Rhinosporidium spp

From Dog
Nasal polyp at surgery. Miliary white foci on surface are sporangia of Rhinosporidiutii seeberi[1]
Mature spore from a sporangium of R. seeberi, with globular bodies[2]

Rhinosporidium spp are a saprophytic opportunistic fungus which can cause nasal rhinosporidiosis in humans, horses, cattle and dogs[3].

Rhinosporidiosis is a chronic granulomatous mycotic disease of the mucocutaneous tissues caused by Rhinosporidium seeberi.

This fungus, which is normally present in decaying vegetable matter, stagnant water or dust presumably serves as the source of infection, and local trauma to the nasal mucosa seems to predispose to disease[4].

Rhinosporidiosis occurs in tropical regions worldwide but has been reported primarily in the Americas, India[5] and south-east Asia, but has been reported in England[6].

Rhinosporidium normally resides within crypts of turbinate epithelium and are slow growing, causing localized proliferation of granulation tissue[7]. This granulomatous response results in polyps, tumors or papillomas primarily affecting the mucous membranes of the nostrils or ocular conjunctivae. These growths are friable, highly vascularized and hyperplastic and tend to bleed following severe sneezing or facial rubbing.

Multiple host-specific strains have been identified, implying cross-species transmission between humans, cattle, dogs and other mammals[8].

Clinically affected dogs usually present with chronic episodic sneezing and nasal discharge. Severe cases may result in epistaxis and blood nasal discharge.

On rhinoscopy, granulomatous masses may be visible on the nasal turbinates. Impression smears and histopathology usually reveal lymphoplasmacytic and neutrophilic inflammation with spores typical of Rhinosporidium[9].

Diagnosis is based on cytological evidence of 5- to 10-μm endospores and 50- to 1,000 μm sporangia, with definitive diagnosis confirmed by dotELISA or PCR assaying[5].

A differential diagnosis would include other causes of mycotic rhinitis such as Cryptococcus spp, Aspergillus fumigatus or Penicillium spp[10].

Treatment usually requires surgical curettage under general anesthesia, followed by parenteral antifungal therapy such as itraconazole, ketaconazole or terbinafine.

In non-responsive cases, a rhinotomy may be performed and a topical clotrimazole[11] or povidone-iodine dressing is placed as a 'tie-over' dressing, replaced every 2 - 3 days until all exposed tissue is covered by healthy granulation tissue[12].

Dapsone has also been used to treat nasal rhinosporidiosis[13].

References

  1. Easley JR et al (1986) Nasal rhinosporidiosis in the dog. Vet Pathol 23(1):50-56
  2. Hoff B & Hall DA (1986) Rhinosporidiosis in a dog. Can Vet J 27(6):231-232
  3. Fredricks DN et al (2000) Rhinosporidium seeberi: a human pathogen from a novel group of aquatic protistan parasites. Emerg Infect Dis 6(3):273-282
  4. Jungerman, PF & Swartzmann, RM (1972) Rhinosporidiosis. In: Veterinary medical mycology. Philadelphia: Lea & Febiger. pp:40-47
  5. 5.0 5.1 Sudasinghe T et al (2011) The regional sero-epidemiology of rhinosporidiosis in Sri Lankan humans and animals. Acta Trop 120(1-2):72-81
  6. Miller RI & Baylis R (2009) Rhinosporidiosis in a dog native to the UK. Vet Rec 164(7):210
  7. Meier WA et al (2006) Cytologic identification of immature endospores in a dog with rhinosporidiosis. Vet Clin Pathol 35(3):348-352
  8. Silva V et al (2005) Molecular evidence for multiple host-specific strains in the genus Rhinosporidium. J Clin Microbiol 43(4):1865-1868
  9. Hill SA et al (2010) Nasal rhinosporidiosis in two dogs native to the upper Mississippi river valley region. J Am Anim Hosp Assoc 46(2):127-131
  10. Wolf AM (1992) Fungal diseases of the nasal cavity of the dog and cat. Vet Clin North Am Small Anim Pract 22(5):1119-1132
  11. Sharman M et al (2012) Clotrimazole and enilconazole distribution within the frontal sinuses and nasal cavity of nine dogs with sinonasal aspergillosis. J Small Anim Pract 53(3):161-167
  12. Moore AH (2003) Use of topical povidone-iodine dressings in the management of mycotic rhinitis in three dogs. J Small Anim Pract 44(7):326-329
  13. Allison N et al (1986) Nasal rhinosporidiosis in two dogs. J Am Vet Med Assoc 188(8):869-871