Aspergillosis

Description

Apergillosis is a disease of the respiratory system caused by several Aspergillus spp.. Aspergillus fumigatus is the most frequently reported species in domestic animals but Aspergillus tereus has also been implicated. Aspergillus is a ubiquitous saprophyte and is found worldwide. Commonly affected species include birds, dogs, cats, horses and cattle but the disease has been reported in many other wild and domestic species. The pathogenesis of the disease remains largely unknown but is thought to be related to the formation of haemorrhagic lesions and enzymatic breakdown of tissue by elastase.

Clinical signs and features

Birds

In avian species the disease manifests as a diffuse infection of the air sacs. Two forms of the disease have been reported; a diffuse infection of the air sacs; a diffuse pneumonic form and a nodular form involving the lungs. In chicks and poults the disease is known as 'brooder pneumonia' and may affect many birds in a flock. Animals become infected due to inhalation of spores from contaminated feed or litter. Clinical signs include dyspnoea, diarrhoes, listlessness, pyrexia, loss of appetite and loss of condition. Seizures and torticollis may occasionally occur if infection disseminates to the brain.

Aspergillus in a swan Copyright Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath

Cattle

Aspergillosis has a number of clinical manifestations in the cow including mastitis, placentitis, ocular infections and mycotic pneumonia. Abortion in the second or third trimester of pregnancy has also been described. Cases of diarrhoea in calves have also been reported. Clinical signs include Lesions are usually up to 2mm in diameter and contain asteroid bodies with a germinated spore in the centre. Acute infection causes miliary lesions and chronic infections causes granulomatous and calcified lesions.

Horses

In the horse, Aspergillus most commonly affects the guttural pouches but infection may also lead to abortion, keratomycosis and rarely pulmonary aspergillosis. Guttural pouch mycosis is characterised by epistaxis as a result of fungal erosion of the internal carotid artery. Other clinical signs include nasal discharge and dysphagia. Mycotic plaques are usually located on the caudodorsal aspect of the medial guttural pouch.

Dogs

Aspergillosis is a common cause of nasal disease in dogs. Cases occur most commonly in young to middle aged male dogs, but animals of all age and of both sexes may be affected. Doliocephalic breeds are thought to be overrepresented. Clinical signs are those seens with any chronic nasal disease and include sneezing, unilateral or bilateral serosanguinous nasal discharge, ulceration of the nares, nasal pain and epistaxis. The disease is usually localised to the paranasal sinuses and nasal cavity but a disseminated form with granulomas and infarcts has been reported in dogs, particularly German Shephards. The disseminated form of disease often involves multiple organ systems including the spleen and kidneys. Clinical signs include lethargy, anorexia, haematuria, urinary incontinence and haematuria. The vertebrae are frequently affected and osteomyelitis and discospondlylitis are common features.

Aspergillus in vivo Copyright Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath

Diagnosis

In dogs, radiology is often peformed in the diagnostic work up of an animal with suspected Aspergillosis. Open-mouth ventro-dorsal views often reveal generalised radiolucency and lysis of the turbinate bones. Rhinoscopy may be used to directly visualise the lesions, revealing characteristic white-green fungal plaques. Fungal culture can be used to demonstrate the organism but should not be used as the sole means of diagnosis due to the possibility of false . Aspergillus grows on Sabauraud's Dextrose and Blood agar. White colonies form intitially which turn green, then dark green, flat and velvety

• Microscopically:
  • Conidiophores with large terminal vesicles (only visible in the lungs and air sacs where there is access to oxygen)
    • Vesicle shape varies depending on the species
  • Is a common contaminant so repeated tests should be done for a definitive diagnosis

• Pathology:
  • Aspergillus fumigatus causes rhinitis, respiratory tract inflammation and sinusitis
  • Sometimes appears on lesions of ethmoidal haematoma

Treatment

In dogs, the treatment of choice is topical application of the anti-fungal agent Clotrimazole. It is admnistered via indwelling catheters placed through a trephine hole in the frontal sinus.

References

• Carter, G. R., Wise, D. J. (2004) Essentials of Veterinary Bacteriology and Mycology Wiley-Blackwell

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  Aspergillus sporing heads

  ^{Copyright Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath}
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  Aspergillus mycelium stained with blue/black Quink

  ^{Copyright Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath}
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  Mycotic Abortion caused by Aspergillus

  ^{Copyright Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath}
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  Mycotic Abortion caused by Aspergillus

  ^{Copyright Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath}
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  Mycotic Abortion caused by Aspergillus

  ^{Copyright Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath}
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  Nasal Aspergillus

  ^{Copyright Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath}

Aspergillus fumigatus

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  Aspergillus hyphae in cattle lung

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

  ^{(Image sourced from Bristol Biomed Image Archive with permission)}

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