In vitro studies on the mechanisms of endospore release by Rhinosporidium seeberi

Nasal Rhinosporidiosis: Clinical Presentation, Clinical Findings, and Outcome in Dogs

The purpose of this study was to describe the clinical presentation, imaging findings, and outcome in 10 dogs diagnosed with Rhinosporidium seeberi infections. Histopathology and cytology records were searched at a veterinary teaching hospital and a veterinary diagnostic laboratory to identify dogs with rhinosporidiosis. Medical records were reviewed for clinical, imaging, endoscopic, and surgical findings. Outcome was determined via evaluation of records and, where possible, telephone conversation with the primary care veterinarian and/or owner. Young to middle-aged large-breed dogs with an approximately equal sex distribution were represented. Unilateral signs predominated. Diagnosis was confirmed by histopathology in 9 cases, and cytology was diagnostic in only 1 of 3 cases. Histopathology was superior to cytology. Masses were soft tissue and contrast enhancing with no evidence of bony lysis on computed tomography (2 dogs). Direct or rhinoscopic (2 dogs) visualization revealed white to yellow pinpoint foci. Surgical resection (4 dogs) can result in long-term disease-free periods (up to 2659 days), although repeat surgery can be required. Dapsone was well tolerated in 1 dog, and relapse was not noted despite incomplete surgical resection (follow-up 749 days). Visualization of pale foci on a rostral intranasal mass in an endemic region should prompt consideration of rhinosporidiosis.

Case Report: Rhinosporidiosis, Case Report, and Literature Review

Rhinosporidiosis is caused by Rhinosporidium seeberi, a pathogen currently considered a fungus-like parasite of the eukaryotic group Mesomycetozoea. It is usually a benign condition, with slow growth of polypoid lesions, with involvement of the nose, nasopharynx, or eyes. The clinical characteristics of a painless, friable, polypoid mass, usually unilateral, can guide the diagnosis, but the gold standard for diagnosis is histopathological findings. This article reviews the epidemiology, pathobiology, clinical manifestations, diagnostic strategies, and treatment approach for rhinosporidiosis.

Developmental stages of Amphibiocystidium sp., a parasite from the Italian stream frog (Rana italica)

Amphibian parasites of the genus Amphibiocystidium are members of the class Ichthyosporea (=Mesomycetozoea), within the order Dermocystida. Most of the species in the Dermocystida fail to grow in ordinary culture media, so their life cycle has only been partially constructed by studies in host tissues. However, to date, there have been few reports on the life cycle of Amphibiocystidium parasites with respect to the developmental life stages of both Dermocystidium and Rhinosporidium parasites. In this study, we provide light and electron microscopic findings of developmental phenotypes of Amphibiocystidium sp., a parasite previously characterized in the Italian stream frog (Rana italica), which has caused an ongoing infection in a natural population of Central Italy. These phenotypes exhibited distinct morphological characteristics that were similar to A. ranae from the skin of R. temporaria, but showed histochemical properties particularly comparable with those of maturing phenotypes of Rhinosporidium seeberi, and compatible with fungal-like parasites. Therefore, for Amphibiocystidium sp. phenotypes, we suggest adopting the terminology used for maturing stages of R. seeberi, such as juvenile sporangia, early mature sporangia and mature sporangia. The characterization of these developmental stages will be useful to increase the understanding of the life cycle of parasites of the genus Amphibiocystidium and of the interactions with their amphibian hosts.

Cluster of Nasal Rhinosporidiosis, Eastern Province, Rwanda

We report 4 recent cases of nasal rhinosporidiosis in Rwanda. All patients were boys or young men living in the same district (Gatsibo District, Eastern Province), suggesting a reservoir in the area. The recent reemergence of rhinosporidiosis in Rwanda might reflect increased availability of diagnostic services rather than emerging disease.

Pathological and phylogenetic characterization ofAmphibiothecumsp. infection in an isolated amphibian (Lissotriton helveticus) population on the island of Rum (Scotland)

Outbreaks of cutaneous infectious disease in amphibians are increasingly being attributed to an overlooked group of fungal-like pathogens, the Dermocystids. During the last 10 years on the Isle of Rum, Scotland, palmate newts (Lissotriton helveticus) have been reportedly afflicted by unusual skin lesions. Here we present pathological and molecular findings confirming that the pathogen associated with these lesions is a novel organism of the order Dermocystida, and represents the first formally reported, and potentially lethal, case of amphibian Dermocystid infection in the UK. Whilst the gross pathology and the parasite cyst morphology were synonymous to those described in a study from infectedL. helveticusin France, we observed a more extreme clinical outcome on Rum involving severe subcutaneous oedema. Phylogenetic topologies supported synonymy between Dermocystid sequences from Rum and France and as well as their distinction fromAmphibiocystidiumspp. Phylogenetic analysis also suggested that the amphibian-infecting Dermocystids are not monophyletic. We conclude that theL. helveticus-infecting pathogen represents a single, novel species;Amphibiothecum meredithae.

Rhinosporidium seeberi Nuclear Cycle Activities Using Confocal Microscopy

Rhinosporidium seeberi is an uncultivated Ichthyosporean infecting animals, including humans. Recent studies suggested R. seeberi undergoes synchronized nuclear division without cytokinesis. We used confocal microscopy to investigate R. seeberi nuclear division cycles in formalin-fixed tissues stained with DAPI and phalloidin. We report that R. seeberi nuclei in juvenile and intermediary sporangia synchronously divided without cytokinesis. Intermediary sporangia display numerous 3-4 μm nuclei at different mitotic stages as well as a thick inner layer with strong affinity for phalloidin. Mature sporangia showed numerous 5-12 μm cell-walled endospores, each containing a 2-4 μm in diameter nucleus. Phalloidin did not bind to the inner layers of mature sporangia or endospores. The development of a "germinative zone" in the inner layer of mature sporangia containing hundreds of nuclei was also confirmed. This study establishes that during the R. seeberi life cycle synchronous nuclear divisions without cytokinesis takes place, resulting in the formation of thousands of nuclei. Cytokinesis, on the other hand, is a 1-time event and occurs in the latest stages of intermediate sporangia, after the formation of thousands of nuclei and just before mature sporangia development.

[A new case of rhinosporidiosis in Chile]

BACKGROUND

Rhinosporidiosis is a chronic, granulomatous, and non-contagious infection, in which highly vascularized polyps (mainly present in the nasal cavity) appear. These polyps usually bleed easily.

AIMS

To present the case of a 14 year-old male suffering from an obstruction and injury of the right nostril due to a polypoid shaped-lesion with a raspberry-like appearance.

METHODS

A wide surgery resection of the base of the lesion was performed, as well as a standard histopathology procedure, including microscopic analysis with haematoxylin-eosin and Grocott staining.

RESULTS AND CONCLUSIONS

The histopathology report indicated that the chronic inflammatory polyp was compatible with rhinosporidiosis.

Rhinosporidiosis: what is the cause?

PURPOSE OF REVIEW

Significant advances in knowledge on rhinosporidiosis and Rhinosporidium seeberi were made in 1999, 2000, 2003 and 2004. These advances are reviewed on account of the continuing sporadic occurrence of the disease universally, and because of the availability of new approaches that could resolve persisting enigmas of both the disease and its causative pathogen.

RECENT FINDINGS

R. seeberi, the pathogen that causes rhinosporidiosis, has been definitively classified using molecular biological tools in a new clade - the Mesomycetozoea, along with 10 parasitic and saprobic microbes. The controversial spherical bodies of the endospores have been shown to comprise both lipid/protein nutritive bodies and other spherical bodies that are metabolizing units that reduce MTT (3-[4,5-dimethyl-2-thiazolyl]-2,5-diphenyl-2H-tetrazolium bromide). This indicates the viability of these spherical bodies, provisionally identified as the electron dense bodies that have also been shown to contain nucleic acids. MTT reduction as an indicator of viability has been used to determine the sensitivity of rhinosporidial endospores to biocides, antimicrobial drugs, and to specific antibodies. Genetic heterogeneity has been identified in strains from humans and animals. Cell-mediated and humoral immune responses have been demonstrated in human patients and in mice. Several mechanisms of immune evasion by R. seeberi have been identified.

SUMMARY

These findings are applicable in both clinical and laboratory practice, while the basic advances have implications in further work on experimental pathogenicity, the biology of R. seeberi, and on the epidemiology and pathogenesis of rhinosporidiosis.

Lymphadenitis, trans-epidermal elimination and unusual histopathology in human rhinosporidiosis

From a study of rhinosporidial tissues of 64 human cases of ocular, urethral and nasopharyngeal disease, unusual histopathological features of 27 cases are described. Histopathological evidence of lymphadenitis in rhinosporidiosis is presented for the first time. The phenomenon of 'trans-epidermal elimination' of sporangia of the causative pathogen Rhinosporidium seeberi is illustrated and it is argued that this phenomenon is rather the pathogen's mechanism for endospore-dispersal than a non-specific defence reaction of the host as has previously been suggested. Other unusual appearances described include variations in the intensity and composition of the host-cell infiltrate in tissues from different patients and in different portions of the same tissue, pitfalls in histopathological diagnosis, and unusual appearances of the pathogen. Histopathological clues to the pathogenesis of rhinosporidiosis and mechanisms of anti-rhinosporidial immunity in the host are discussed, illustrating the probable occurrence of immunesuppressive reactions to account for the variations in the density and composition of the host-cell infiltrate and the state of the rhinosporidial sporangia--intact or degenerate--, relating these variations to the chronicity, recurrences and systemic dissemination of rhinosporidiosis.

The class mesomycetozoea: a heterogeneous group of microorganisms at the animal-fungal boundary

When the enigmatic fish pathogen, the rosette agent, was first found to be closely related to the choanoflagellates, no one anticipated finding a new group of organisms. Subsequently, a new group of microorganisms at the boundary between animals and fungi was reported. Several microbes with similar phylogenetic backgrounds were soon added to the group. Interestingly, these microbes had been considered to be fungi or protists. This novel phylogenetic group has been referred to as the DRIP clade (an acronym of the original members: Dermocystidium, rosette agent, Ichthyophonus, and Psorospermium), as the class Ichthyosporea, and more recently as the class Mesomycetozoea. Two orders have been described in the mesomycetozoeans: the Dermocystida and the Ichthyophonida. So far, all members in the order Dermocystida have been pathogens either of fish (Dermocystidium spp. and the rosette agent) or of mammals and birds (Rhinosporidium seeberi), and most produce uniflagellated zoospores. Fish pathogens also are found in the order Ichthyophonida, but so are saprotrophic microbes. The Ichthyophonida species do not produce flagellated cells, but many produce amoeba-like cells. This review provides descriptions of the genera that comprise the class Mesomycetozoea and highlights their morphological features, pathogenic roles, and phylogenetic relationships.