Rhinosporidium seeberi: Is It a Fungi or Parasite?

Rhinosporidium seeberi (R. seeberi) causes rhinosporidiosis, which is manifested as tumor-like polyps developing primarily in the nostrils and conjunctiva in human and animals. This disease is characterized by the presence of large, round-shaped mature stage and small endospores with resistance to culturing. R. seeberi was first reported in 1900 as a sporozoan parasite, but later classified as a lower fungi, although its morphological similarity with aquatic parasites were also noticed. According to 18S small-subunit ribosomal DNA sequencing, R. seeberi belongs to a group of fish parasite DRIP clade located between the animal and fungal divergence. Histological examination is thus necessary for the definitive diagnosis of rhinosporidiosis, and the first line of treatment is usually total surgical excision and electro-cauterization of the polyp base. Among the drug therapies attempted, remission has been reported in some patients who received only Dapson treatment. This disease is endemic across India, Pakistan and Sri Lanka and occurs sporadically in other parts of The World with a common history of patients bathing in stagnant water. An outbreak in Serbia during 1992-1995 and 5 rhinosporidiosis cases from Turkey have been reported until date. Considering that rhinosporidiosis is associated with exposure to water and the agent belongs to a branch of aquatic parasites, it has been proposed that aquatic animals are the natural hosts and that the mammalian hosts acquire infection by contacting contaminated water. Therefore, there is a need for the investigation of the infection in fish besides mammalian animals as reservoirs as well as to conduct screening of antiparasitic drugs with infected fish or infected cell lines with the nearest phylogenetic relatives of R. seeberi.