Presumptive synchronized nuclear divisions without cytokinesis in the Rhinosporidium seeberi parasitic life cycle

Abstract

Despite numerous studies of the Rhinosporidum seeberi parasitic phase, the stages of its nuclear cycle leading to the formation of endoconidia have yet to be properly described. R. seeberi resists culture and can only be investigated on histological preparations. We have evaluated tissue sections collected from 35 host species with rhinosporidosis searching for the presence of mitotic figures during sporangia development. This study found that soon after endoconidia release, the prominent reddish vesicles typical of this stage vanished leading to the development of juvenile sporangia (JS) 12-70 mm in diameter. This stage possesses granular cytoplasm, a thick cell wall, and a central reddish nucleus with a conspicuous nucleolus. The first nuclear division takes place in the JS. It is a rarely encountered event characterized by the development of a distorted nucleus leading to the formation of two nuclei without cytokinesis. The finding of multiple nuclear divisions at prophase-, metaphase-and telophase-like stages without cytokinesis was detected in intermediate sporangia (IS). IS with multiple dividing nuclei seem to be at the same stage of nuclear partitioning, suggesting synchronized nuclear division. In these sporangia, the nuclei continue divisions without cytokinesis until the sporangia reach ¢300 mm in diameter. The last nuclear division prior to cytokinesis appears to take place in very large sporangia with thousands of nuclei. The build-up of cytoplasm around each nucleus and the formation of a thin cell wall lead to the formation of endoconidia. This study revealed the presence of several mechanisms of pathogenesis in R. seeberi that deserved further investigation.

Rhinosporidiosis in the Americas: A Systematic Review of Native Cases

“…Reports of rhinosporidiosis in dry areas of Sri Lanka suggest R. seeberi can survive in these types of environments and be infective. 9,11,22 The presumed mode of infection is the contact of a disrupted epithelial layer with water or dust containing R. seeberi. Similar to what is reported in India, most of the cases in this review lived in cities with rivers or lakes in the vicinity, where people usually bathe.…”

What is your diagnosis? Ulcerative nasal lesion in a Quarter Horse

“…Cytologic features have been described and the morphology of the mature endospore is distinctive; the dark pink globules differentiate it from typical fungal yeast . Histopathologic findings were supportive of the cytologic diagnosis in this case, although sporangia were rare and limited to juvenile forms . Definitive confirmation can be achieved using PCR, but an appropriate sample was not available in this case.…”