Aspergillosis is a fungal infection caused by Aspergillus
species, with A. fumigates
being the most common. The fungus is generally acquired through the respiratory tract, causing lesions in the air sacs, lungs, and even the central nervous system and eyes. Aspergillus
are opportunistic invaders, and healthy birds are usually resistant to infection unless they are exposed to a massive number in the environment or are vulnerable due to age, concurrent illness, chronic inflammatory condition or stress.
What are the symptoms of aspergillosis?
Aspergillosis primarily infects the respiratory tract, however any organ system may be affected. Aspergillosis may be acute or chronic in nature.
- Acute form: Generally occurs in young chicks and results in high morbidity and mortality. Onset is very quick and usually develops within a week. Most affected birds will die within a few days without emergency veterinary care. The most common signs include:
- Loss of appetite
- Weight loss
- Difficulty breathing
- Cyanosis (bluish/purplish comb)
- Chronic form: Usually very subtle in onset, and it may take several weeks or months to develop. It is most common in older birds, many with a history of malnutrition, stress, concurrent illness, or prolonged antibiotic/corticosteroid use. The entire course of the disease ranges from less than 1 week to over 6 weeks in duration. The most common clinical signs observed include:
- Change in behavior
- Weight loss
- Reduced appetite
- Exercise intolerance
- Increased respiratory rate
- Changes in vocalization (voice), often more apparent in roosters
- Audible respiratory sounds
- Tail bobbing
- Open-mouthed breathing
What are the risk factors?
Stress and subsequent immunosupression are thought to play a key role in onset of the disease.
- Pre-existing disease or chronic injury.
- Exposure to damp feed, droppings, and bedding
- Hot and humid weather conditions
- Stress - Stress is a strong immune suppressor. Any events which cause stress can increase a chicken's susceptibility to disease. Overcrowding is stressful. Example stress events include attempted predator attacks, fighting among flock members, exposure to very cold or hot temperatures, mishandling, etc.
- Prolonged use of antibiotics and/or corticosteroids.
- Poor ventilation - Aspergillus can accumulate in high concentrations in the air, as inhalable dust particles
How is aspergillosis diagnosed?
Early diagnosis and treatment of Aspergillosis can be difficult since obvious clinical signs often do not develop until the disease is advanced. Diagnostics include a complete blood count (CBC), biochemistry panel, aspergillosis antigen and antibody levels, protein electrophoresis, radiography and/or endoscopy, and fungal culture. A presumptive diagnosis of aspergillosis can usually be made based on the bird's history, clinical signs, physical exam and complete blood count (CBC).
- CBC - May show an increase in white blood cell count with monocytosis during later stages of the disease.
- 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.
- Fungal culture - May be taken of the trachea, air sacs, or throat.
How is Aspergillosis treated?
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.