Aspergillosis is a noncontagious, opportunistic fungal (mycotic) infection caused by Aspergillus
spores. The disease is common in chickens and other captive birds. Birds are particularly susceptible due to their unique respiratory system. A. fumigatus
is the most common causative species, followed by A. flavus
spores are ubiquitous in the environment, and grow anywhere there is organic matter and moisture, especially in warm, humid weather.
Aspergillosis can present in acute or chronic form.
- Acute form: The acute form, often referred to as brooder pneumonia, is usually seen in young chicks, resulting from exposure to an overwhelmingly high concentration of fungal spores.
- Chronic form: The chronic form is typically seen in adult chickens with compromised immune systems.
Besides the two forms of aspergillosis, there are also several manifestations of the disease, depending on which body systems or organs are infected. Pulmonary aspergillosis is the form most common in chickens, manifesting as respiratory disease. Other less common forms involve infections of the eye (ophthalmitis), brain (encephalitis), skin (dermatitis), joints (osteomycosis), and viscera (systemic).
Chickens become infected with Aspergillus
spores through exposure in their environment. Any disturbances which generate large amounts of dust particles, usually contain Aspergillus
If a chicken inhales significant quantities, it can cause disease. However, the inhaled spores may not cause disease right away, and instead remain dormant in the bird's air sacs and lungs, until a stressful event or illness triggers Aspergillus
to begin to cause damage.
Early diagnosis and treatment of Aspergillosis can be difficult since obvious clinical signs often do not develop until the disease is advanced. Diagnostic testing includes blood work (complete blood count (CBC), biochemistry), fungal culture, serology, radiographs, endoscopy, and histopathology.
- Blood work: The following characteristics may be indicative of aspergillosis:
Repeated blood work can be used to evaluate disease progression and treatment success.
- Elevated liver values (aspartate aminotransferase and lactate dehydrogenase)
- Elevated creatine kinase
- Increased uric acid
- Electrolyte abnormalities
- Decreased albumin: globulin ratio (<0.5)
- Moderate to severe leukocytosis with heterophilia (25,000–100,000 cells/mcL)
- Hyperglobulinemia (beta and gamma)
- Radiographs: May be helpful for finding general cloudiness to air sac or lung fields, and pulmonary or air sac granulomas. Although, these lesions will only be seen during the later stages of the infection.
- Cytology and fungal culture: Using samples taken from the trachea, air sacs, or throat. Can be useful for detecting fungal spores. Cytology may show septate, 5- to 10-mcm-thick hyphae with straight parallel sides, ball-shaped terminal ends, and 45° branching.
- Necropsy exam: Lesions typically involve the respiratory system; chronic lesions usually involve the entire respiratory system, but acute cases can have lesions in the lungs and air sacs. Chickens with aspergillosis typically have white or yellow plaques or nodules/granulomas and a mold-like lesion, or a general cloudiness, in the air sacs and lungs of affected birds.
Aspergillosis treatment is difficult and lengthy. Therapy generally consists of 4 to 6 months of systemic antifungal agents, such as itraconazole, topical application of antifungal agents to granulomas using endoscopy, or nebulization with antifungal agents. It also requires modification of the bird's environment, and supportive care.