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.
Michael P. Jones, DVM, Dipl. ABVP
Infections 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.
Photo 1: Aspergillus sp hyphae from a nasal flush in an Amazon parrot. 100x.
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 neighboring 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.