Fungal diseases in birds:
Recognize infection early
Fungi are commonplace in the environment, and some are even considered normal inhabitants of the skin, gastrointestinal tract and other mucous membrane surfaces. In most situations, healthy birds can ward off infection if their immune systems are intact and fully operational. In other cases, however, the immune system may be compromised leading to the development of serious infections. Paramount to properly managing fungal infections in avian species is the ability to recognize infection early in the course of disease, to administer appropriate antifungal medications for the location and severity of infection, and to continually assess a patient's response to therapy. The scope of this article is to provide a brief overview of several fungal diseases in companion avian species.
AspergillosisInfections with Aspergillus sp, most commonly Aspergillus fumigatus, affect a wide variety of free-ranging and captive avian species. Although considered to be infectious, Aspergillus sp are noncontagious, ubiquitous, saprophytic organisms. A. flavus, A. niger, A. nidulans and A. terreus are also considered to be pathogenic in avian species.
All birds are susceptible to infection, especially young birds or those with compromised immune systems. Overcrowding, poor sanitation, poor ventilation, poor nutrition (e.g. hypovitaminosis A), exposure to respiratory toxins, age, concurrent infection and humid/dry dusty environments may facilitate exposure to an overwhelming number of spores and ultimately, the development of an infection.
Many wild avian species may be affected including raptors (goshawks, red-tailed hawks, and gyrfalcons), galliformes (pheasant, quail and turkeys), waterfowl (diving and shorebirds) and penguins. Among companion bird species there seems to be a higher prevalence of infection in blue-fronted Amazon parrots, African grey parrots and mynah birds.
Aspergillosis is often classified as either an acute or chronic disease. Acute diseases are often seen in birds exposed to an overwhelming number of fungal spores over a short period of time. The result is rapid with massive colonization of the lungs leading to a miliary granulomatous disease.
Chronic diseases may occur secondary to immunosuppression, concomitant disease or other stressor that limits the ability of the birds to fight off infection. Here granulomatous lesions often appear in areas of high oxygen tension and low blood flow such as the thoracic and abdominal air sacs and syrinx. It is important to note that Aspergillus sp spores may also spread hematogenously to other organs as a result of fungal colony extension into neighbouring vessels as well as direct extension into pneumatic bones, the coelomic cavity and surrounding structures. Fungal colonization and infection may also be limited to the specific point where the organisms enter the body including the oropharynx, gastro-intestinal tract, the eye, kidney, bone sinuses and the central nervous system.
Clinical signs vary depending upon the location and severity of infection and the integrity of the host's immune system; although peracute and acute death without any clinical signs can occur. Birds with acute infections usually exhibit a change or loss of voice, dyspnea, open-mouthed breathing, weakness, lethargy, depression, weight loss, anorexia and ataxia, paresis or paralysis resulting from CNS infection and death. Progression of the acute form is often very rapid.
The diagnosis of aspergillosis is, at times, extremely difficult and usually involves a thorough history, physical examination, laboratory diagnostics (CBC, biochemical panel, protein electrophoresis), radiography, endoscopic examination of the respiratory tract and coelomic cavity, cytology, serological testing, fungal culture and histopathology. Serologic tests performed at the University of Miami (antigen and antibody tests) and the University of Minnesota (ELISA for antibody) are available but must be interpreted carefully. Control and treatment of aspergillosis can be difficult as well as expensive.
Treatment often consists of antifungal therapy and supportive care. Antifungal medications that have been used in avian species include itraconazole, clotrimazole, terbinafine, enilconazole and amphotericin B. The latter of which is the only fungicidal drug available. Treatment and ultimately response to therapy may differ depending upon the severity and location of the infection. Therapy is usually long-term with patient response and serological testing used to monitor progress and response to therapy. The prognosis is usually considered poor. Most commonly, itraconazole (Sporonox)(Janssen Pharmaceutical, NV, Beerse, Belgium) is administered at a dose of 5-10 mg/kg orally once daily for most avian species. Extreme caution should be used if treating African grey parrots (Psittacus erithacus) with itraconazole. While some avian practitioners avoid the use of itraconazole in African grey parrots, others use a reduced dosage of 2.5-5.0 mg/kg given orally once daily.
These pigeons should be monitored closely for anorexia and depression, which is indicative of possible toxicity related to itraconazole administration. Amphotericin B (X-Gen Pharmaceuticals Inc., Northport, N.Y.) is also commonly used in conjunction with other drugs to treat aspergillosis infections in avian patients and is administered intravenously (1.5 mg/kg IV every 8hrs for 3-7 days), intratracheally (1 mg/kg IT diluted to 1cc volume in sterile water every 12 hrs for 5 days), by intraosseous catheter (1.5 mg/kg every 6 hrs for 5 days or applied directly to granulomatous lesion in the coelomic cavity. Terbinafine hydrochloride (Novartis Pharmaceuticals) has also been used to treat fungal infections in avian species at a dose of 10-15 mg/kg given orally every 12-24 hours. However, it is considered to have poor intrinsic activity against some common yeasts and molds, which suggests that combination with an azole (fluconazole or itraconazole) or amphotericin B may be required if monotherapy does not result in clinical cure of the patient. For fungal infections involving privileged sites such as the eye or brain fluconazole (Pfizer Inc.) may be considered the drug of choice. However, it is also important to note that hydroxyitraconazole, the active metabolite of itraconazole is also able to penetrate the CNS and may also be somewhat effective in treating fungal granulomatous lesions if present in the brain. Unfortunately, there is no vaccine currently available for the management of aspergillosis.
