Rhinosporidiosis

Rhinosporidiosis is an infectious disease which occurs in the New Wold, Europe, Africa and Asia, but is most common in the tropics (India and Sri Lanka). The disease was first described in Argentina around 1890 by Malbran and Guillermo Seeber (the subject of his thesis). The disease is characterised by slow-growing, painless polyps or tumour-like masses, which are usually found on the nasal mucosa, lachrymal sac, conjunctivae, palate, larynx or penis. Chronic rhinitis and/or epistaxis may occur. Disseminated infections with lesions of skin, liver, spleen and kidneys, are very rare. Treatment consists of surgical excision, but recurrence can be expected in approximately 10% of patients. Biopsy shows a characteristic picture of large (up to 300 microns) spherical thick-walled cysts, containing hundreds or thousands of endospores measuring 7-9 µm. Around the cysts there is an inflammatory infiltrate with neutrophils and small abscesses. The protozoon may be detected by staining with silver (methenamine), PAS [periodic acid-Schiff] or mucicarmine after KOH digestion of the specimen. Rhinosporidium seeberi has not to date been cultured in vitro. This species is a eukaryote and is difficult to classify, having the properties of both fungi and protozoa.

A few years ago the species was classified under Mesomycetozoa (a cladistic group). Recently, it has been shown, using PCR [polymerase chain reaction], that the protozoon is not closely related to the Eumycota. It also became apparent that R. seeberi is genetically close to the genus Dermocystidium as well as the “rosette agent” (pathogen of fish).

The name Ichthyosporea was proposed for a new taxonomic group which would include these organisms. The group would be placed in a taxonomic tree close to the division of fungi and animals. No natural reservoir is known. It is also assumed that people become infected by swimming in fresh water lakes or rivers. It is likely that fish or other water creatures are the normal hosts. Swans can be infected. A related species, R. equi, can infect horses and cattle.

Category: Medicine Notes