Molecular characterization of Cyclospora-like organisms from baboons

Cyclospora organisms are intestinal pathogens of humans that are increasing ly recognized in many parts of the world; yet, the reservoirs and host rang e remain poorly defined. Analysis of 18S ribosomal DNA (rDNA) suggests that the human-associated Cyclospora species (Cyc-hu) is most closely related t o the Eimeria species, which are host species-specific. Recently, oocysts i dentical to those of Cyc-hu were detected in baboon fecal specimens from Ta nzania, The 18S rDNA from 3 of these baboon-associated oocyst specimens was amplified and sequenced. Phylogenetic analysis indicated that these baboon -associated Cyclospora-like organisms (Cyc-bab) are nearly identical to eac h other and are distinct from Cyc-hu (1.6%-1.7% dissimilar); however, these Cyc-bab organisms are the closest known relatives of Cyc-hu. Together, the se primate-associated cyclosporans constitute a coherent clade within the d iverse group of Eimeria species. These findings raise important questions a bout the evolutionary relationships of the eimeriids and Cyc-hu host range and should lead to improved polymerase chain reaction-based diagnostics.