Rhinosporidiosis

Also known as

Rhinosporidium seeberi infection

Description

Rhinosporidiosis is a chronic, nonfatal infection of humans and animals. This infection occurs primarily in the nasal mucosa in cattle and horses, causing formation of large polyps or wart-like lesions in the posterior nares (the two openings at the back of the nasal passage between the nasal cavity and the throat).

The polyps tend to block the nasal passage and interfere with breathing, creating a loud snoring sound and a thick nasal discharge (sometimes bloody) from both nostrils. Even if the polyps go away after a time, they tend to recur.

This infection also occasionally affects the skin of horses, cattle, dogs, cats, and aquatic birds, and sometimes occurs in mucus membranes of the eyes and in the lining of the mouth or the vagina in females.

The disease has been reported in more than 70 countries and is seen most often in India, Africa, and South America and less commonly in North America.

Rhinosporidiosis is sometimes confused with other granulomatous lesions (masses of immune cells that form at sites of infection) of the nasal mucosa and skin, including aspergillosis (infection caused by a certain type of mold), entomophthoromycosis (a subcutaneous fungal infection that causes swellings), “nasal granuloma,” and cryptococcosis (another type of fungal infection).

The polyps also resemble nasal obstruction caused by the blood fluke Shistosoma nasalis, and also sometimes might be mistaken for chronic allergic rhinitis (inflammation of the mucous membranes inside the nose) seen in cattle and sheep.

Microscopic spherules (in the sporangia—tiny sacs where spores are formed)) of R. seeberi in biopsy specimens confirms the diagnosis.

Signs

• Pink to deep red polyps in the nose that resemble strawberries (that bleed easily)
• Loud breathing
• Thick nasal discharge

Cause

Rhinosporidiosis is a chronic condition that produces polyp-like lesions.  Thought to be caused by the fungus Rhinosporidium seeberi, no one has yet been able to culture the organism from tissue samples.

There has been some controversy regarding the causative agent of this condition, and scientists for a while thought it is was a eukaryotic (organism with a clearly defined nucleus) protozoan parasite, algae or fungi or prokaryotic blue green algae which classed it as a fungi.

Various researchers thought R. seeberi belong to the class Mesomycetozoea. This pathogen is so mysterious, however, that we still don’t know how it evades the immune system and gets started in the body tissues.

In recent years, the causative organism has been identified by genetic techniques as a member of the aquatic Protista (also called Potoctista) rather than a fungus. The Protoctista are a kingdom of simple eukaryotic organisms, usually composed of a single cell or a colony of similar cells. Protists live in water, in moist terrestrial habitats, and also as parasites in the bodies of multicellular eukaroytes.

Examples of protists include algae, amoebas, euglena, plasmodium, and slime molds. Protists that are capable of photosynthesis include various types of algae, diatoms, dinoflagellates, and euglena. These organisms are often unicellular but can form colonies

The organism is taxonomically somewhere between animals and fungi (which are technically plants) and is closely related to certain pathogens of fish. The organism is difficult or impossible to culture. There is some evidence that host-specific strains exist.

Rhinosporidium seeberi causes slow-growing tumor-like masses in the nasal cavity. Although the mode of transmission is not understood, this disease often occurs in association with contact with aquatic or marshy environments, such as stagnant water.

It is thought that spores are released into the environment, where they contact susceptible human and animal hosts. Spores may be introduced into tissues after trauma to the mucous membranes, where they form sporangia that produce new spores. Because this disease in humans also occurs in arid regions, airborne spore transmission in dusty conditions might be another possible mode of infection—inhaling contaminated dust.

These growths have good blood supply and can be attached to the body membranes with or without a stalk at their base.  Interestingly, 90% of infections involve the nose of male animals.

Prevention

There is no sure way to prevent this disease since the spores may be present in the environment—except perhaps to reduce swampy or dusty conditions.

Treatment

Surgical removal of polyps is the standard treatment, but recurrence is common. In some cases dapsone (an antibiotic used in treating leprosy and some other skin infections) has been used successfully. Amphotericin B and itraconazole (anti-fungal medications) have also been used for medical treatment but are generally not as effective as surgery.