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Disease Entity

Rhinosporidiosis (also known as Rhinosporidiosis of mucosal membranes, Conjunctival Rhinosporidiosis, “water mold”).


Rhinosporidiosis is a rare, infectious, chronic granulomatous disease caused by Rhinosporidium seeberi, an endosporulating microorganism. It has recently been classified in the taxonomic group, mesomycetozoea, which is a group of microorganisms at the boundary between fish and fungi. The disease is most prevalent in warm, tropical climates, with over 90% of cases found in the Indian subcontinent. The nose and nasopharynx are most commonly involved at over 70% of reported cases, with ocular manifestations accounting for 15% of cases.[1][2]

Clinical presentation of rhinosporidiosis depends on the location of the lesion and is typically found in mucosal membranes. The most common site of ocular lesions is the conjunctiva and lacrimal sac. Conjunctival rhinosporidiosis can be flat or pedunculated, depending on which area of the conjunctiva is involved and if there is space to grow. More uncommon sites include the lip, palate, maxillary antrum, uvula, epiglottis, larynx, trachea, bronchus, ear, vulva, penis, rectum, and scalp. In the rare occasion of a disseminated infection, limbs, trunks, viscera and brain can be involved, with brain involvement often leading to fatalities. According to Sinha et. al, there have been more reported male cases compared to females, but the difference is minimal (57% to 43%), with the majority of cases involving young adults. The younger age groups may be at risk due to the likelihood of young adults working outdoors or participating in outdoor activities.[2][3]


Rhinosporidiosis is an infection endemic to India, Sri Lanka, and Pakistan, Africa, and South America. It can also result from sporadic cases around the world. Rhinosporidiosis is caused by R. seeberi, which epidemiological evidence has found predominantly in stagnant water sources in tropical climates. Human-to-human transmission has not been identified, and therefore the disease is not considered contagious. Cases have also been reported in several species of farm, domestic, and wild animals such as dogs, cats, horses, cattle, ducks and swans.[2][3][4][5]

The first reported case of rhinosporidiosis was in 1900 by Guillermo Seeber from Buenos Aires, who described a highly vascular nasal polyp. At that time the infectious agent was thought to be fungus and the classification of the species has been under debate for many years. In 1923, Asworth described the established the nomenclature, Rhinosporidium seeberi, after describing its life cycle.[2][4]

Risk Factors

  • Living near, or visiting a warm, tropical climate
  • Endemic regions such as India, Pakistan, Sri Lanka, African continent
  • Swimming or working near a stagnant water source (paddy workers, river-sand workers)
  • Traumatized epithelium with Rhinosporidium exposure (by water or air)
  • Inhalation of field dust contaminated by spores in feces of infected animals


General Pathology

The pathology of Rhinosporidiosis stems from an infection from R. Seeberi, resulting in a highly vascular, often pedunculated soft tissue mass located in mucosal tissue such as nasopharynx, conjunctiva, and lacrimal sac.


Rhinosporidiosis is an infectious, highly vascular, polypoidal, soft tissue mass. It is caused by inoculation into a break of skin or from inhalation of Rhinosporidium seeberi. The reservoir for R. seeberi is stagnant water and soil. Despite being first identified in 1900, its classification has been under dispute due to its overlapping characteristics with fungi, fish, and amphibian pathogens. Human infection in the majority of reported cases is through contact of contaminated water with epithelial injury on the skin. The highest incidence of cases reported in river-sand workers.[2]

Rhinosporidium seeberi is an infectious organism that is intractable to isolation and cannot be grown in artificial media. The microorganism can maintain its life cycle in tissue culture. Most reported cases show an association of rhinosporidiosis occurring in individuals in contact with stagnant, contaminated water. The infection occurs from inoculation of a site with R. seeberi in the form of endospores. These endospores develop into juvenile sporangia called trophocytes that do not contain any endospores. These trophocytes are 10-100 microns large, with a single layer of cells forming the cell wall. Trophocytes mature into intermediate sporangia which are larger, with thicker, bilamellar walls. Intermediate sporangia grow into mature sporangia, which are approximately 100-300 microns thick, filled with a large number of endospores, and surrounded by immune cells. Water or watery substance stimulates the endospores to be released from the sporangia perpetuating the infection and life cycle. After initial infection with R. seeberi, replication occurs rapidly in the mucosa at the site of infection with hyperplasia of host tissue and recruitment of local immune response to develop the lesion. This immune response to the infection leads to the formation of a granuloma and further develops into a multilobulated mass at the site of infection.[8]

Primary prevention

Primary prevention is to avoid swimming in stagnant water, particularly in warm, tropical climates, or endemic regions.


Histopathology is the definitive way to confirm a diagnosis of Rhinosporidiosis, . On histopathology, visible trophocytes and sporangia will be in different stages of development with surrounding infiltration of inflammatory cells and hyperplasia of the mucosal tissue.[2]


Patients presenting with rhinosporidiosis may often have a history of swimming in stagnant water, have recent travel or residence in endemic areas, work near rivers or are river-sand workers.[2][5][6]

Physical Examination

Rhinosporidiosis occurs when the endospores of R. seeberi infect the mucosa through a traumatized epithelium, leading to hyperplasia and growth of a soft lesion on the site of infection. It can present in various locations in the body, but predominantly arise in the nasal passage, eyes and oropharynx. Rhinosporidium polyps appear as a soft tissue lesion that is granular, fleshy, and red in color with multiple yellowish to white pin head sized dots that indicate underlying mature sporangia. Depending on the location, the lesion can present as pedunculated or flat.

In Sinha et al, nasopharyngeal lesions are described as often being multi-lobed and less vascular. Patients often complain of epistaxis, nasal obstruction, rhinorrhea, anosmia. Conjunctival rhinosporidiosis presents with a similarly fleshy lesion, which can be pedunculated if formed in palpebral conjunctiva or flat if formed in the bulbar conjunctiva. Bulbar conjunctival lesions are typically sessile and flat as the lids over the conjunctiva exert a flattening force. Patients present with symptoms of watery eyes, conjunctivitis, photophobia. If the lacrimal sac is involved, bloody tears may be present.


  • Pedunculated, or flat sessile soft tissue growth
  • Fleshy appearance
  • Pinpoint white or yellow spots
  • Highly vascular and friable with free bleeding
  • Proptosis



  • Watering of eyes (ocular lesion)
  • Conjunctivitis (ocular lesion)
  • Bloody Tears (ocular lesion)
  • Photophobia (ocular lesion)
  • Itching (ocular and nasopharynx lesion)
  • Difficulty breathing (nasopharynx lesion)
  • Rhinorrhea (nasopharynx lesion)
  • Anosmia (nasopharynx lesion)
  • Epistaxis (nasopharynx lesion)
  • Difficulty swallowing (oropharynx lesion)


Diagnostic procedures

Definitive diagnosis of rhinosporidiosis depends on histological examination with immunohistochemistry. This often requires excisional biopsy, scraping of superficial lesions or fine needle aspiration. The histopathological sections will show sporangia in multiple stages of maturation enclosed within a thin wall. The sporangia can range from 50-1000 μm in diameter with endospores inside that are approximately 5-10 μm. The overlying and surrounding tissue has rapid growth with the infection with hyperplasia of the tissue and loose fibrovascular stroma. Immune reactions to the infection also results in infiltration with lymphocytes, macrophages, plasma cells and PMNs.[5] Rupture of the sporangia can result in a giant cell reaction. Despite having overlapping characteristics with fungi, R. seeberi lacks the Splendore-Hoeppli reaction, which is characterized by an eosinophilic infiltration. A key characteristic of rhinosporidiosis is that the infected site is almost completely devoid of eosinophils.

Multiple stains can assist in the diagnosis of rhinosporidiosis. The sporangia and endospores stain positively to various special stains such as Mucicarmine, Gomori’s methenamine-silver, PAS, etc. Nasopharyngeal polyps are the most commonly infected sites, and identification of endospores is often difficult when compared to epithelial cells of the respiratory sites. Periodic Acid Schiff (PAS) staining is helpful to use as endospores are PAS positive, but PAS negative in epithelial cells. Mucicarmine stain can be helpful in distinguishing R. Seeberi (stains positively) from Coccidiodes immitis (does not stain positively). Furthermore, cytologically, coccidiomycotic lesions can often look similar to rhinosporidial lesions as both are represented by large, thick- sporangia containing small endospores. However, using H and E staining can show that R. seeberi endospores are larger and more numerous than C. immitis.[2][5]

Differential diagnosis

  • Pyogenic granuloma
  • Squamous or conjunctival papilloma
  • Hemangioma
  • Arteriovenous malformation
  • Chronic infection
  • Oncocytoma
  • Sebaceous adenoma
  • Squamous carcinoma
  • Foreign body
  • Conjunctival cyst
  • Inflamed pinguecula



Rhinosporidiosis infection is treated primarily with surgical intervention. Medical management has rarely been reported as adjunct treatment to surgery.

General treatment

Th first line treatment of rhinosporidiosis is surgical, and the method utilized is dictated by the location of the lesion. In the majority of cases, total surgical excision is completed using cautery. Electrocautery minimizes the bleeding from the highly vascular structure and limits the release of endospores into the nearby mucosa. This may decrease the chance of recurrence.

Medical treatment with Dapsone and Amphotericin B is possible, but not well studied. Efficacy of these drugs are controversial, but may be used in disseminated disease. Dapsone has been used in a few case reports but always as an adjunct to surgical treatment. As R. seeberi cannot be grown in vitro, drug sensitivities are currently unknown.[2][5]

Medical therapy

Medical management of rhinosporidiosis has not been strongly advised in reported cases. Currently, dapsone is an adjuvant drug to surgery.[2][6]


Total excision of the polyp or conjunctiva is recommended, and electrocautery is most commonly utilized as it restricts free bleeding. If there is lacrimal sac involvement, a dacryocystectomy is typically done. The procedure should remove the entirety of the entire sac, and post-operative Dapsone therapy is usually recommended. In a retrospective case series from India, 65% of all patients with lacrimal sac involvement had localized disease.[10] During removal of the polyp, spillage of the endospores into the surrounding mucosa may occur which can be contained by electrocautery.[2][6]


Complications of rhinosporidiosis are relatively rare. Disseminated infection may occur leading to osteolytic bone lesions which may be difficult to distinguish from relapse or reinfection in endemic regions[5]. Disseminated infection of the limbs can lead to bone destruction or infection of the brain and other sites of the body. It is difficult to treat and can lead to increased morbidity. In addition, local secondary bacterial infections are significant complications that can lead to morbidity as well. Recurrence rates of ocular rhinosporidiosis is lower than that of nasopharyngeal rhinosporidiosis.[2][3]


Despite the rare case of recurrence, regeneration or dissemination, the prognosis is generally very favorable. It typically follows a benign, prolonged course without treatment with limited morbidity. Morbidity is typically associated when there is a secondary infection or dissemination occurs.


  1. Mendoza L, Taylor JW, Ajello L. The class mesomycetozoea: a heterogeneous group of microorganisms at the animal-fungal boundary. Annual review of microbiology. https://www.ncbi.nlm.nih.gov/pubmed/12142489. Published 2002. Accessed August 20, 2019.
  2. 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 2.12 2.13 Sinha A, Phukan JP, Bandyopadhyay G, et al. Clinicopathological study of rhinosporidiosis with special reference to cytodiagnosis. Journal of cytology. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3543593/. Published October 2012. Accessed August 20, 2019.
  3. 3.0 3.1 3.2 Vukovic Z, Bobic-Radovanovic A, Latkovic Z, Radovanovic Z. An epidemiological investigation of the first outbreak of rhinosporidiosis in Europe. The Journal of tropical medicine and hygiene. https://www.ncbi.nlm.nih.gov/pubmed/7563262?dopt=Abstract. Published October 1995. Accessed August 20, 2019.
  4. 4.0 4.1 Thakur SKD, Sah SP, Badhu BP. Oculosporidiosis in eastern Nepal: a report of five cases. The Southeast Asian journal of tropical medicine and public health. https://www.ncbi.nlm.nih.gov/pubmed/12236438. Published June 2002. Accessed August 20, 2019.
  5. 5.0 5.1 5.2 5.3 5.4 5.5 5.6 5.7 Morelli L, Polce M, Piscioli F, et al. Human nasal rhinosporidiosis: an Italian case report. Diagnostic Pathology. https://diagnosticpathology.biomedcentral.com/articles/10.1186/1746-1596-1-25. Published August 31, 2006. Accessed August 20, 2019.
  6. 6.0 6.1 6.2 6.3 6.4 Nair AG, Ali MJ, Kaliki S, Naik MN. Rhinosporidiosis of the tarsal conjunctiva. Indian journal of ophthalmology. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4501149/. Published May 2015. Accessed August 20, 2019.
  7. Prasad V, Shenoy VS, Rao RA, Kamath PM, Rao KS. Rhinosporidiosis: A Chronic Tropical Disease in Lateral Pharyngeal Wall. Journal of clinical and diagnostic research : JCDR. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4484095/. Published May 2015. Accessed August 21, 2019.
  8. Morphology & Incubation Period. Morphology. https://web.stanford.edu/group/parasites/ParaSites2002/rhinosporidiosis/morphology.htm. Accessed August 20, 2019.
  9. Reddy AK, McAllister AR, Syed NA, Allen RC. Conjunctival rhinosporidiosis in a temperate climate. EyeRounds.org. https://webeye.ophth.uiowa.edu/eyeforum/cases/224-rhinosporidiosis.htm. Published November 3, 2015. Accessed August 20, 2019.
  10. Behera S, Chowdhury RK, Dora J. Rhinosporidiosis of the lacrimal sac in a tertiary care hospital of India - A retrospective case study. Indian J Ophthalmol. 2022 May;70(5):1732-1735. doi: 10.4103/ijo.IJO_2890_21. PMID: 35502062; PMCID: PMC9332973.
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