Recent advances in rhinosporidiosis and Rhinosporidium seeberi.

Rhinosporidiosis and its causative pathogen Rhinosporidium seeberi have been known for over a hundred years. Yet unresolved enigmas in rhinosporidiosis include the mode of infection, mechanisms of spread, mechanisms of immunity, some aspects of histopathology e.g. the significance of transepidermal elimination of sporangia, the cause of the variation in cell infiltration patterns in rhinosporidial tissues and their correlations with immune status, and the absence of the Splendore-Hoeppli reaction which is well-marked in invasive, classical mycoses. This review describes the main features of rhinosporidiosis and discusses recent work which clarifies some of these enigmas. Recent work included in this review are molecular biological classification of R. seeberi among the hydrophilic organisms of the former DRIP clade, establishment of a method for the purification of the developmental stages, and some aspects of the immunology of R. seeberi with reference to mechanisms of immune evasion - antigenic variation, host immunoglobulin binding, immune deviation in relation to the chronicity, recurrence and dissemination seen in rhinosporidiosis. The mechanism of endospore release from the sporangium has been described. Some problems involved in the resolution of enigmas that persist are briefly discussed.