Respiratory Fungal Infections - Pathology

()Map CARDIORESPIRATORY SYSTEM (Map) RESPIRATORY SYSTEM INFLAMMATION

Aspergillus fumigatus

Aspergillus hyphae in cattle lung (Image sourced from Bristol Biomed Image Archive with permission)

Nasal aspergillosis (Image sourced from Bristol Biomed Image Archive with permission)

• Aspergillus fumigatus
• Most commonly in dogs but also other species
• Causes rhinitis, often also involves the frontal sinus
• Chronic necrotising inflammation with friable exudate containing necrotic tissue and fungal hyphae
• Result in severe neutrophilic rhinitis/sinusitis
• These lesions can be aggressive causing destruction of turbinates and nasal septum
• Can occur secondary to areas of mucosal compromise eg: adjacent to a space-occupying lesion
• Can cause pulmonary aspergillosis especially in birds, but also other animals
  • Initiated by inhalation of spores,the most likely source of which is mouldy feed and bedding
  • Given the wide exposure that occurs, it is thought that immunodeficiency may contribute to colonisation with this organism
  • Gross lesions :
    • Multiple discrete grey/ white nodules which develop around fungal colonies
    • Blood vessels can become involved in the lesions -> invasion, haemorrhage or thrombosis
  • Histologically:
    • Granulomatous chronic lesions
    • Macrophages and epithelioid cells
    • Fibrous capsule
• In horses:
  • Nasal aspergillosis
  • Guttural pouch infections in horses - fungal plaques form on the adventitia of the carotid arteries can lead to catastrophic haemorrhage following erosion of carotid arteries!
  • Often present with epistaxis
  • May present with neurological dysfunction
  • Rarely extends to other resions: cranium, middle ear, atlanto-occipital joint
  • May extend to sinuses

Cryptococcus neoformans

• Cryptococcus neoformans
• Causes a granulomatous rhinitis, gelatinous exudate, granulomatous pneumonia
• Nodules or destructive masses which often result in facial swelling
• In severe cases, extension from nasal cavity to involve skin and oral mucosa can occur
• Can invade through adjacent structures, eg: through the cribiform plate into the brain! These cases therefore can present as a primary neurological disease.
• Microscopic:
  • Large number of fungi and only few macrophages, lymphocytes and giant cells

Blastomycosis

• Caused by Blastomyces dermatitidis
• Occurs mainly in the Americas, Middle East and Africa, occasionally in Europe
• Mainly in young dogs, occasionally other species
• Can involve almost any tissue after spread from lungs
• Gross lesions:
  • Granulomatous pneumonia
• Microscopic lesions:
  • Yeast fungi with thich walls in nodules with macrophages, neutrophils and giant cells

Histoplasmosis

• Caused by Histoplasma capsulatum
• Gross lesions in lungs:
  • Firm encapsulated granulomas (granulomatous pneumonia)
• Microscopic lesions:
  • Macrophages with inracytoplasmic yeasts
• Also in other tissues

Pneumocystis carinii

• Important cause of pneumonia in humans associated with immunodeficiency states
• It has been occasionally reported in young or immunosuppressed animals (e.g. Arabian foals with congenital immunodeficiency)
• Grossly:
  • Diffuse interstitial pneumonia
  • Patches of firmness or consolidation
• Histologically:
  • Alveoli are filled with pale staining acidophilic material (= trophozoite and cyst forms of the organism)
• It is thought that as P. carinii is often present as a latent infection, alveolar macrophages normally control the organism - a process which fails in immunodeficient states