Molecular Evidence for Multiple Host-Specific Strains in the Genus Rhinosporidium

Abstract

The taxonomic relationship of Rhinosporidium seeberi with other organisms remained controversial for over a century. Recently, molecular studies have shown R. seeberi to be a protistal microbe in the newly described class Mesomycetozoea at the animal-fungal boundary. Phylogenetic analyses of R. seeberi using 18S smallsubunit (SSU) rRNA genes from several hosts suggested Rhinosporidium as a monotypic genus. To test this hypothesis, the internal transcribed spacer 1 (ITS1), 5.8S, and ITS2 from eight humans, two swans, and a dog with rhinosporidiosis were sequenced. The ITS regions were amplified by PCR using a primer designed from a unique region of R. seeberi's 18S SSU rRNA genes in combination with the ITS4 universal primer. In addition, the universal ITS4 and ITS5 primers were also used. R. seeberi's ITS sequences showed differences in the numbers of nucleotides among strains. For instance, the eight human ITS sequences were uniformly similar with only a few mismatches and ϳ1,060 bp long. In contrast, sequences from one of the swans and the dog were 1,356 bp and ϳ1,147 bp long, respectively. Clustal analysis of all of the ITS sequences showed multiple 50-to 60-bp gaps and several mismatches among them. Parsimony analysis placed the Rhinosporidium ITS sequences in three well-supported sister groups according to the hosts' identities. This analysis strongly suggests that the genus Rhinosporidium may possess multiple host-specific strains. No correlation was found between this finding and the phenotypic features of R. seeberi in the studied samples.Rhinosporidiosis is a cutaneous and/or subcutaneous chronic disease of human and other animals caused by Rhinosporidium seeberi (2,(16)(17)(18). This granulomatous disease is characterized by the development of polyps primarily affecting the mucous membranes of the nostrils and the ocular conjunctivae of the infected hosts. Diagnosis is essentially based on the histological detection in tissues of R. seeberi's pathognomonic endosporulating sporangia in various stages of development. Rhinosporidiosis in not a life-threatening disease, and its treatment usually is limited to the surgical removal of the polyps (1, 4, 11).For the last 100 years, the taxonomic affinities of R. seeberi remained obscure, principally because this unique pathogen cannot be cultured. Thus, most of its epidemiological and taxonomical characteristics were not well understood. In 1999, a team from the United States and Sri Lanka (10) using molecular tools found that R. seeberi was phylogenetically related to a novel group of protistan microbes at the divergence between animals and fungi. This finding was soon corroborated by others (8). These microbes are presently classified in the protistal class Mesomycetozoeae. R. seeberi shares several characteristics with the other members of this class; all are aquatic microbes with spherical structures containing endospores. Most of them are unculturable and were, at one point, classified as members of the fungal or protistan kingdoms.The studies of Herr et ...

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

“…Conversely, some histochemical analyses found that these vesicles contain lipidic and proteinaceous elements (Arseculeratne, 2002;Bader & Grueber, 1970;Vanbreuseghem, 1973), a finding that agrees with the position of Ashworth (1924) and Easley et al (1986). Furthermore, our data and other studies showed that the nuclei of R. seeberi are~2-4 mm in diameter (Easley et al, 1986;Thianprasit & Thagerngpol, 1989;Kennedy et al, 1995;Pereira et al, 2005;Savino & Margo, 1983;Vanbreuseghem, 1973;Vilela & Mendoza, 2012), thus the presence of a nucleus inside a 0.5-3.0 mm-diameter vesicle is highly questionable. Besides, there is not a single example of a eukaryotic pathogen releasing their nucleated progeny without a protective cell wall.…”

“…According to our observations and those recorded by others (Ashworth, 1924;Kannan-Kutty & Teh, 1974Kennedy et al, 1995;Mendoza et al, 2002;Thianprasit & Thagerngpol, 1989;Vanbreuseghem, 1973), each endoconidium possesses a single nucleus and maintains its cell wall integrity at all times (Pereira et al, 2005;Vilela & Mendoza, 2012), a concept that is in sharp contrast with the spore-morulae hypothesis. Conversely, believe that the concentric 0.5-1.5 mm diameter ring structures, also termed laminated bodies (LB) and frequently encountered in EM preparations, are involved in the development of endoconidia.…”

“…Although the early photographic documentation published in the first part of the 20th century suggested that R. seeberi was a typical eukaryotic microbe with complex stages of its nuclear cycle (Acevedo, 1958;Ashworth, 1924;Kurunaratne, 1964), these observations were conveniently overlooked by the studies of the last 40 years (Apple, 1983;Arseculeratne, 2002;Bader & Grueber, 1970;Easley et al, 1986;Herr et al, 1999b;Kannan-Kutty & Teh, 1974Kennedy et al, 1995;Savino & Margo, 1983;Silva et al, 2005;Teh, 1974;Thianprasit & Thagerngpol, 1989;Vanbreuseghem, 1973). Ashworth (1924) described for the first time in R. seeberi the stages of the nuclear cycle during prophase, metaphase, anaphase and telophase.…”

“…Within the 35 host tissue samples, two specimens, also studied by Herr et al (1999a, b) and Silva et al (2005), containing R. seeberi mitotic structures were also processed for EM. In brief, the samples were fixed in 2.5 % glutaraldehyde with 0.05 M sodium cacodylate-buffered saline (pH 7.4) at room temperature for 2 h, followed by three washes with the same reagent for 20 min each.…”

Overview of Zoonotic Diseases in Turkey: The One Health Concept and Future Threats

“…The etiologic pathogen organism causes similar infections in amphibians and fish (414). Another molecular work has demonstrated evidence that R. seeberi may have host-specific strains (eg, human vs dog versus swan) (415). Humans generally acquire the infection by contact of the nasal mucosa with infectious material when bathing in ponds contaminated by animal feces (416).…”