Fungal Disease of the Equine Nasal Passages

Dr. Alison Hanson

Dr. Daniel J. Burba

When a mass is discovered in an equine nasal passage, fungal disease must be considered. However, as compared with other diseases, fungal disease of the equine upper respiratory tract is rare.  The lesions of fungal disease often appear as “granulomas”, or nodular, firm, persistent masses.

            There are several different types of equine nasal fungal disease.  Phycomycosis refers to infections caused by Pythium insidiosum, Basidiobolus haptosporus, or Conidiobolus coronatus. Only Conidiobolus coronatus has a predilection for the equine nasal passages.  The disease is seen primarily in subtropical and tropical parts of the world. Most cases seen in the United States cases originate from the swampy, hot climates of Texas or Louisiana.  The organism is an inhabitant of soil and rotting vegetation.  The organism prefers the skin of the nostrils and membranes of the nasal passages, but may also cause lesions in the throat.  The lesions are called "leeches" and/or "kunkers" because they are hard, pale gray to yellow, ulcerated, and elongated in shape.

Phycomycosis of the nostrils/nasal passages or “rhinophycomycosis” can grow large enough to block the airway.  The lesions referred to as granulomas can often be seen protruding from the nostril and septum with ulcerated surfaces.  These masses can be extremely itchy and the horse may constantly try to scratch his nose.  The masses may expand into the oral cavity possibly distorting the lips and impairing eating.  A veterinarian can diagnose rhinophycomycosis based on appearance and a biopsy. 

Treatment options vary depending on the extent of involvement. Complete surgical excision using a laser and post-surgical topical application of an antifungal medication is one therapy.  As an alternative to surgery, or when surgical removal is not complete, antifungal medication may be injected into the mass(es).  Recurrence is not uncommon.  The disease in some cases may be too advanced for treatment to be successful by the time the diagnosis is made.

            Another fungal infection is Cryptococcosis. It is a rare disease caused by Cryptococcus neoformans, a yeast-like organism that lives in barnyard soil and manure.  The nasal sinuses are most commonly affected in horses, with extension into the brain possible.  These infections are chronic, or long-standing.  If visible, the granulomas (lesions) can be recognized as large, lobulated, firm swellings.  Sinus lesions can cause erosion and distortion of the bones of sinus walls and nasal septum.  Granulomas in the nasal cavity cause foul-smelling, pus-and-blood-tinged nasal discharge often confined to one nostril.  Difficulty breathing may be seen. 

            Timely diagnosis is important because cryptococcosis can be spread to humans.  Diagnosis is made by biopsy and special staining.  Identification of the organism on a culture can also be diagnostic.  X-ray imaging may reveal smooth, well-demarcated masses in the nasal passages and sinuses. 

Treatment may include antifungal medications such as amphotericin B or fluconazole, although the infection may be too advanced to treat by the time it is diagnosed.  Cryotherapy (freezing) is another possible treatment but thorough investigation of long-term effects or efficacy in horses is lacking.

            Another fungal infection, Coccidioidomycosis, is caused by Coccidioides immitis, an organism that lives in the soil, particularly in the Southwestern United States and in South America.  The disease can be distributed throughout the body, or it can be localized to the nasal cavity, as is the case in most equine patients. As with most fungal infections it may cause mucus, pus, and/or bleeding from the nose.  In addition, exercise intolerance and abnormal respiratory noise are not uncommon.  A veterinarian may need the aid of an endoscope to make the diagnosis because the granulomas are most commonly found far back in the nasal passages.  These masses are smooth-walled and glistening and protrude into the nasal passages.  The masses can be visualized with x-ray.  Biopsy again can confirm the diagnosis.  Surgical (i.e. laser) removal of the granulomas is the treatment of choice.  Even after surgical removal, recurrence at different sites has been known to take place.  Oral fluconazole may offer an alternative therapy.

Aspergillosis is caused by Aspergillus fumigatus.  This fungus forms "plaques" in the sinuses.  Signs of disease are foul-smelling nasal discharge and possibly intermittent nasal bleeding and enlargement of the lymph nodes under the lower jaw.  Even with an endoscope, the lesions are so far up in the sinus "recesses", diagnosis may be difficult.  If diseased tissue can be obtained through the endoscope, a biopsy diagnosis can be made; if not, the organism may be identified on a culture or smear of the nasal discharge.

Topical natamycin infused through the endoscope or nystatin powder dusted into the affected nasal passage for three to eleven days is an effective treatment.  This procedure can be enhanced by removal of the plaque with the biopsy instrument of the endoscope or laser fiber before applying the medication.  Other drugs that may be effective are amphotericin B, miconazole, and fluconazole.

Rhinosporidiosis is caused by Rhinosporidium seeberi.  This "fungus" is considered as such because of its appearance. It is found in the southern United States, including Louisiana, and in other tropical countries.  The disease is rare in the horse.  One or several attached or free small "polyps" can be seen at the opening of the nostril, around the nasal septum, or on the edges of the eyes.  The horse rarely has other signs of disease.  Diagnosis is based on examination of biopsy specimens.  Surgical removal of the polyps is the treatment of choice but recurrence is frequent if the polyps are incompletely removed.

Lastly, a "mycetoma" is an infection characterized by lobulated masses, abscesses, and draining tracts that is caused by the "higher order of fungi".  Multiple or single lesions can be seen. The lesions develop on the skin and mucous membranes of the mouth, nose, and eyes.  It is thought that a wound or repeated irritation to the skin initiates the infection.  One causative organism of nasal sinus mycetoma is Pseudoallescheria boydii; this organism also causes human mycetoma.  Signs of disease are nasal discharge containing mucus and pus and nasal bleeding.  A biopsy of the lesion with the aid of endoscopy is necessary for diagnosis. Culture of the organism is also attempted.  Surgical removal of the mass followed by topical treatment with a drug effective against the organism involved is recommended.

In summary, several types of fungi may infect the equine nasal passages. It is important to remember that fungal disease of the equine upper respiratory tract on the whole is rare.  If any sort of mass is noticed anywhere on or in the nostrils or nasal passages, a veterinarian should be contacted immediately, because prompt treatment of fungal disease in these areas may make a significant difference in the overall outcome.  Once fungal disease has spread into the sinuses, treatment becomes much more frustrating and recurrence is likely.