Aspergillosis - The Merck Veterinary Manual

Aspergillosis

Fungal infections in pet birds are generally caused by Aspergillus fumigatus . An opportunistic organism, it is often found in the same locations and under the same conditions as many bacterial secondary invaders. Malnutrition, especially vitamin A deficiency, is a common predisposing factor. Poor hygiene and inadequate ventilation, especially in warm, humid climates, can increase the incidence of this disease.

Clinical Findings:

Pulmonary aspergillosis, gross lesions, parrot

Rhinitis caused by Aspergillus is similar in appearance to bacterial rhinitis or sinusitis. A Gram’s stain or modified Wright’s stain of lesions or debris will often demonstrate the fungal hyphae. Infraorbital sinusitis involving aspergillosis often must be surgically debrided prior to effective therapy. Extensive or chronic fungal sinusitis may lead to osseous changes and permanent malformation of the upper respiratory architecture.

Tracheitis due to aspergillosis can occur in immunocompromised birds. Aspergillus granulomas often form in the syrinx of both psittacines and raptors and are particularly challenging to treat. Changes in vocalization may occur prior to dyspnea. Often these birds will stretch out their necks in order to attempt to get more oxygen.

Lower respiratory disease, including air sacculitis, often involves invasion by Aspergillus . Granulomas of the air sacs or coelomic cavity are also common, usually in the caudal thoracic or abdominal air sacs. These lesions may require surgical resection.

Diagnosis:

Antibody titers are of use in some species for aid in diagnosis of this condition. Antigen tests may also be helpful. False negatives and false positives occur with these tests. Serum electrophoresis with elevated β-globulins is consistent with aspergillosis. An absolute monocytosis and heterophilia with a significantly increased total WBC count are usually present. Direct visualization, cytology, and fungal culture may be necessary to confirm the diagnosis. Low fungal viability may yield a negative culture despite confirmation by cytology.

Treatment:

There have been significant advances in the treatment of aspergillosis in recent years. Amphotericin B is still used in nebulization, nasal flushes, and intratracheal and IV administration and is the only completely fungicidal agent available. For nebulization, it is used at a concentration of 0.25-1 mg/mL of sterile water. The concentration for nasal and sinus flushes is generally more dilute (0.05 mg/mL of sterile water). Amphotericin should not be diluted with NaCl, because this decreases its potency.

The addition of hyaluronidase to the nasal flush may increase the penetration of the antimicrobial agent by its action on hyaluronic acid in the caseated debris in the sinus. The usual dosage for hyaluronidase is 75-150 IU/10 mL of flush. The appropriate antimicrobial may be added to this flush solution. Several flushes of unmedicated warm isotonic saline or sterile water should be employed prior to a final infusion of the medicated mixture. Organic debris obtained by these preliminary flushes can be used for cytology and culture. Care must be exercised to maintain the bird’s head in a downward position to avoid the potential for aspiration of the infected debris into the lower respiratory tract.

Itraconazole (5-10 mg/kg, PO, every 24-48 hr) is the most commonly used azole for systemic Aspergillus infections in the USA. African Gray parrots ( Psittacus erithacus ) seem particularly sensitive to regurgitation and anorexia and generally receive a lower dosage—2.5-5 mg/kg, sid. Clotrimazole (10 mg/mL) is being used more frequently for nebulization in birds. Terbinafine (10 mg/kg, PO, sid) is used with increasing frequency in conjunction with or in lieu of itraconazole.

Although treatment protocols have improved, many birds infected with aspergillosis have underlying problems. Chronic vitamin A deficiency and squamous metaplasia, immunocompromise, and the scarring and thickening of air sacs that occur following an infection all provide an environment for reinfection, which is common.

If Aspergillus granulomas have formed, surgical removal (with placement of an abdominal breathing tube) can be attempted, as can flushing or aspiration of the granuloma using endoscopic equipment. Recurrence of the granuloma, secondary inflammatory changes, and the production of hyaline membranes subsequent to infection in this area are common.