Rhinosporidium seeberi

Rhinosporidium seeberi is a eukaryotic pathogen responsible for rhinosporidiosis, a disease which affects humans, horses, dogs, and to a lesser extent cattle, cats, foxes, and birds. It is most commonly found in tropical areas, especially India and Sri Lanka.

The pathogen was first identified in 1892, and was comprehensively described in 1900 by Seeber.

Many aspects of the disease and of the pathogen Rhinosporidium seeberi remain problematic and enigmatic. These include the pathogen’s natural habitat, some aspects of its ‘lifecycle’, its immunology, some aspects of the epidemiology of the disease in humans and in animals, the reasons for the delay at in vitro culture, and establishment of disease in experimental animals, hence paucity of information on its sensitivity to drugs, and the immunology of the pathogen. Thankamani isolated an organism believed to be R. seeberi and gave the name "UMH.48." It was originally isolated from the biopsies and nasal swabs of rhinosporidiosis patients. The various developmental stages of UMH.48 showed a strong resemblance with the structures seen in hisopathological sections of rhinosporidiosis in tissue samples. The spores of UMH.48 were found to be viable even after a decade of preservation in the refrigerator without any subculture, resembling the features of Synchytrium endobioticum, a lower aquatic fungus that causes black wart disease in potatoes. However, carefully performed molecular studies showed the definitive identity of the organism.

Phylogeny

For most of the 20th century, the classification of R. seeberi was unclear (being considered either a fungus or a protist), but it was shown to be part of a group called the Mesomycetozoea (or "DRIP clade"), which includes a number of well-known fish pathogens such as Dermocystidium and Sphaerothecum destruens.