Sequence variability in the first internal transcribed spacer region within and among Cyclospora species is consistent with polyparasitism

Cyclospora cayetanensis is a coccidian parasite which causes severe gastroe nteritis in humans. Molecular information on this newly emerging pathogen i s scarce. Our objectives were to assess genetic variation within and betwee n human-associated C cayetanensis and baboon-associated Cyclospora papionis by examining the internal transcribed spacer (ITS) region of the ribosomal RNA operon, and to develop an efficient polymerase chain reaction-(PCR)-ba sed method to distinguish C. cayetanensis from other closely related organi sms. For these purposes, we studied C. cayetanensis ITS-1 nucleotide variab ility in 24 human faecal samples from five geographic locations and C. papi onis ITS-1 variability in four baboon faecal samples from Tanzania. In addi tion, a continuous sequence encompassing ITS-1, 5.8S rDNA and ITS-2 was det ermined from two C cayetanensis samples. The results indicate that C. cayet anensis and C. papionis have distinct ITS-1 sequences, but identical 5.8S r DNA sequences. ITS-1 is highly variable within and between samples, but var iability does not correlate with geographic origin of the samples. Despite this variability, conserved species-specific ITS-1 sequences were identifie d and a single-round, C cayetanensis-specific PCR-based assay with a sensit ivity of one to ten oocysts was developed. This consistent and remarkable d iversity among Cyclospora spp. ITS-1 sequences argues for polyparasitism an d simultaneous transmission of multiple strains. (C) 2001 Australian Societ y for Parasitology Inc. Published by Elsevier Science Ltd. All rights reser ved.