Rhinosporidium seeberi: A human pathogen from a novel group of aquatic protistan parasites

Rhinosporidium seeberi, a microorganism that can infect the mucosal surface s of humans and animals, has been classified as a fungus on the basis of mo rphologic and histochemical characteristics. Using consensus polymerase cha in reaction (PCR), we amplified a portion of the R. seeberi 18S rRNA gene d irectly from infected tissue. Analysis of the aligned sequence and inferenc e of phylogenetic relationships showed that R. seeberi is a protist from a novel clade of parasites that infect fish and amphibians. Fluorescence in s itu hybridization and R. seeberi-specific PGR showed that this unique 18S r RNA sequence is also present in other tissues infected with R. seeberi Our data support the R. seeberi phylogeny recently suggested by another group. R. seeberi is not a classic fungus, but rather the first known human pathog en from the DRIPs clade, a novel clade of aquatic protistan parasites (Icht hyosporea).