theseSarcocystisspecies are similar morphologically. They are also not easily distinguished genetically because of the difficulties of DNA extraction from sporocysts and availability of distinguishing genetic markers. Some of these species can be distinguished by bioassay;S. neuronaandS. speeriare infective to gamma interferon gene knockout (KO) mice, but not to budgerigars (Melopsittacus undulatus); whereasS. falcatulaandS. lindsayiare infective to budgerigars but not to KO mice. The natural intermediate host ofS. speeriis unknown. In the present study, development of sarcocysts ofS. speeriin the KO mice is described. Sarcocysts were first seen at 12 days post-inoculation (p.i.), and they became macroscopic (up to 4 mm long) by 25 days p.i. The structure of the sarcocyst wall did not change from the time bradyzoites had formed at 50–220 days p.i. Sarcocysts contained unique villar protrusions, ‘type 38’. The polymerase chain reaction amplifications and sequences analysis of three nuclear loci (18S rRNA, 28S rRNAandITS1) and two mitochondrial loci (cox1andcytb) ofS. speeriisolate from an Argentinean opossum (D. albiventris) confirmed its membership among species ofSarcocystisand indicated an especially close relationship to another parasite in this genus that employs opossums as its definitive host,S. neurona.These results should be useful in finding natural intermediate host ofS. speeri.