Prevalence and molecular characterization of novel species of the Diplomonad genus Octomitus (Diplomonadida: Giardiinae) from wildlife in a New York watershed

Octomitus is a diplomonad genus known to inhabit the intestinal tracts of rodents. Ultrastructural morphology and 18S rDNA gene sequence analysis support the placement of Octomitus as the closest sister lineage to Giardia, a parasite which causes diarrheal disease in humans and animals worldwide. However, further information on the ecology and diversity of Octomitus is currently scarce. Expanding the available database of characterized sequences for this organism would therefore be helpful to studies of Diplomonad ecology, evolution, and epidemiology, particularly related to the evolution of parasitism in Giardia and Spironucleus, another related Diplomonad common in commercial fish farming. In order to study the prevalence and genotypic diversity of Octomitus, we developed a nested PCR assay specific to Octomitus and optimized to detect genotypes in fecal samples collected from wildlife in a New York watershed, and sequenced a portion of the small subunit ribosomal DNA (18S rDNA) gene to identify samples to species level. Molecular evidence suggested that Octomitus genotypes display similar prevalence to Cryptosporidium and microsporidian pathogens in wildlife as well as strong host preference for rodent and opossum hosts. Phylogenetic analysis showed strong support for 14 Octomitus genotypes, 13 of these novel, and patterns of host-parasite co-evolution.