Equis ISSN 2398-2977


Contributor(s): Christopher Brown, Paddy Dixon, Nicola Menzies-Gow


  • Cause: infection with Aspergillus spp.
  • Sinonasal (more common), guttural pouch or pulmonary (rare: related to immunosuppression?).
  • Sinonasal form either invasive (protracted treatment) or non-invasive (often unnoticed).
  • Signs: malodorous purulent/mucopurulent unilateral nasal discharge; signs consistent with lower respiratory tract disease; epistaxis, nasal discharge and various neurologic signs.
  • Diagnosis: radiology, ultrasonography, mycology, endoscopy.
  • Treatment: surgery, topical or systemic fungicidal treatment.
  • Prognosis: sinonasal form may require treatment for months; pulmonary form has hopeless prognosis; guttural pouch form has a guarded prognosis and life-threatening hemorrhage is common.



  • Aspergillus spp Aspergillus spp.
  • Aspergillus spp are common in the equine environment, especially in moldy feed and bedding.
  • Aspergillus spp are opportunistic pathogens and often cause disease in horses that are immunosuppressed from debilitating disease or that have been treated with immunosuppressive drugs.

Predisposing factors


  • Pulmonary form: immunosuppression, eg
    • Treatment of a pre-existing condition with either antibiotics or corticosteroids.
    • Concurrent presence of debilitating disease, eg neoplasia or pituitary pars intermedia dysfunction (PPID).


  • Exposure to massive numbers of spores from moldy feeds and bedding.
  • Sino-nasal form: secondary to nasal trauma or to intra nasal/sinus surgery, eg excision of ethmoid hematoma Ethmoid: hematoma, sinus cysts Paranasal sinus: cyst.
  • Pulmonary form: opportunistic infection by fungi associated with translocation of organisms across an inflamed gastrointestinal tract, ie enterocolitis, eg following infection with Salmonella Intestine: salmonellosis or inhalation of an overwhelming number of spores resulting in fungal proliferation and invasion of the small airways.
  • Guttural pouch form: an underlying lesion of the arterial wall such as an aneurysmal dilatation has been suggested as a predisposing factor.


Sinonasal form
  • Etiology of fungal rhinitis is not known.
  • Predisposing factors could be immunosuppression or disruption of the mucosal layer owing to trauma, inflammation or infection which potentially could allow fungal invasion.
Pulmonary form
  • Acute Aspergillus bronchopneumonia due to fungal invasion and proliferation in small airways.
  • Angioinvasive pulmonary aspergillosis due to fungal infiltration of large blood vessels.

Either Pulmonary form: inhalation of massive number of spores.
Or Acute enterocolitis → mycotic invasion from gut → embolic mycotic pulmonary aspergillosis (often find multiple organ involvement, eg kidney and brain).

Guttural pouch form
  • Inhaled aspergillus spores → colonize wall of arterial vessel in the guttural pouch.
  • Growth of mycotic plaque and erosion of arterial wall → spontaneous hemorrhage → epistaxis or catastrophic hemorrhage → death.
  • More rarely, mycotic plaque impinges major nerve, eg vagus (sympathetic trunk), glossopharyngeal, hypoglossal, facial nerve → Horner's syndrome, pharyngeal paralysis and facial paralysis.


  • Pulmonary form may be asymptomatic with sudden death.
  • Invasive nasal form may persist, cause sequestration of nasal bones/cartilage and require treatment for several months.
  • Guttural pouch may be asymptomatic with sudden fatal hemorrhage.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Arnauld des Lions J, Guillot J, Legrand E, Bisseaud O & Jensens H E (2000) Aspergillosis involving the frontal sinus in a horse. Equine Vet J 12 (5), 248-250 VetMedResource.
  • Guillot J et al (1999) Comparative study of serological tests for the diagnosis of equine aspergillosis. Vet Rec 145 (12), 348-349 PubMed.
  • Johnson P J, Moore L A, Mrad D R, Turk J R & Wilson D A (1999) Sudden death of two horses associated with pulmonary aspergillosis. Vet Rec 145 (1), 16-20 PubMed.
  • Tremaine W H, Clarke C J & Dixon P M (1999) Histopathological findings in equine sinonasal disorders. Equine Vet J 31 (4), 296-303 PubMed.
  • Blomme E, Del Piero F, La Perle K M D & Wilkins P A (1998) Aspergillosis in horses: a review. Equine Vet Educ 10 (2), 86-93 VetMedResource.
  • McGorum B C, Dixon P M & Lawson G H M (1997) A review of 10 cases of mycotic rhinitis. Equine Vet Educ 4 (1), 8-12 WileyOnline.