Rhinosporidium seeberi

At a glance

Shape

In tissue: large thick-walled sporangia full of endospores

Type

Aquatic protist (Mesomycetozoea / Ichthyosporea), historically classified with the fungi

Stain

H&E, PAS, GMS and mucicarmine stain the sporangia

Size

Mature sporangia up to several hundred µm; endospores a few µm

Morphology

• Huge round sporangia, visible even at low power, packed with thousands of endospores.
• Smaller immature stages (trophocytes) with a thick wall.
• It has never been grown on artificial culture media.

Transmission

• Contact of the nasal or conjunctival mucosa with stagnant fresh water or soil, for example bathing in ponds and rivers.
• Minor trauma to the mucosa probably helps entry.
• Not spread from person to person.

Reservoir: Fresh water and possibly aquatic animals such as fish; also infects horses, dogs and cattle

Isolation precautions

What the care team adds to standard precautions.

• Standard

Life cycle

1. Endospores from water or soil reach the nasal or conjunctival mucosa.
2. Each endospore enlarges into a thick-walled trophocyte in the submucosa.
3. The trophocyte grows into a large sporangium as its nucleus divides many times.
4. The mature sporangium fills with thousands of endospores.
5. It ruptures through a pore and releases endospores that spread locally and cause new polyps.

Virulence factors

• Slow local growth that forms vascular, friable polyps.
• Endospores released into the tissue explain local spread and recurrence after surgery.
• Granulomatous and mixed inflammation around ruptured sporangia.

Diseases it causes

• Nasal rhinosporidiosis: a pink to red, strawberry-like, friable polyp with unilateral obstruction and epistaxis.
• Ocular rhinosporidiosis: a fleshy polyp of the conjunctiva or lacrimal sac.
• Rarely skin, genital or disseminated lesions.

Clinical picture

• Usually a young man from a rural area with unilateral nasal obstruction and bleeding.
• The polyp surface shows tiny white dots, which are the sporangia.
• It can look like an inverted papilloma or other benign nasal tumor.

Diagnosis

• Histopathology of the excised polyp is the definitive test: sporangia with endospores.
• Smear of the lesion can show endospores.
• Culture does not work; PCR is a research tool.

Treatment

Complete surgical excision, ideally endoscopic with cautery of the base, is the treatment. Drugs are not effective on their own; dapsone has been used after surgery to reduce recurrence. Recurrence occurs in a minority of patients.

Drug class only; doses and regimens are set by the clinician from the current guideline.

In Pharmacology:

• Dapsone

Prevention

• Avoiding bathing in stagnant ponds where cases occur.
• Careful complete excision to avoid seeding endospores.

Test yourself

Think of the answer, then tap the question to see it.

Add to my cards (4)

Connections

← Back to the group: Other fungi of clinical interest

Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: Rhinosporidium seeberi: A Human Pathogen from a Novel Group of Aquatic Protistan Parasites (Emerging Infectious Diseases (CDC), 2000); Diagnóstico diferencial de la rinosporidiosis: a propósito de un caso (Iatreia (Universidad de Antioquia), 2012).

Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake

Send

Representative model, for educational purposes only.