Aspergillosis is an opportunistic, noncontagious fungal infection caused by
inhalation of spores of ubiquitous, saprophytic fungi of the genus Aspergillus
. The three most common species of this genus are A. fumigatus
and A. niger
, which cause aspergillosis, and A. ﬂavus
, which produces a mycotoxin (aﬂatoxin).
The disease usually affects the respiratory tract, but infections also can occur in the skin, bone, eye, gastrointestinal tract, and central nervous system. Aspergillosis is most often seen in chickens with poor immune systems and/or exposed to moldy or dusty environments with poor ventilation.
What are the symptoms of Aspergillosis?
Clinical signs associated with aspergillosis are somewhat nonspecific, and differ depending on the form, health of the chicken, and which organs are involved.
- Acute form: This form of the disease occurs very rapidly and is believed to be caused by exposure to an overwhelming number of Aspergillus conidia. This form is most often seen in young chicks. Most affected birds will die within a few days without emergency veterinary care. The most common symptoms include:
- Tail bobbing
- Open mouth breathing
- Sudden depression
- Loss of appetite
- Crop stasis
- Cyanosis (bluish/purplish comb)
- Chronic form: This form of the disease has a much more subtle onset, taking several weeks to 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 most common clinical symptoms observed include:
- Change or loss of voice, often more apparent in roosters by lack or change in crow sounds.
- Weight loss
- Open mouth breathing
- Cyanosis (blue/purple comb/wattles)
- Decreased appetite
- Disseminated aspergillosis: This form of the disease occurs when there are encephalitic and meningoencephalitic lesions in the brain involved. Clinical signs often consist of:
- Torticollis (wry neck)
- Repeated falling on side or back
- Difficulty moving
- Wing drooping
- Unsteady gait
- Mycotic keratitis: Occurs when infection occurs in the eye. Most common clinical signs include:
- Sticky, swollen eyelids
- Eye swelling
- Eye discharge
- Blepharospasm (eyelid spasm)
- Sensitivity to light
- Cloudy cornea
- Cheesy yellow exudates within the conjunctival sac
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.