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Aspergillosis

Bronchomycosis, Pneumomycosis

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:
    • Lethargy
    • Depression
    • 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
    • Ascites

    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.
    • Malnutrition
    • 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.

Clinical Signs

Voice change
Exercise intolerance
Difficulty breathing
Tail bobbing
Abnormal crackles or clicking noises
Nasal discharge
Increased thirst
Reduced appetite
Weight loss
Lethargy
Increased time spent laying down
Isolation from flock members
Green color in urates in feces

Diagnosis

  • History
  • Clinical signs
  • Physical exam
  • Complete blood count (CBC)
  • Fungal culture - taken of the throat, trachea or air sacs
  • Cytology
  • Endoscopy
  • Radiography
  • Histopathology
  • Postmortem exam - Often based on observation of white caseous nodules in th

Treatment

NameSummary
Supportive careIsolate the bird from the flock and place in a safe, comfortable, warm location (your own chicken "intensive care unit") with easy access to water and food. Limit stress. Call your veterinarian.
Systemic antifungal drugsMost commonly used drugs include itraconazole (10 mg/kg administered orally, twice a day), amphotericin B (1 mg/kg administered IT, TID + 1.5 mg/kg IV), ketoconazole (60 mg/ml), clotrimazole, miconazole, or fluconazole
NebulizationWith antifungal agents.
Modification of environment.

Support

Prevention

  • Minimizing use of antibiotics and corticosteroids
  • Ensure coops are designed with good ventilation, to ensure regular air flow, with or without an open window.
  • Do not overcrowd birds
  • Remove any leftover uneaten feed and/or decaying vegetable or fruit matter daily
  • Do not expose birds to moldy straw or hay
  • Frequently move feeders and water dispensers to different areas to prevent fertile areas for growth of mold
  • Conduct regular air quality tests
  • Clean any mold present off hard surfaces with water and detergent, and dry completely. Absorbent materials such as ceiling tiles, that are moldy, should be replaced.
  • Reduce the potential for condensation on cold surfaces by adding insulation.

Prognosis

Treatment is usually long-term, frustrating, and often unrewarding if the disease is not recognized until the later stages of the infection. Early treatment is essential for a postive outcome.

Scientific References

Good Overviews

Risk Factors

  • Substandard air quality
  • Living in poorly ventilated, dusty, and/or overcrowded environments
  • Exposure to old, damp, or moldy bedding
  • Repeated or prolonged use of antibiotics and steroids
  • Stress
  • Elevated ammonia levels
  • Shipping or relocating birds
  • Pre-existing disease
  • Using corncob or walnut shells as bedding
  • Exposure to eucalyptus leaves
  • Introduction of a new bird into the flock
  • Inappropriate, prolonged or stressful relocation
  • Excessive environmental heat or cold

Seasonality

WinterSpringSummerAutumn