ABSTRACT
Since its –rst identi–cation in 1900, controversies on the identity, taxonomy, and structure of Rhinosporidium seeberi prevailed for many decades. It is a unique pathogen that still, after 118 years, has been unable, because of its in vitro uncultivability, to ful–ll Koch’s classical postulates on the microbial causes of disease. The question Rhinosporidiosis: what is the cause? was posed even as recently as 2005.1 Is it a fungus? If it was, Libero Ajello thought it was a bizarre fungus. Added to this confusion was its later misidenti–cation with the common water cyanobacterium Microcystis aeruginosa.2 It is useful to recapitulate three likely sources of errors that led to this misinterpretation: (i) the failure to delineate the chain of causal relationships, (ii) the inadequate appreciation of the logic of scienti–c inference, and (iii) the reliance on morphology alone to identify taxonomic relationships.
